Vitamin D

Definition

Purpose

Description

Precautions

Interactions

Complications

Parental concerns

Resources

Definition

Vitamin D is a fat-soluble steroid compound that the body needs to remain healthy. In some ways, vitamin D is not a true vitamin because the skin can make vitamin D when exposed to sunlight. However, if the body does not make enough vitamin D, additional amounts must be acquired through diet.

Purpose

The main role of vitamin D is to regulate amount of calcium circulating in the blood. Calcium is a mineral acquired through diet that is involved in building bones, muscle contraction, and nerve impulse transtransmission.

Vitamin D

(Illustration by GGS Information Services/Thomson Gale.)

mission. Vitamin D helps regulate the absorption of calcium from the small intestine. Too little vitamin D can cause weak, brittle, deformed bones. There is also evidence that vitamin D plays a role in controlling cell differentiation and may help to protect the body from developing some types of cancer.

Description

Vitamin D exists in several forms, two of which are important to humans. Vitamin D2, called ergocalciferol, is made by plants. Vitamin D2 can be manufactured synthetically by irradiating yeast. This type of vitamin D is most often found in dietary supplements and foods fortified with vitamin D. Vitamin D3, called cholecalci-ferol, is made naturally by the skin when it is exposed to ultraviolet rays in sunlight. Neither vitamin D2 nor D3 is active in the body. Both must be converted, first in the liver and then in the kidney, into an active form of vitamin D (1alpha, 25-dihydroxyvitamin D). Vitamin D in this topic means the active form of vitamin D.

Vitamin D's role in health

Although Vitamin D has been known to play a role in bone health for many years, only recently have researchers begun to explore its effects on cell differentiation and the immune system.

BONE HEALTH. The role of vitamin D and calcium are closely connected. The body needs calcium to build bones and teeth, contract muscles, transmit nerve

KEY TERMS

Cell differentiation —The process by which stem cells develop into different types of specialized cells such as skin, heart, muscle, and blood cells.

Fat-soluble vitamin —A vitamin that dissolves in and can be stored in body fat or the liver.

Hormone —A chemical messenger that is produced by one type of cell and travels through the bloodstream to change the metabolism of a different type of cell.

Mineral —An inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples: zinc, copper, iron.

Osteoporosis —A condition found in older individuals in which bones decrease in density and become fragile and more likely to break. It can be caused by lack of vitamin D and/or calcium in the diet.

Placebo —A pill or liquid given during the study of a drug or dietary supplement that contains no medication or active ingredient. Usually study participants do not know if they are receiving a pill containing the drug or an identical-appearing placebo.

Steroid —A family of compounds that share a similar chemical structure. This family includes the estrogen and testosterone, vitamin D, cholesterol, and the drugs cortisone and prendisone.

Vitamin —A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.

impulses, and help blood to clot. Vitamin D helps the body get the calcium it needs by increasing the amount of calcium absorbed in the small intestine. Vitamin D is an active part of the feedback loop that maintains a normal level of calcium in the blood.

To maintain health, the amount of calcium in the blood must stay within a very narrow range. When the amount of calcium in the blood falls below normal, the drop is sensed by the parathyroid glands. The parathyroid glands are four separate clusters of specialized cells in the neck. Low blood calcium levels stimulate the parathyroid glands to secrete parathyroid hormone (PTH). PTH travels through the bloodstream and stimulates the kidney to increase the conversion of vitamin D2 and D3 into its active form. Active vitamin D is released into blood and stimulates the cells lining the small intestine to increase the amount of calcium that they absorbed from digesting food. Vitamin D also causes the kidney to conserve calcium so that less is lost in urine. If these actions do not return the level of calcium in the blood to normal, vitamin D activates cells called osteoclasts that break down bone and return calcium from the bone to the bloodstream. People who do not have enough vitamin D absorb less calcium from the food they eat. To make up for this, calcium is taken from their bones and the bones weaken and break more easily.

CANCER PREVENTION AND TREATMENT. Vitamin D also helps regulate cell differentiation. During development, cells divide over and over again. At some point, they are triggered to specialize (differentiate) into different types of cells, for example, skin, muscle, blood, or nerve cells. Vitamin D joins with other compounds to turn on and off more than 50 different genes that stop cell growth and start cell differentiation.

One characteristic of cancer cells is that they grow wildly, dividing many times more than normal cells without differentiating. Since vitamin D can stimulate cells to stop dividing and begin differentiating, researchers are investigating whether vitamin D can protect people from getting certain cancers, especially colon, prostate, skin, and breast cancer. The research has produced mixed results. Some studies found that vitamin D protected against colon cancer, while other found it offered no protection. The official position of the American Cancer Society described in their 2006 Nutrition and Physical Activity Guidelines states,“There is a growing body of evidence from population studies (not yet tested in clinical trials) that vitamin D may have helpful effects on some types of cancer, including cancers of the colon, prostate, and breast.” However, the American Cancer Society makes no recommendations on the amount of vitamin D needed to have a beneficial effect. Clinical trials are underway to determine safety and effectiveness of vitamin D in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials at <http://www.clinicaltrials.gov>

OTHER DISORDERS. Vitamin D has been proved to successfully to treat a few other disorders. Psoriasis, a skin disorder, often responds to ointments that contain synthetic vitamin D3 when other treatment options have failed. When the parathyroid glands fail to function or are removed during surgery, vitamin D supplements help make up for the lack of PTH. Supplements are also used to treat rare inherited familial hypophosphatemia and Fanconi syndrome-related hypophosphatemia. Both of these are characterized by abnormally low levels of phosphate in the blood.

Normal vitamin D requirements

The United States Institute of Medicine (IOM ) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals . The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA ) defines the average daily amount of the nutrient needed to meet the health needs of 97-98 % of the population. The Adequate Intake (AI ) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

The IOM has not set RDA values for vitamin D because of incomplete scientific information and variability in the amount of vitamin D the body makes when the skin is exposed to sunshine. Instead, it has set AI and UL levels. Recently the UL level has become somewhat controversial and has been challenged by some researchers as being set too low. AI and UL levels are measured in both weight (micrograms or mcg) and international units (IU ). The IU measurement is the measurement used on dietary supplement labels. For vitamin D, 1.0 mcg equals 40 IU.

The following are the AIs and ULs for vitamin D for healthy individuals:

• infants 0-12 months: AI 200 IU or 5 mcg; UL 1,000 IU or 25 mcg .
• children 1-18 years: AI 200 IU or 5 mcg; UL 2,000 IU or 50 mcg .
• adults 19-50 years: AI 200 IU or 5 mcg; UL 2,000 IU or 50 mcg .
• adults 51-70 years: AI 400 IU or 10 mcg; UL 2,000 IU or 50 mcg.
• adults 71 years and older: AI 600 IU or 15 mcg; UL 2,000 IU or 50 mcg .
• pregnant and breastfeeding women: AI 200 IU or 5 mcg; UL 2,000 IU or 50 mcg

Exposing the face, arms, and legs to sunshine for 15 minutes three or four times a week meets the dietary requirements for vitamin D for people with fair skin much of the time. However, people who live north of 40° latitude (approximately a line that extends from Philadelphia to San Francisco) may not get enough sun exposure to meet their dietary needs during winter months. Dark-skinned people may need to spend triple the amount of time in the sun as fair-skinned people to synthesize adequate amounts of vitamin D, since the increased amount melanin pigment in dark skin slows vitamin D production. Using sunscreen with an SPF of 8 or higher also slows the production of vitamin D in the skin.

Vitamin D is not found in large amounts in many foods. However, since the 1930s vitamin D has been added to about 99%: of all milk, and to some breakfast cereals, bread, orange juice, and infant formula. In addition, the Food and Drug Administration requires all foods containing olestra, a compound that reduces fat absorption, to be fortified with the fat-soluble vitamins A, D, E, and K.

The following list gives the approximate vitamin D content for some common foods:

• cod liver oil, 1 Tablespoon: 1,360 IU
• salmon, cooked, 3.5 ounces: 360 IU
• mackerel, cooked, 3.5 ounces: 345 IU
• tuna, canned in oil, 3 ounces: 200 IU
• milk, any type fortified, 1 cup: 100 IU
• orange juice, fortified, 1 cup: 100 IU
• cereal, fortified, 1 serving: 40 IU (average, serving sizes vary)
• egg, 1 whole: 20 IU

Precautions

Vitamin D deficiency

Vitamin D deficiency results in rickets in children and osteomalacia in adults. Rickets is a condition in which the bones do not harder because of a lack of calcium deposited in them. Instead they remain soft and become deformed. Osteomalacia is a weakening of bones in adults that occurs when they are broken down (demineralized) and calcium in the bones is returned to the blood. Vitamin D deficiency also can cause joint and muscle pain, and muscle spasm. Less severe cases can result in osteoporosis in older adults.

The vitamin D fortification program, along with the popularity of daily multivitamins, has greatly reduced the number of people in the United States who are vitamin D deficient. However some groups remain at risk of vitamin D deficiency. These include:

• infants who are exclusively breastfed. Breast milk provides only about 25 UL of vitamin D per quart (liter). The American Academy of Pediatrics recommends vitamin D supplements beginning no later than 2 months of age for babies who are only fed breast milk.
• institutionalized or homebound people who rarely go outside. One study found that 60% of nursing home patients were vitamin D deficient.
• people living in northern latitudes who cover almost all their body for much of the year due to climate or religious requirements
• people with gastrointestinal diseases such as Crohn's disease, celiac disease, or inflammatory bowel disease that interfere with the absorption of nutrients from the intestine
• people with disorders of the pancreas that interfere with the absorption of nutrients
• people with anorexia nervosa (self-starvation)
• people who have had part of their stomach or intestine surgically removed for weight loss or other reasons

Vitamin D excess

Vitamin D excess in healthy individuals occurs only when large quantities of vitamin D are taken as a dietary supplement over several months. This can result in high calcium levels in the blood (hypercalcemia). Symptoms of vitamin D excess include nausea, vomiting, excessive thirst, weakness, and high blood pressure. Calcium deposits may develop in the kidneys, blood vessels, heart, and lungs. The kidneys may be permanently damaged and eventually fail completely.

Interactions

Research suggests that the following types of medications may increase the available amount of vitamin D in the body. People taking these drugs should not take a vitamin D supplement without consulting their healthcare provider.

• birth control pills
• hormone replacement therapy/estrogen replacement therapy
• isoniazid (INH) used to treat tuberculosis
• thiazide diuretics

Research suggests that the following types of medications may decrease the available amount of vitamin D in the body. People taking these drugs should discuss with their healthcare provider whether a vitamin D supplement is right for them.

• antacids taken daily for long periods
• calcium-channel blockers used to treat heart conditions and high blood pressure
• certain cholesterol-lowering medications that block fat absorption
• phenobarbitol and similar anticonvulsants
• mineral oil taken on a daily basis
• orlistat, a weight loss drug marketed as Xenical or Alli

Complications

No complications are expected when vitamin D is used in the recommended amounts. The complications resulting from insufficient or excess use are discussed above.

Parental concerns

Parents should be aware that the RDA and UL for vitamins and minerals are much lower for children than for adults. Accidental overdose may occur if children are give adult vitamins or dietary supplements.

Resources

BOOKS

Gaby, Alan R., ed. A-Z Guide to Drug-Herb-Vitamin Interactions Revised and Expanded 2nd Edition: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. New York: Three Rivers Press, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.

PERIODICALS

Carpenter, Kenneth J. and Ling Zhao.“Forgotten Mysteries in the Early history of Vitamun D.” Journal of Nutrition, 129 (1999):923-7.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995. Telephone: (800) 877-1600. Website: <http://www.eatright.org>

Linus Pauling Institute. Oregon State University, 571 Weniger Hall, Corvallis, OR 97331-6512. Telephone: (541) 717-5075. Fax: (541) 737-5077. Website: <http://lpi.oregonstate.edu>

Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892-7517 Telephone: (301)435-2920. Fax: (301)480-1845. Website: <http://dietary-supplements.info.nih.gov>

OTHER

American Cancer Society.“Can Vitamin D Prevent Cancer?” American Cancer Society, December 29, 2005. <http://www.cancer.org/docroot/NWS/content/NWS_1_1x_Can_Vitamin_D_Prevent_Cancer.asp>

Finberg, Laurence.“Rickets.” emedicine.com, April 25, 2006. <http://www.emedicine.com/ped/topic2014.htm>

Harvard School of Public Health.“Vitamins.” Harvard University, November 10,2006.<http://www.hsph.harvard.edu/nutritionsource/vitamins.html>

Maryland Medical Center Programs Center for Integrative Medicine.“Vitamin D.” University of Maryland Medical Center, 2002. <http://www.umm.edu/altmed/ConsSupplements/VitaminDcs.html/Vitamin>

Medline Plus.“Vitamin D.” U. S. National Library of Medicine, August 1, 2006. <http://www.nlm.nih/gov/medlineplus/druginfo/natural/patient-vitamind.html>

Natural Standard.“Vitamin D.” MayoClinic.com, August 1, 2006. >http://www.mayoclinic.com/health/vitamin-d/NS_patient-vitamind>

Office of Dietary Supplements.”Dietary Supplement Fact Sheet: Vitamin D.“National Institutes of Health, April 12, 2006. <http://ods.od.nih.gov/factsheets/vitamind.asp>

Tangpricha, Vin.“Vitamin D Deficience and Related Disorders.” emedicine.com, December 22, 2006. <http://www.emedicine.com/med/topic3729.htm>

Trubo, Richard.“Researchers Conclude the ‘sunshine vitamin' is Good Medicine.” eMedicineHealth.com, February 14, 2006. <http://www.emedicinehealth.com/script/main/art.asp?articlekey=78080>

Tish Davidson, A.M.

Vitamin D

Definition

Vitamin D is a fat-soluble steroid compound that the body needs to remain healthy. In some ways, vitamin D is not a true vitamin because the skin can make vitamin D when exposed to sunlight. However, if the body does not make enough vitamin D, additional amounts must be acquired through diet .

Purpose

The main role of vitamin D is to regulate amount of calcium circulating in the blood. Calcium is a mineral acquired through diet that is involved in building bones, muscle contraction, and nerve impulse transmission. Vitamin D helps regulate the absorption of calcium from the small intestine. Too little vitamin D can cause weak, brittle, deformed bones. There is also evidence that vitamin D plays a role in controlling cell differentiation and may help to protect the body from developing some types of cancer .

Description

Vitamin D exists in several forms, two of which are important to humans. Vitamin D2, called ergocalciferol, is made by plants. Vitamin D2 can be manufactured synthetically by irradiating yeast. This type of vitamin D is most often found in dietary supplements and foods fortified with vitamin D. Vitamin D3, called cholecalciferol, is made naturally by the skin when it is exposed to ultraviolet rays in sunlight. Neither vitamin D2 nor D3 is active in the body. Both must be converted, first in the liver and then in the kidney, into an active form of vitamin D (1 alpha, 25-dihydroxyvitamin D). Vitamin D in this topic means the active form of vitamin D.

Vitamin D's role in health

Although Vitamin D has been known to play a role in bone health for many years, only recently have researchers begun to explore its effects on cell differentiation and the immune system .

BONE HEALTH The role of vitamin D and calcium are closely connected. The body needs calcium to build bones and teeth, contract muscles, transmit nerve impulses, and help blood to clot. Vitamin D helps the body get the calcium it needs by increasing the amount of calcium absorbed in the small intestine. Vitamin D is an active part of the feedback loop that maintains a normal level of calcium in the blood.

To maintain health, the amount of calcium in the blood must stay within a very narrow range. When the amount of calcium in the blood falls below normal, the drop is sensed by the parathyroid glands. The parathyroid glands are four separate clusters of specialized cells in the neck. Low blood calcium levels stimulate the parathyroid glands to secrete parathyroid hormone (PTH). PTH travels through the bloodstream and stimulates the kidney to increase the conversion of vitamin D2 and D3 into its active form. Active vitamin D is released into blood and stimulates the cells lining the small intestine to increase the amount of calcium that they absorbed from digesting food. Vitamin D also causes the kidney to conserve calcium so that less is lost in urine. If these actions do not return the level of calcium in the blood to normal, vitamin D activates cells called osteoclasts that break down bone and return calcium from the bone to the bloodstream. People who do not have enough vitamin D absorb less calcium from the food they eat. To make up for this, calcium is taken from their bones and the bones weaken and break more easily.

CANCER PREVENTION AND TREATMENT Vitamin D also helps regulate cell differentiation. During development, cells divide over and over again. At some point, they are triggered to specialize (differentiate) into different types of cells, for example, skin, muscle, blood, or nerve cells. Vitamin D joins with other compounds to turn on and off more than 50 different genes that stop cell growth and start cell differentiation.

KEY TERMS

Cell differentiation —the process by which stem cells develop into different types of specialized cells such as skin, heart, muscle, and blood cells.

Fat-soluble vitamin —a vitamin that dissolves in and can be stored in body fat or the liver

Hormone —a chemical messenger that is produced by one type of cell and travels through the bloodstream to change the metabolism of a different type of cell

Mineral —an inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples: zinc, copper, iron.

Osteoporosis —a condition found in older individuals in which bones decrease in density and become fragile and more likely to break. It can be caused by lack of vitamin D and/or calcium in the diet.

Placebo —a pill or liquid given during the study of a drug or dietary supplement that contains no medication or active ingredient. Usually study participants do not know if they are receiving a pill containing the drug or an identical-appearing placebo.

Steroid —a family of compounds that share a similar chemical structure. This family includes the estrogen and testosterone, vitamin D, cholesterol, and the drugs cortisone and prendisone.

Vitamin —a nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet

One characteristic of cancer cells is that they grow wildly, dividing many times more than normal cells without differentiating. Since vitamin D can stimulate cells to stop dividing and begin differentiating, researchers are investigating whether vitamin D can protect people from getting certain cancers, especially colon, prostate, skin, and breast cancer . The research has produced mixed results. Some studies found that vitamin D protected against colon cancer , while other found it offered no protection. The official position of the American Cancer Society described in their 2006 Nutrition and Physical Activity Guidelines states, “There is a growing body of evidence from population studies (not yet tested in clinical trials) that vitamin D may have helpful effects on some types of cancer, including cancers of the colon, prostate, and breast.” However, the American Cancer Society makes no recommendations on the amount of vitamin D needed to have a beneficial effect. Clinical trials are underway to determine safety and effectiveness of vitamin D in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials at http://www.clinicaltrials.gov.

OTHER DISORDERS Vitamin D has been proved to successfully to treat a few other disorders. Psoriasis , a skin disorder, often responds to ointments that contain synthetic vitamin D3 when other treatment options have failed. When the parathyroid glands fail to function or are removed during surgery, vitamin D supplements help make up for the lack of PTH. Supplements are also used to treat rare inherited familial hypophosphatemia and Fanconi syndrome-related hypophosphatemia. Both of these are characterized by abnormally low levels of phosphate in the blood.

Normal vitamin D requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

The IOM has not set RDA values for vitamin D because of incomplete scientific information and variability in the amount of vitamin D the body makes when the skin is exposed to sunshine. Instead, it has set AI and UL levels. Recently the UL level has become somewhat controversial and has been challenged by some researchers as being set too low. AI and UL levels are measured in both weight (micrograms or mcg) and international units (IU). The IU measurement is the measurement used on dietary supplement labels. For vitamin D, 1.0 mcg equals 40 IU.

The following are the AIs and ULs for vitamin D for healthy individuals:

• adults 19–50 years: AI 200 IU or 5 mcg; UL 2,000 IU or 50 mcg
• adults 51–70 years: AI 400 IU or 10 mcg; UL 2,000 IU or 50 mcg
• adults 71 years and older: AI 600 IU or 15 mcg; UL 2,000 IU or 50 mcg

Exposing the face, arms, and legs to sunshine for 15 minutes three or four times a week meets the dietary requirements for vitamin D for people with fair skin much of the time. However, people who live north of 40° latitude (approximately a line that extends from Philadelphia to San Francisco) may not get enough sun exposure to meet their dietary needs during winter months. Dark-skinned people may need to spend triple the amount of time in the sun as fairskinned people to synthesize adequate amounts of vitamin D, since the increased amount melanin pigment in dark skin slows vitamin D production. Using sunscreen with an SPF of 8 or higher also slows the production of vitamin D in the skin.

Vitamin D is not found in large amounts in many foods. However, since the 1930s vitamin D has been added to about 99%: of all milk, and to some breakfast cereals, bread, orange juice, and infant formula. In addition, the Food and Drug Administration requires all foods containing olestra, a compound that reduces fat absorption, to be fortified with the fat-soluble vitamins A, D, E, and K.

The following list gives the approximate vitamin D content for some common foods:

• cod liver oil, 1 Tablespoon: 1,360 IU
• salmon, cooked, 3.5 ounces: 360 IU
• mackerel, cooked, 3.5 ounces: 345 IU
• tuna, canned in oil, 3 ounces: 200 IU
• milk, any type fortified, 1 cup: 100 IU
• orange juice, fortified, 1 cup: 100 IU
• cereal, fortified, 1 serving: 40 IU (average, serving sizes vary)
• egg, 1 whole: 20 IU

Precautions

Vitamin D deficiency

Vitamin D deficiency results in rickets in children and osteomalacia in adults. Rickets is a condition in which the bones do not harder because of a lack of calcium deposited in them. Instead they remain soft and become deformed. Osteomalacia is a weakening of bones in adults that occurs when they are broken down (demineralized) and calcium in the bones is returned to the blood. Vitamin D deficiency also can cause joint and muscle pain , and muscle spasm. Less severe cases can result in osteoporosis in older adults.

The vitamin D fortification program, along with the popularity of daily multivitamins, has greatly reduced the number of people in the United States who are vitamin D deficient. However some groups remain at risk of vitamin D deficiency. These include:

• institutionalized or homebound people who rarely go outside. One study found that 60% of nursing home patients were vitamin D deficient.
• people living in northern latitudes who cover almost all their body for much of the year due to climate or religious requirements
• people with gastrointestinal diseases such as Crohn&s disease, celiac disease, or inflammatory bowel disease that interfere with the absorption of nutrients from the intestine
• people with disorders of the pancreas that interfere with the absorption of nutrients
• people with anorexia nervosa (self-starvation)
• people who have had part of their stomach or intestine surgically removed for weight loss or other reasons

Vitamin D excess

Vitamin D excess in healthy individuals occurs only when large quantities of vitamin D are taken as a dietary supplement over several months. This can result in high calcium levels in the blood (hypercalcemia). Symptoms of vitamin D excess include nausea, vomiting, excessive thirst, weakness, and high blood pressure . Calcium deposits may develop in the kidneys, blood vessels, heart, and lungs. The kidneys may be permanently damaged and eventually fail completely.

Interactions

Research suggests that the following types of medications may increase the available amount of vitamin D in the body. People taking these drugs should not take a vitamin D supplement without consulting their healthcare provider.

• hormone replacement therapy/estrogen replacement therapy
• isoniazid (INH) used to treat tuberculosis
• thiazide diuretics

Research suggests that the following types of medications may decrease the available amount of vitamin D in the body. People taking these drugs should discuss with their healthcare provider whether a vitamin D supplement is right for them.

• antacids taken daily for long periods
• calcium-channel blockers used to treat heart conditions and high blood pressure
• certain cholesterol-lowering medications that block fat absorption
• phenobarbitol and similar anticonvulsants
• mineral oil taken on a daily basis
• orlistat, a weight loss drug marketed as Xenical or Alli

Complications

No complications are expected when vitamin D is used in the recommended amounts. The complications resulting from insufficient or excess use are discussed above.

Resources

BOOKS

Gaby, Alan R., ed. A-Z Guide to Drug-Herb-Vitamin Interactions Revised and Expanded 2nd Edition: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. New York: Three Rivers Press, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.

PERIODICALS

Carpenter, Kenneth J. and Ling Zhao. “Forgotten Mysteries in the Early history of Vitamun D.” Journal of Nutrition, 129 (1999):923-7.

Tish Davidson A.M.

Vitamin D Deficiency

Definition

Vitamin D deficiency exists when the concentration of 25-hydroxy-vitamin D (25-OH-D) in the blood serum occurs at 12 ng/ml (nanograms/milliliter), or less. The normal concentration of 25-hydroxy-vitamin D in the blood serum is 25-50 ng/ml. When vitamin D deficiency continues for many months in growing children, the disease commonly referred to as rickets will occur. A prolonged deficiency of the vitamin in adults results in osteomalacia. Both diseases involve defects in bones.

Description

Vitamin D is a fat-soluble vitamin, meaning it is able to be dissolved in fat. While some vitamin D is supplied by the diet, most of it is made in the body. To make vitamin D, cholesterol, a sterol that is widely distributed in animal tissues and occurs in the yolk of eggs, as well as in various oils and fats, is necessary. Once cholesterol is available in the body, a slight alteration in the cholesterol molecule occurs, with one change taking place in the skin. This alteration requires the energy of sunlight (or ultraviolet light). Vitamin D deficiency, as well as rickets and osteomalacia, tends to occur in persons who do not get enough sunlight and who fail to eat foods that are rich in vitamin D.

Once consumed, or made in the body, vitamin D is further altered to produce a hormone called 1,25-dihydroxy-vitamin D (1,25-diOH-D). The conversion of vitamin D to 1,25-diOH-D does not occur in the skin, but in the liver and kidney. First, vitamin D is converted to 25-OH-D in the liver; it then enters the bloodstream, where it is taken-up by the kidneys. At this point, it is converted to 1,25-diOH-D. Therefore, the manufacture of 1,25-diOH-D requires the participation of various organs of the body—the liver, kidney, and skin.

The purpose of 1,25-diOH-D in the body is to keep the concentration of calcium at a constant level in the bloodstream. The maintenance of calcium at a constant level is absolutely required for human life to exist, since dissolved calcium is required for nerves and muscles to work. One of the ways in which 1,25-diOH-D accomplishes this mission is by stimulating the absorption of dietary calcium by the intestines.

The sequence of events that can lead to vitamin D deficiency, then to bone disease, is as follows: a lack of vitamin D in the body creates an inability to manufacture 1,25-diOH-D, which results in decreased absorption of dietary calcium and increased loss of calcium in the feces. When this happens, the bones are affected. Vitamin D deficiency results in a lack of bone mineralization (calcification) in growing persons, or in an increased demineralization (decalcification) of bone in adults.

Causes and symptoms

Vitamin D deficiency can be caused by conditions that result in little exposure to sunlight. These conditions include: living in northern countries; having dark skin; being elderly or an infant, and having little chance to go outside; and covering one's face and body, such as for religious reasons. Many Arab women cover the entire body with black cloth, and wear a veil and black gloves when they go outside. These women may acquire vitamin D deficiency, even though they live in a sunny climate.

Most foods contain little or no vitamin D. As a result, sunshine is often a deciding factor in whether vitamin D deficiency occurs. Although fortified milk and fortified infant formula contain high levels of vitamin D, human breast milk is rather low in the vitamin. The term fortified means that vitamins are added to the food by the manufacturer.

To say that a food is high or low in vitamin D means how much of that food needs to be eaten in order to prevent vitamin deficiency and maintain good health. An exact meaning can be provided by comparing the Recommended Dietary Allowance of vitamin D with the amount of vitamin D supplied by a particular food per day. The Recommended Dietary Allowance, also referred to as RDA, is a recommendation based on data derived from different population groups and ages. The RDA for vitamin D for adults is 200 International Units (IU) per day, and can be supplied by eating approximately 1.5 kg of beef, 2.0 kg of corn oil, or 100 kg of cabbage. Few people, though, would want to eat a kilogram of beef in one day, and no human being is capable of eating 100 kg of cabbage in a day; therefore, these foods are poor sources of vitamin D. However, saltwater fish such as salmon, herring, and sardines are rich in vitamin D, supplied from the oils produced by these fish. The RDA can also be supplied by eating roughly 50 g of salmon or 2.0 g of cod liver oil, and since fortified milk contains 400 IU per quart, half a quart of milk provides the RDA. For comparison, human breast milk contains only 4 to 60 IU per quart.

No harm is likely to result from vitamin D deficiency that occurs for only a few days a year. If the deficiency occurs for a period of many months or years, however, rickets or osteomalacia may develop. The symptoms of rickets include bowed legs and bowed arms. The bowed appearance is due to the softening of bones, and their bending if the bones are weight-bearing. Bone growth occurs through the creation of new cartilage, a soft substance at the ends of bones. When the mineral calcium phosphate is deposited onto the cartilage, a hard structure is created. In vitamin D deficiency, though, calcium is not available to create hardened bone, and the result is soft bone. Other symptoms of rickets include particular bony bumps on the ribs called rachitic rosary (beadlike prominences at the junction of the ribs with their cartilages) and knock-knees. Seizures may also occasionally occur in a child with rickets, because of reduced levels of dissolved calcium in the bloodstream.

Although osteomalacia is rare in the United States, symptoms of this disease include reduced bone strength, an increase in bone fractures, and sometimes bone pain, muscle weakness, and a waddling walk.

Diagnosis

Vitamin D deficiency is diagnosed by measuring the level of 25-hydroxy-vitamin D in the blood serum. The normal level or concentration of this form of the vitamin ranges from 25-50 ng/ml. Deficiency occurs when this level decreases to about 12 ng/ml or less. As mentioned previously, 25-OH-D is not the active form of the vitamin. It must be converted to 1,25-diOH-D in order to cause responses in various organs of the body. However, the levels of vitamin D, or of 1,25-dihydroxy-vitamin D in the blood, do not give a reliable picture of whether a person is deficient in the vitamin. For this reason, they are not measured when testing for vitamin D deficiency.

Rickets is diagnosed by x-ray examination of leg bones. A distinct pattern of irregularities, abnormalities, and a coarse appearance can be clearly seen with rickets. Osteomalacia is also diagnosed with x-ray examination. Measurements of blood plasma 25-OH-D, blood plasma calcium, and blood plasma parathyroid hormone must also be obtained for the diagnosis of these diseases. Parathyroid hormone and 1,25-diOH-D work together in the body to regulate the levels of calcium in the blood.

Treatment

Rickets heals promptly with 4,000 IU of oral vitamin D per day administered for approximately one month. During this treatment, the doctor should monitor the levels of 25-OH-D in the plasma to make certain they are raised to a normal value. The bone abnormalities (visible by x ray) generally disappear gradually over a period of 3-9 months. Parents are instructed to take their infants outdoors for approximately 20 minutes per day with their faces exposed. Children should also be encouraged to play outside. Foods that are good sources of vitamin D include cod liver oil, egg yolks, butter, and oily fish. Some foods, including milk and breakfast cereals, are also fortified with synthetic vitamin D.

Osteomalacia is treated by eating 2,500 IU per day of vitamin D for about three months. Measurements of 25-OH-D, calcium, and parathyroid hormone should be obtained after the treatment period to make sure the therapy did, in fact, result in normal blood values.

Care must be taken in treating vitamin D deficiency, since high doses of vitamin D are toxic and can result in the permanent deposit of minerals in the heart, lungs, and kidneys. Symptoms of toxicity are nausea, vomiting, pain in joints, and lack of interest in eating food. In adults, vitamin D toxicity occurs with eating 50,000 IU or more per day. In infants, toxicity occurs with 1,000 IU per day. The continued intake of toxic doses results in death.

Rickets and osteomalacia are almost always treated with oral supplements of vitamin D, with the recommendation to acquire daily exposure to direct sunlight. An alternative to sunlight is the use of an ultraviolet (UV) lamp. When using UV lamps, the eyes must be covered to protect them against damage. Many types of sunglasses allow UV light to pass through, so only those that are opaque to UV light should be used. Attempts to acquire sunlight through glass windows fail to help the body make vitamin D. This is because UV light does not pass through window glass.

Rickets may also occur with calcium deficiency, even when a child is regularly exposed to sunshine. This type of rickets has been found in various parts of Africa. The bone deformities are similar to, or are the same as, those that occur in typical rickets; however, calcium deficiency rickets is treated by increasing the amount of calcium in the diet. No amount of vitamin D can cure the rickets of a child with a diet that is extremely low in calcium. For this reason, it is recommended that calcium be given in conjunction with vitamin D supplementation.

Prognosis

The prognoses for correcting vitamin D deficiency, rickets, and osteomalacia are excellent. Vitamin D treatment results in the return of bone mineralization to a normal rate, the correction of low plasma calcium levels, the prevention of seizures, and a recovery from bone pain. On the other hand, deformities such as bowed legs and the rachitic rosary persist throughout adult life.

Prevention

Food fortification has almost completely eliminated rickets in the United States. Vitamin D deficiency can be prevented by acquiring the RDA through drinking fortified milk and eating fortified cereals. For those who cannot drink milk, supplements of pills might be considered. In some older people, a 400 IU supplement may not be enough to result in the normal absorption of calcium; therefore, daily doses of 10,000 IU per day may be needed. For infants who are fed only breast milk (and rarely exposed to sunshine), a daily supplement of 200-300 IU is recommended.

Rickets continues to be a problem in Africans and Asian Indians who migrate to Canada or Great Britain, especially where these immigrants do not drink fortified milk. Prevention of rickets in these populations is attempted through educational programs sponsored by the government.

Resources

PERIODICALS

Kinyamu, H., et al. "Serum Vitamin D Metabolites and CalciumAbsorption in Normal Young and Elderly Free-Living Women and in Women Living in Nursing Homes." American Journal of Clinical Nutrition 65 (1997): 790-797.

KEY TERMS

25-hydroxy-vitamin D— This is the form of vitamin D that is measured in order to assess vitamin D deficiency.

Cholesterol— A fat-soluble steroid alcohol (sterol) found in animal fats and oils, and in egg yolks. The human body needs cholesterol to produce vitamin D.

Fat-soluble vitamin— A vitamin that dissolves easily in fat or oil, but not in water. The fat-soluble vitamins are vitamins D, E, A, and K.

International unit (IU)— A measurement of biological activity in which one IU is equal to one mg (milligram).

Osteomalacia— Osteomalacia is a bone disease that occurs in adults and is caused by a prolonged period of vitamin D deficiency.

Rachitic rosary— Beadlike bumps present at the junction of the ribs with their cartilages—often seen in children with rickets.

Recommended Dietary Allowance (RDA)— The amount of nutrients, including vitamins, that should be supplied by foods on a daily basis to maintain normal health. Recommendations are based on data obtained from different population groups and ages.

Rickets— Rickets is a bone disease that occurs in infants and growing children and is caused by a prolonged period of vitamin D deficiency.

Vitamin D

Description

Vitamin D, also known as calciferol, is essential for strong teeth and bones. There are two major forms of vitamin D: D₂ or ergocalciferol and D₃ or cholecarciferol. Vitamin D can be synthesized by the body in the presence of sunlight, as opposed to being required in the diet. It is the only vitamin whose biologically active formula is a hormone. It is fat-soluble, and regulates the body's absorption and use of the minerals calcium and phosphorus . Vitamin D is important not only to the maintenance of proper bone density, but to the many calcium-driven neurologic and cellular functions, as well as normal growth and development. It also assists the immune system by playing a part in the production of a type of white blood cell called the monocyte. White blood cells are infection fighters. There are many chemical forms of vitamin D, which have varying amounts of biological activity.

General use

The needed amount of vitamin D is expressed as an Adequate Intake (AI) rather than an Required Daily Amount (RDA). This is due to a difficulty in quantifying the amount of the vitamin that is produced by the body with exposure to sunlight. Instead, the AI estimates the amount needed to be eaten in order to maintain normal function. It is measured in International Units (IU) and there are 40 IU in a microgram (mcg). The AI for vitamin D in the form of cholecarciferol or ergocalciferol for everyone under 50 years of age, including pregnant and lactating women, is 200 IU. It goes up to 400 IU for people 51-70 years old, and to 600 IU for those over age 70. A slightly higher dose of vitamin D, even as little as a total of 700 IU for those over age 65, can significantly reduce age-related fractures when taken with 500 mg of calcium per day.

One of the major uses of vitamin D is to prevent and treat osteoporosis . This disease is essentially the result of depleted calcium, but calcium supplements alone will not prevent it since vitamin D is required to properly absorb and utilize calcium. Taking vitamin D without the calcium is also ineffective. Taking both together may actually increase bone density in postmenopausal women, who are most susceptible to bone loss and complications such as fractures.

Osteomalacia and rickets are also effectively prevented and treated through adequate vitamin D supplementation. Osteomalacia refers to the softening of the bones that occurs in adults that are vitamin D deficient. Rickets is the syndrome that affect deficient children, causing bowed legs, joint deformities, and poor growth and development.

Vitamin D also has a part in cancer prevention, at least for colon cancer. A deficiency increases the risk of this type of cancer, but there is no advantage to taking more than the AI level. There may also be a protective effect against breast and prostate cancer , but this is not as well established. Studies are in progress to see if it can help to treat leukemia and lymphoma. The action of at least one chemotherapeutic drug, tamoxifen, appears to be improved with small added doses of vitamin D. Tamoxifen is commonly used to treat ovarian, uterine, and breast cancers.

Many older adults are deficient in vitamin D. This can affect hearing by causing poor function of the small bones in the ear that transmit sound. If this is the cause of the hearing loss , it is possible that supplementation of vitamin D can act to reverse the situation.

Some metabolic diseases are responsive to treatment with specific doses and forms of vitamin D. These include Fanconi syndrome and familial hypophosphatemia, both of which result in low levels of phosphate. For these conditions, the vitamin is given in conjunction with a phosphate supplement to aid in absorption.

A topical form of vitamin D is available, and can be helpful in the treatment of plaque-type psoriasis. It may

KEY TERMS

Osteomalacia —Literally soft bones, a condition seen in adults deficient in vitamin D. The bones are painful and fracture easily.

Scleroderma —A condition causing thickened, hardened skin.

Tetany —Painful muscles spasms and tremors caused by very low calcium levels.

Vegan —A person who doesn't eat any animal products, including dairy and eggs.

Vitiligo —Patchy loss of skin pigmentation, resulting in lighter areas of skin.

also be beneficial for those with vitiligo or scleroderma. This cream, in the form of calcitriol, is not thought to affect internal calcium and phosphorus levels. Oral supplements of vitamin D are not effective for psoriasis. The cream is obtainable by prescription only.

Evidence does not support the use of vitamin D to treat alcoholism , acne, arthritis, cystic fibrosis , or herpes.

Preparations

Natural sources

Exposure to sunlight is the primary method of obtaining vitamin D. In clear summer weather, approximately ten minutes per day in the sun will produce adequate amounts, even when only the face is exposed. In the winter, it may require as much as two hours. Many people don't get that amount of winter exposure, but are able to utilize the vitamin that was stored during extra time in the sun over the summer. Sunscreen blocks the ability of the sun to produce vitamin D, but should be applied as soon as the minimum exposure requirement has passed, in order to reduce the risk of skin cancer. The chemical 7-dehydrocholesterol in the skin is converted to vitamin D₃ by sunlight. Further processing by first the liver , and then the kidneys , makes D₃ more biologically active. Since it is fat-soluble, extra can be stored in the liver and fatty tissues for future use. Vitamin D is naturally found in fish liver oils, butter, eggs, and fortified milk and cereals in the form of vitamin D₂. Milk products are the main dietary source for most people. Other dairy products are not a good supply of vitamin D, as they are made from unfortified milk. Plant foods are also poor sources of vitamin D.

Supplemental sources

Most oral supplements of vitamin D are in the form of ergocalciferol. It is also available in topical (calcitriol or calcipotriene), intravenous (calcitriol), or intramuscular (ergocalciferol) formulations. Products designed to be given by other than oral routes are by prescription only. As with all supplements, vitamin D should be stored in a cool, dry place, away from direct light, and out of the reach of children.

Deficiency

In adults, a mild deficiency of vitamin D may be manifested as loss of appetite and weight, difficulty sleeping, and diarrhea . A more major deficiency causes osteomalacia and muscle spasm. The bones become soft, fragile, and painful as a result of the calcium depletion. This is due to an inability to properly absorb and utilize calcium in the absence of vitamin D. In children, a severe lack of vitamin D causes rickets.

Risk factors for deficiency

The most likely cause of vitamin D deficiency is inadequate exposure to sunlight. This can occur with people who don't go outside much, those in areas of the world where pollution blocks ultraviolet (UV) light or where the weather prohibits spending much time outdoors. Glass filters out the rays necessary for vitamin formation, as does sunscreen. Those with dark skin may also absorb smaller amounts of the UV light necessary to effect conversion of the vitamin. In climates far to the north, the angle of the sun in winter may not allow adequate UV penetration of the atmosphere to create D₃ Getting enough sun in the summer, and a good dietary source, should supply enough vitamin D to last through the winter. Vegans, or anyone who doesn't consume dairy products in combination with not getting much sun is also at higher risk, as are the elderly, who have a decreased ability to synthesize vitamin D.

Babies are usually born with about a nine-month supply of the vitamin, but breast milk is a poor source. Those born prematurely are at an increased risk for deficiency of vitamin D and calcium, and may be prone to tetany. Infants past around nine months old who are not getting vitamin D fortified milk or adequate sun exposure are at risk of deficiency.

People with certain intestinal, liver and kidney diseases may not be able to convert vitamin D₃ to active forms, and may need at activated type of supplemental vitamin D.

Those taking certain medications may require supplements, including anticonvulsants, corticosteroids , or the cholesterol-lowering medications cholestyramine or colestipol. This means that people who are on medication for arthritis, asthma , allergies , autoimmune conditions, high cholesterol, epilepsy, or other seizure problems should consult with a healthcare practitioner about the advisability of taking supplemental vitamin D. As with some other vitamins , the abuse of alcohol also has a negative effect. In the case of vitamin D, the ability to absorb and store it is diminished by chronic overuse of alcohol products.

Populations with poor nutritional status may tend to be low on vitamin D, as well as other vitamins. This can be an effect of poor sun exposure, poor intake, or poor absorption. A decreased ability to absorb oral forms of vitamin D may result from cystic fibrosis or removal of portions of the digestive tract. Other groups who may need higher than average amounts of vitamin D include those who have recently had surgery, major injuries, or burns . High levels of stress and chronic wasting illnesses also tend to increase vitamin requirements.

Precautions

The body will not make too much vitamin D from overexposure to sun, but since vitamin D is stored in fat, toxicity from supplemental overdose is a possibility. Symptoms are largely those of hypercalcemia, and may include high blood pressure , headache, weakness, fatigue, heart arrhythmia, loss of appetite, nausea, vomiting, diarrhea, constipation, dizziness, irritability, seizures, kidney damage, poor growth, premature hardening of the arteries, and pain in the abdomen, muscles, and bones. If the toxicity progresses, itching and symptoms referable to renal disease may develop, such as thirst, frequent urination, proteinuria, and inability to concentrate urine. Overdoses during pregnancy may cause fetal abnormalities. Problems in the infant can include tetany, seizures, heart valve malformation, retinal damage, growth suppression, and mental retardation. Pregnant women should not exceed the AI, and all others over one year of age should not exceed a daily dose of 2000 IU. Infants should not exceed 1000 IU. These upper level doses should not be used except under the advice and supervision of a healthcare provider due to the potential for toxicity.

Individuals with hypercalcemia, sarcoidosis, or hypoparathyroidism should not use supplemental calciferol. Those with kidney disease, arteriosclerosis, or heart disease should use ergocalciferol only with extreme caution and medical guidance.

Side effects

Minor side effects may include poor appetite, constipation, dry mouth, increased thirst, metallic taste , or fatigue. Other reactions, which should prompt a call to a healthcare provider, can include headache, nausea, vomiting, diarrhea, or confusion.

Interactions

The absorption of vitamin D is improved by calcium, choline, fats , phosphorus, and vitamins A and C. Supplements should be taken with a meal to optimize absorption.

There are a number of medications that can interfere with vitamin D levels, absorption, and metabolism . Rifampin, H₂ blockers, barbiturates, heparin, isoniazid, colestipol, cholestyramine, carbamazepine, phenytoin, fosphenytoin, and phenobarbital reduce serum levels of vitamin D and increase metabolism of it. Anyone who is on medication for epilepsy or another seizure disorder should check with a healthcare provider to see whether it is advisable to take supplements of vitamin D. Overuse of mineral oil, Olestra, and stimulant laxatives may also deplete vitamin D. Osteoporosis and hypocalcemia can result from long-term use of corticosteroids. It may be necessary to take supplements of calcium and vitamin D together with this medication. The use of thiazide diuretics in conjunction with vitamin D can cause hypercalcemia in individuals with hypoparathyroidism. Concomitant use of digoxin or other cardiac glycosides with vitamin D supplements may lead to hypercalcemia and heart irregularities. The same caution should be used with herbs containing cardiac glycosides, including black hellebore, Canadian hemp, digitalis, hedge mustard, figwort, lily of the valley, motherwort, oleander, pheasant's eye, pleurisy, squill, and strophanthus.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. CA: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. PA: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. AZ: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. CA: Therapeutic Research Faculty, 1999.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: Alpha Books, 1997.

Judith Turner

Vitamin D

Description

Vitamin D, also known as calciferol, is essential for strong teeth and bones. There are two major forms of vitamin D: D₂ or ergocalciferol and D₃ or cholecarciferol. Vitamin D can be synthesized by the body in the presence of sunlight, as opposed to being required in the diet. It is the only vitamin whose biologically active formula is a hormone. It is fat-soluble, and regulates the body's absorption and use of the minerals calcium and phosphorus. Vitamin D is important not only to the maintenance of proper bone density, but to the many calcium-driven neurologic and cellular functions, as well as normal growth and development. It also assists the immune system by playing a part in the production of a type of white blood cell called the monocyte. White blood cells are infection fighters. There are many chemical forms of vitamin D, which have varying amounts of biological activity.

General use

The needed amount of vitamin D is expressed as an Adequate Intake (AI) rather than a Required Daily Amount (RDA). This is due to a difficulty in quantifying the amount of the vitamin that is produced by the body with exposure to sunlight. Instead, the AI estimates the amount needed to be eaten in order to maintain normal function. It is measured in International Units (IU) and there are 40 IU in a microgram (mcg). The AI for vitamin D in the form of cholecarciferol or ergocalciferol for everyone under 50 years of age, including pregnant and lactating women, is 200 IU. It goes up to 400 IU for people 51-70 years old, and to 600 IU for those over age 70. A slightly higher dose of vitamin D, even as little as a total of 700 IU for those over age 65, can significantly reduce age-related fractures when taken with 500 mg of calcium per day.

One of the major uses of vitamin D is to prevent and treat osteoporosis. This disease is essentially the result of depleted calcium, but calcium supplements alone will not prevent it since vitamin D is required to properly absorb and utilize calcium. Taking vitamin D without the calcium is also ineffective. Taking both together may actually increase bone density in post-menopausal women, who are most susceptible to bone loss and complications such as fractures.

Osteomalacia and rickets are also effectively prevented and treated through adequate vitamin D supplementation. Osteomalacia refers to the softening of the bones that occurs in adults that are vitamin D deficient. Rickets is the syndrome that affect deficient children, causing bowed legs, joint deformities, and poor growth and development.

Vitamin D also has a part in cancer prevention, at least for colon cancer. A deficiency increases the risk of this type of cancer, but there is no advantage to taking more than the AI level. There may also be a protective effect against breast and prostate cancer, but this is not as well established. Studies are in progress to see if it can help to treat leukemia and lymphoma. The action of at least one chemotherapeutic drug, tamoxifen, appears to be improved with small added doses of vitamin D. Tamoxifen is commonly used to treat ovarian, uterine, and breast cancers.

Many older adults are deficient in vitamin D. This can affect hearing by causing poor function of the small bones in the ear that transmit sound. If this is the cause of the hearing loss, it is possible that supplementation of vitamin D can act to reverse the situation.

Some metabolic diseases are responsive to treatment with specific doses and forms of vitamin D. These include Fanconi syndrome and familial hypophosphatemia, both of which result in low levels of phosphate. For these conditions, the vitamin is given in conjunction with a phosphate supplement to aid in absorption.

A topical form of vitamin D is available, and can be helpful in the treatment of plaque-type psoriasis. It may also be beneficial for those with vitiligo or scleroderma. This cream, in the form of calcitriol, is not thought to affect internal calcium and phosphorus levels. Oral supplements of vitamin D are not effective for psoriasis. The cream is obtainable by prescription only.

Evidence does not support the use of vitamin D to treat alcoholism, acne, arthritis, cystic fibrosis, or herpes.

Preparations

Natural sources

Exposure to sunlight is the primary method of obtaining vitamin D. In clear summer weather, approximately ten minutes per day in the sun will produce adequate amounts, even when only the face is exposed. In the winter, it may require as much as two hours. Many people do not get that amount of winter exposure, but are able to utilize the vitamin that was stored during extra time in the sun over the summer. Sunscreen blocks the ability of the sun to produce vitamin D, but should be applied as soon as the minimum exposure requirement has passed, in order to reduce the risk of skin cancer. The chemical 7-dehydrocholesterol in the skin is converted to vitamin D₃ by sunlight. Further processing by first the liver, and then the kidneys, makes D₃ more biologically active. Since it is fat-soluble, extra can be stored in the liver and fatty tissues for future use. Vitamin D is naturally found in fish liver oils, butter, eggs, and fortified milk and cereals in the form of vitamin D₂. Milk products are the main dietary source for most people. Other dairy products are not a good supply of vitamin D, as they are made from unfortified milk. Plant foods are also poor sources of vitamin D.

Supplemental sources

Most oral supplements of vitamin D are in the form of ergocalciferol. It is also available in topical(calcitriol or calcipotriene), intravenous (calcitriol), or intramuscular (ergocalciferol) formulations. Products designed to be given by other than oral routes are by prescription only. As with all supplements, vitamin D should be stored in a cool, dry place, away from direct light, and out of the reach of children.

Deficiency

In adults, a mild deficiency of vitamin D may be manifested as loss of appetite and weight, difficulty sleeping, and diarrhea. A more major deficiency causes osteomalacia and muscle spasm. The bones become soft, fragile, and painful as a result of the calcium depletion. This is due to an inability to properly absorb and utilize calcium in the absence of vitamin D. In children, a severe lack of vitamin D causes rickets.

Risk factors for deficiency

The most likely cause of vitamin D deficiency is inadequate exposure to sunlight. This can occur with people who do not go outside much, those in areas of the world where pollution blocks ultraviolet (UV) light or where the weather prohibits spending much time outdoors. Glass filters out the rays necessary for vitamin formation, as does sunscreen. Those with dark skin may also absorb smaller amounts of the UV light necessary to effect conversion of the vitamin. In climates far to the north, the angle of the sun in winter may not allow adequate UV penetration of the atmosphere to create D₃. Getting enough sun in the summer, and a good dietary source, should supply enough vitamin D to last through the winter. Vegans, or anyone who does not consume dairy products in combination with not getting much sun is also at higher risk, as are the elderly, who have a decreased ability to synthesize vitamin D.

Babies are usually born with about a nine-month supply of the vitamin, but breast milk is a poor source. Those born prematurely are at an increased risk for deficiency of vitamin D and calcium, and may be prone to tetany. Infants past around nine months old who are not getting vitamin D fortified milk or adequate sun exposure are at risk of deficiency.

People with certain intestinal, liver and kidney diseases may not be able to convert vitamin D₃ to active forms, and may need at activated type of supplemental vitamin D.

Those taking certain medications may require supplements, including anticonvulsants, corticosteroids, or the cholesterol-lowering medications cholestyramine or colestipol. This means that people who are on medication for arthritis, asthma, allergies, autoimmune conditions, high cholesterol, epilepsy, or other seizure problems should consult with a healthcare practitioner about the advisability of taking supplemental vitamin D. As with some other vitamins, the abuse of alcohol also has a negative effect. In the case of vitamin D, the ability to absorb and store it is diminished by chronic overuse of alcohol products.

Populations with poor nutritional status may tend to be low on vitamin D, as well as other vitamins. This can be an effect of poor sun exposure, poor intake, or poor absorption. A decreased ability to absorb oral forms of vitamin D may result from cystic fibrosis or removal of portions of the digestive tract. Other groups who may need higher than average amounts of vitamin D include those who have recently had surgery, major injuries, or burns. High levels of stress and chronic wasting illnesses also tend to increase vitamin requirements.

Precautions

The body will not make too much vitamin D from overexposure to sun, but since vitamin D is stored in fat, toxicity from supplemental overdose is a possibility. Symptoms are largely those of hypercalcemia, and may include high blood pressure, headache, weakness, fatigue, heart arrhythmia, loss of appetite, nausea, vomiting, diarrhea, constipation, dizziness, irritability, seizures, kidney damage, poor growth, premature hardening of the arteries, and pain in the abdomen, muscles, and bones. If the toxicity progresses, itching and symptoms referable to renal disease may develop, such as thirst, frequent urination, proteinuria, and inability to concentrate urine. Overdoses during pregnancy may cause fetal abnormalities. Problems in the infant can include tetany, seizures, heart valve malformation, retinal damage, growth suppression, and mental retardation. Pregnant women should not exceed the AI, and all others over one year of age should not exceed a daily dose of 2,000 IU. Infants should not exceed 1,000 IU. These upper level doses should not be used except under the advice and supervision of a healthcare provider due to the potential for toxicity.

Individuals with hypercalcemia, sarcoidosis, or hypoparathyroidism should not use supplemental calciferol. Those with kidney disease, arteriosclerosis, or heart disease should use ergocalciferol only with extreme caution and medical guidance.

Side effects

Minor side effects may include poor appetite, constipation, dry mouth, increased thirst, metallic taste, or fatigue. Other reactions, which should prompt a call to a healthcare provider, can include headache, nausea, vomiting, diarrhea, or confusion.

Interactions

The absorption of vitamin D is improved by calcium, choline, fats, phosphorus, and vitamins A and C. Supplements should be taken with a meal to optimize absorption.

There are a number of medications that can interfere with vitamin D levels, absorption, and metabolism. Rifampin, H₂ blockers, barbiturates, heparin, isoniazid, colestipol, cholestyramine, carbamazepine, phenytoin, fosphenytoin, and phenobarbital reduce serum levels of vitamin D and increase metabolism of it. Anyone who is on medication for epilepsy or another seizure disorder should check with a healthcare provider to see whether it is advisable to take supplements of vitamin D. Overuse of mineral oil, Olestra, and stimulant laxatives may also deplete vitamin D. Osteoporosis and ypocalcemia can result from long-term use of corticosteroids. It may be necessary to take supplements of calcium and vitamin D together with this medication. The use of thiazide diuretics in conjunction with vitamin D can cause hypercalcemia in individuals with hypoparathyroidism. Concomitant use of digoxin or other cardiac glycosides with vitamin D supplements may lead to hypercalcemia and heart irregularities. The same caution should be used with herbs containing cardiac glycosides, including black hellebore, Canadian hemp, digitalis, hedge mustard, figwort, lily of the valley, motherwort, oleander, pheasant's eye, pleurisy, squill, and strophanthus.

KEY TERMS

Osteomalacia— Literally soft bones, a condition seen in adults deficient in vitamin D. The bones are painful and fracture easily.

Scleroderma— A condition causing thickened, hardened skin.

Tetany— Painful muscle spasms and tremors caused by very low calcium levels.

Vegan— A person who does not eat any animal products, including dairy and eggs.

Vitiligo— Patchy loss of skin pigmentation, resulting in lighter areas of skin.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. Therapeutic Research Faculty, 1999.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. Alpha Books, 1997.