meteopathy or ‘weather sense’, is a word only recently introduced into English (from the French méteopathique, Italian meteopatico, the nearest equivalent of which, in common parlance, is the expression ‘under the weather’).

Most people who live in urban societies claim to be unaffected by the weather. But for a minority, the approach of bad weather may be accompanied by unpleasant symptoms (headaches, limb pains, nausea, etc., depending on the individual), and of vaguer feelings better described as changes of mood (lethargy, uneasiness, irritability, depression). Conversely, when meteorological conditions improve, these individuals experience a sense of well-being and the adverse symptoms disappear. Although still not entirely scientifically respectable, there is interest in the biological basis of such phenomena. Indeed, a serious academic organ, the International Journal of Biometeorology, publishes research in this field.

Of particular interest, given the medical and economic consequences, is the Föhn effect (or Föhn illness) affecting people living in Geneva and southern Germany, where the Föhn winds, in their passage over the Alps, become electrically charged. At least one regional newspaper (the Münchner Merkur) carries a ‘Bioweather’ (Biowetter) forecast alongside the daily weather map. Similar geography produces an excess of positive over negative ions in Canada's chinook winds. The symptoms of so-called ‘Pos-Ion’ sufferers range from mild headaches to suicidal tendencies. The Meteorological Office, UK, does not measure atmospheric charge.

Rather little is known of the physiology or the functions of our ‘weather sense’. The best physical predictor of meteorological change is atmospheric pressure, but sensory receptors responding to this stimulus have not been identified in the body of any animal. On the other hand, ‘weather’, as distinct from climate and season, is not so much a physical as a perceptual concept — made up of local phenomena that alter from day to day and hour to hour. The changes in temperature, humidity, air movement, and light produced by a rise or fall of the barometer can all be picked up, consciously or unconsciously, by traditional sense organs. The eye, acting as a light meter, by way of the small number of optic nerve fibres that run directly to the hypothalamus, can monitor the drop in light intensity as cloud cover builds up. The skin, with its hair follicles and many free nerve endings, might be responsible for ‘Pos-Ion’ sensitivity and for sensing the excess of negative charge associated with good weather.

Neural centres for integrating such diffuse information, and perhaps for altering sensitivity to pain and other stimuli, are likely to be in the parts of the brain responsible for sleep, wakefulness, and motivation. Like the weather states they mirror, the moods of meteopathics vary over a wide range.

The experiences of meteopathics are usually explained away in pathological terms (as disturbance of normal functioning). But that overlooks a possible biological function: a ‘predictive’ role essential for the survival of our hunter-gatherer ancestors. Great adaptive value would attach to any and all senses that altered mood and motivations in advance of a storm or to prepare for a spell of fine weather. The same would hold for other animals. Pathological consequences of our ‘weather sense’ may arise from man-made environments that inadvertently mimic certain weather conditions. This might account for so-called ‘Sick Building’ syndrome.

Conversely, the view that meteopathy is evolutionarily adaptive may be extended to some of the manifestations of the condition called Seasonal Affective Disorder (SAD). A craving for carbohydrates, weight increase, hypersomnia, mild depression, and inertia, which trouble some people, especially women, during the autumn months, have all been regarded as the body preparing itself for the ‘natural’ hardships of winter. The fact that bright light is effective in treating SAD, especially if delivered in the morning (10 000 lux for half an hour, or lower intensities for much longer, irrespective of wave length), supports the hypothesis that SAD is triggered by a decline in the amount of daylight in northern latitudes during the latter part of the year. Phototherapy, with light influencing the pineal gland, probably via the optic nerve fibres that run to the hypothalamus, alters the production of the chemical transmitters, melatonin and serotonin, which, in turn, influence bodily rhythm and mood. Perhaps the pineal gland, that ancient third eye, considered by René Descartes to be the seat of the soul, had the more prosaic but still somewhat intangible function of keeping the body in harmony with the seasons, much as neighbouring parts of the brain kept it in tune with the weather.

Andrew Packard

See also body clock; brain stem; hypothalamus; pain; pineal gland; sleep.