Multiple sclerosis: sunlight, diet, immunology and aetiology.

Multiple sclerosis is more common in temperate latitudes, and migration studies indicate the involvement of an aetiological environmental factor in pre-pubertal life; the precise nature of this factor has never been identified and may perhaps have been overlooked. Here we suggest a simple explanation for the latitude gradient of multiple sclerosis, i.e. that it can be explained by the immunosuppressant effects of sunlight mediated via suppression of the secretion of the immunostimulatory neurohormone melatonin from the pineal gland. The effects of dietary fatty acids in multiple sclerosis also indicate the involvement of anti-inflammatory eicosanoids in its pathogenesis. We further suggest that the exceptions to the latitude gradient (e.g. Japan), which have previously been attributed to genetic factors, may in fact have a dietary basis. Since sunlight also influences the metabolism of fatty acids in the retina, it may also influence the development of retrobulbar optic neuritis-a common antecedent of multiple sclerosis. We suggest a re-examination of the epidemiology of multiple sclerosis based on an understanding of the immunological consequences of illumination of the retina by sunlight.