ISSUE 2051 Friday
5 January 2001
By Charles Clover, Environment Editor
SUNLIGHT protects the body against multiple sclerosis, according to a study of the disease in different nationalities from the poles to the equator. It has been known for at least 50 years that people in high latitudes faced a 100 times greater risk of contracting the disease than people living on the equator, where the occurrence is nil.
There is even a four-fold variation in the number of cases in America between the southern states and the state of Washington, the Royal Geographical Society/Institute of British Geographers' conference in Plymouth was told.
Prof Graham Bentham, from the environmental sciences department of East Anglia University, has conducted a statistical study that he believes has explained these geographical variations for the first time. He said his study, which has yet to be published, successfully tested the hypothesis that the variation could be explained by geographical differences in exposure to ultraviolet-B (UVB) radiation, the body's principal source of vitamin D.
The study found that the higher proportion of oily fish, rich in vitamin D, in the diet of Norwegians and Icelanders was likely to account for their lower rates of contracting MS compared with other North Europeans. Until now, he said, people had been looking at several other explanations for the steep geographical differences in the prevalence of multiple scelerosis.
One was that people of high latitudes shared a genetic predisposition to MS. Another was that MS was a virus - yet to be identified - to which northern peoples had more exposures because of the longer winters. A further explanation was that MS was a response to common viruses.
Prof Bentham also found that populations which tended to eat a lot of animal fat were more likely to get multiple scelerosis. He said a possible explanation of why sunlight helped to prevent MS - a degenerative disease in which the immune system attacks the myelin protein of the central nervous system - was that it had been shown to be an immune suppressant. So sunlight was likely to suppress the body's own over-active response to itself.
He said his data was not able to distinguish between the vitamin D theory and this explanation for why sunlight worked in preventing or slowing down the disease. If it was vitamin D, this could be taken as a diet supplement or in the form of oily fish without the danger of contracting skin cancer as a result of over-exposure to sunlight.
The Multiple Sclerosis Society was wary yesterday of placing too much credence in Prof Bentham's work until it had been peer reviewed and published. Dr Lorna Layward, head of research at the society, said: "Geographical variations of incidence of MS have been known about for a long time.
"The further you go from the equator, the more likely you are to get multiple sclerosis. The problem with epidemiological studies like these is that they can make connections which may not be causal. People are looking at this and more work is needed to determine whether a causal relationship exists."
Andy Jones, a lecturer
in environmental sciences at the University of East Anglia, presented a
paper that showed that UVB radiation could help to correct high blood pressure.Vitamin
D produced by UVB radiation helped to counteract the effect of insufficient
calcium in the body.