Sunbathing may reduce risk of MS, says study

The dangers of exposure to the sun may have to be reassessed after a study by a former government chief medical officer published today suggests that sunshine protects against multiple sclerosis, the degenerative disease that affects 85,000 people in Britain.

The dangers of exposure to the sun may have to be reassessed after a study by a former government chief medical officer published today suggests that sunshine protects against multiple sclerosis, the degenerative disease that affects 85,000 people in Britain.

The study by Sir Donald Acheson, who was a reader in medicine at Oxford and subsequently chief medical officer from 1983 to 1991, and his colleagues shows that people who spent more time in the sun were less likely to get MS than those who stayed out of it.

The researchers examined cancer rates in 430,000 patients treated in Oxford between 1963 and 1999 for a range of neurological and immune-related diseases and compared them with cancer rates in 5,000 patients with MS.

The results showed no difference in rates of cancer in general between the two groups. But when skin cancer rates were examined, they were significantly lower in the group with multiple sclerosis.

Skin cancer is caused by prolonged exposure to the sun, and melanoma, the severest form, by intermittent intense exposure. The findings suggest those who spend most time in the sun, as measured by their high skin cancer rates, have less chance of developing multiple sclerosis.

The researchers say in the Journal of Epidemiology and Community Health that it is the first direct evidence that sunshine protects against multiple sclerosis. A minimum level of exposure may be necessary throughout the year.

The theory that the sun could protect against MS is more than 40 years old. Sir Donald was one of the first epidemiologists to note that MS was less common among white populations living closer to the equator, such as Queensland in Australia, and more common in countries more distant from the equator such as New Zealand, in research published in 1960 and 1961.

The same observation was made in North America where multiple sclerosis was less common in sunny Florida than in relatively gloomy Chicago. But that difference has disappeared over recent decades as the incidence of the disease has risen in the southern United States. One theory now being investigated is that it is due to increased use of sunscreens.

Professor Michael Goldacre of Oxford University, who led the study, said it was too soon to revise public health advice about sun exposure. "Our study was aimed at trying to unravel the factors that might cause MS. It would be quite another matter to translate that into advice about how long to spend in the sun. We have not done the risk-benefit analysis."

Sir Donald said yesterday that he had been surprised to discover that differing levels of exposure to the sun within the UK affected the incidence of MS. "If this shows up even in England, where we think we don't get enough sun, then it shows that it is a very powerful factor," he said.

The causes of multiple sclerosis are not understood but it is thought to be a virus that triggers an auto-immune process which destroys the myelin sheath surrounding the nerves. The ultraviolet light naturally occurring in sunshine may inhibit the immune process.

Sir Donald said it was unclear whether sunlight exerted its effect through vitamin D (produced by the action of sun on the skin) or by a different mechanism. "We do not know what the mechanism is. We are keeping an open mind."

Women who take vitamin D supplements are 40 per cent less likely to develop MS, according to a study published in the US journal Neurology this week. But Sir Donald said that the pattern of multiple sclerosis did not mirror that of rickets, the bone disease linked with vitamin D deficiency.

Asked if official advice to stay out of the sun should be altered, Sir Donald said: "It is a question of balance."