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Sunlight may cut MS risk by itself: study complicates theories about the role of vitamin D.

Ultraviolet radiation from the sun seems to thwart multiple sclerosis, but perhaps not the way most researchers had assumed, a new study in mice suggests.

If validated in further research, the finding could add a twist to a hypothesis that has gained credence in recent decades. The report appeared online March 22 in the Proceedings of the National Academy of Sciences.

Scientists have observed that MS is rare in the tropics and more common at high latitudes, presumably because people living nearer the equator synthesize more vitamin D thanks to more sun exposure.

But a direct cause-and-effect relationship between vitamin D deficiency and MS has never been established. In recent mouse experiments, biochemist Hector DeLuca and his team at the University of Wisconsin-Madison tested the link between vitamin D and MS risk and came away unconvinced.

In MS, the immune system attacks fatty myelin sheaths that insulate nerves. DeLuca and his team induced a condition comparable to human MS in mice by injecting the animals with proteins that instigate similar myelin damage.

The researchers exposed some mice to UV light before and after giving the animals the damaging injection. Another group of mice got the injection but not the UV exposure.

The mice exposed to UV suppressed the MS-like disease better than the control mice, the researchers found, even though the UV radiation dose wasn't enough to greatly increase the animals' blood concentrations of vitamin D.

In another test, the scientists gave the mice varying doses of vitamin D supplements, but did not expose the animals to UV light. At safe doses, the supplements failed to control the disease.

"We concluded that UV light is doing something beyond" making vitamin D, DeLuca says.

Multiple sclerosis risk might well be influenced by a biological mechanism apart from vitamin D blood levels, but many questions remain, including how UV radiation might inhibit the immune system and the development of the disease, says George Ebers, a neurologist at the University of Oxford in England.

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Title Annotation:Body & Brain; multiple sclerosis
Author:Seppa, Nathan
Publication:Science News
Geographic Code:1USA
Date:Apr 24, 2010
Words:331
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