NEW YORK (Reuters Health) – People who have spent more time in the sun and those with higher vitamin D levels may be less likely to develop multiple sclerosis (MS), according to a new study from Australia.

The results are consistent with previous reports showing that people living close to the equator are less likely to get MS, a chronic disease that affects the central nervous system, than those at higher latitudes. Greater sun exposure, leading to higher vitamin D levels, might explain that difference in risk.

"We've known for decades that the farther away from the equator you live and grew up, the higher the risk of MS," Dr. Thomas Mack, who studies MS at the University of Southern California and was not involved with the research, told Reuters Health. "the question is, what is it that's responsible for that increase? Sunlight is a good bet, and of course vitamin D is a function of sunlight exposure."

In MS, the protective coating around nerve fibers starts breaking down, slowing the speed of signals traveling between the brain and body. Symptoms include problems with balance and muscle coordination and sometimes memory loss and trouble with logical thinking. There is no effective treatment for the condition.

About 350,000 people in the United States suffer from MS, and women are twice as likely as men to get the disease. Health care costs associated with MS are more than $10 billion each year in the U.S.

Vitamin D occurs naturally in certain foods and can be taken in supplements, but it is also manufactured by the body in response to the ultraviolet (UV) radiation in sunlight hitting the skin.

In the current study, researchers led by Dr. Robyn Lucas of the Australian National University identified 216 adults who had just started having the first symptoms of MS between 2003 and 2006. Then they found a comparison group of 395 people from the same regions of Australia as the subjects, who matched them in age and gender, but had no signs or symptoms of MS. the researchers asked everyone in both groups how much time they had spent in the sun and where they had lived at different points in their lives. All participants' skin damage from sun and the levels of vitamin D in their blood were also measured.

On average, people with the first signs of MS had been exposed to a smaller total "UV dose" over the course of their lives, calculated based on how much time they had spent in the sun and how close to the equator they had lived.

People with early MS were also less than half as likely to have high levels of skin damage caused by exposure to sunlight. In addition, vitamin D levels were five to 10 percent lower in subjects with MS than in those without MS, according to the report published in the journal Neurology.

The finding that sun exposure and vitamin D levels may be linked to MS is not a new one — UV light and vitamin D are known to dampen the kind of abnormal immune system activity that is believed to contribute to MS. but the current study differs from others in an important way, researchers say.

"our study is the first to be able to look at both sun exposure and vitamin D status right at the very first symptoms that might precede development of MS," Lucas wrote in an e-mail to Reuters Health.

"People, after they are diagnosed with MS, they change their lifestyles," said Dr. Alberto Ascherio, who studies the link between vitamin D and MS at the Harvard School of Public Health and was not involved in the current study. That might include, for example, taking more vitamin D to try to prevent their symptoms from getting worse, which could skew analyses of whether the vitamin has any protective properties before disease sets in.

The current findings do not prove that being exposed to very little sunlight or having low vitamin D levels causes MS. And while the authors tried to show that both sun exposure and vitamin D levels influence risk of MS on their own, other researchers aren't so confident it's possible to separate their effects.

"they may have independent roles, but the reality is it's extremely difficult to sort them out," Ascherio explained. for example, the authors don't know the participants' blood levels of vitamin D over the course of their lives, and it's possible that measuring someone's sun exposure over the years is really just another way of measuring how much vitamin D they had at those times.

Even though more time in the sun might help protect against MS, it is also associated with a higher rate of skin cancer — so the message of the study is not that more time outside is always better. Nor do the results mean that everyone should load up on vitamin D supplements, said Mack. "Most people have enough vitamin D anyway, at least those people that live in the sunny areas of the world," he explained. "I don't think we know yet that taking vitamin D is going to prevent MS."

The main message of the study, Lucas said, is that "small amounts of sun exposure … occurring frequently, are probably optimal both for maintaining vitamin D levels and for other health effects."

SOURCE: bit.ly/Q5TNl Neurology, online February 7, 2011.