MONDAY, Feb. 7 (HealthDay News) -- Increased sun exposure and higher vitamin D levels may help to protect against the risk of developing multiple sclerosis, a new Australian study suggests.

Multiple sclerosis is an autoimmune disease whose symptoms include loss of balance, slurred speech, muscle spasms, and difficulty walking or moving the legs or arms. Focused on residents living in Australia, the study also echoed prior findings that this disease of the brain and spinal cord strikes with greater frequency among people who live in less sunny regions farther from the equator.

Study co-author Anne-Louise Ponsonby, a professor, epidemiologist and public health physician with the Murdoch Children's Research Institute at Royal Children's Hospital in Melbourne, stressed that the exact mechanism by which sun exposure and vitamin D may help protect against a "multi-factorial disease" is not yet clear.

But vitamin D is an important agent that helps modify immune system functioning, she noted, "and laboratory studies have shown higher vitamin D levels can dampen down some of the adverse immune overactivity that occurs in autoimmune diseases such as MS."

Ponsonby and her colleagues conducted their research with the support of the National Multiple Sclerosis Society of the United States of America, the National Health and Medical Research Council of Australia, the ANZ William Buckland Foundation, and Multiple Sclerosis Research Australia. Their observations are published in the Feb. 8 issue of the journal Neurology.

Exposure to the sun results in increased vitamin D levels, since the body makes vitamin D when it is exposed to the ultraviolet B rays in sunlight.

Although past research (some conducted by the same research team) has uncovered a similar association between sun exposure and MS risk protection, the authors noted that the current finding is the first to examine the impact of sun exposure among individuals who are just experiencing precursor signs of MS, but have not yet actually been diagnosed as having the disease.

This approach, the investigators noted, ensured that the new analysis is focused solely on pre-disease sun exposure patterns, rather than sun exposure routines that might be altered after a diagnosis. (Sunlight exposure has not been shown to benefit MS patients after diagnosis.)

Between 2003 and 2006, the research team looked at 216 patients between the ages of 18 and 59 who had early pre-diagnosis signs of MS. The patients were located in one of four different locations in Australia, with latitudes ranging from 27 degrees South to 43 degrees South.

Almost 400 other study participants without any disease indications were also included in the study for comparative purposes.

All were asked to report how much time they had spent in the sun over weekends and holidays during both summer and wintertime over the course of four different time-frames: between the ages of 6 and 10; 11 and 15; 16 and 20; and during the three years leading up to the study. In addition, skin exams were conducted, and blood samples taken to measure vitamin D levels.

The result: the higher the amount of both past and recent sun exposure (as well as specifically leisure-time exposure), the lower the risk for developing early signs of MS.

Specifically noting that sun exposure ranged from 500 to 6000 kiloujules per meter squared, the authors found that for every additional 1000 kilojoules of exposure, the risk of developing the first signs of MS dropped by 30 percent.

In addition, having a higher vitamin D level was also independently linked to a lower risk for developing MS.

What's more, those living in the study regions furthest away from the equator faced a 32 percent greater risk for signs of MS than study participants who lived closest to the equator.

And lastly, those with the most signs of skin damage faced a 60 percent lower risk for developing initial indications of MS compared with those with the least amount of skin damage caused by the sun.

While advising that sun exposure "should not be discouraged," Ponsonby strongly cautioned against the sort of "excessive exposure" that can give rise to a number of adverse health consequences, including possible skin cancer.

Dr. Moses Rodriguez, a professor of neurology and immunology at the Mayo Clinic in Rochester, Minn., agrees that "it's all about not overdoing it".

"Dermatologists can get up in arms with these sorts of studies because they're saying that the amount of sun exposure that you would need to get protection against something like MS would be the amount that would increase your risk for melanoma and skin cancer dramatically," Rodriguez said.

"But in truth, it appears that your mother's idea to go out and play in the sun was not necessarily a bad idea," Rodriguez added. "It's just that everything has to be tempered. You don't, for example, want someone to go take 10,000 units of vitamin D. Yes, you need some sun exposure, and you need some vitamin D. Both appear to have some protective effect in terms of MS. But neither is the whole answer, and neither is going to cure MS."

Nicholas G. LaRocca, vice president of health care delivery and policy research at the National Multiple Sclerosis Society in New York City, praised the study for advancing scientific knowledge about MS.

"I do think this is a very important study," he said. "It really moves this field forward in terms of refining our understanding of what puts people at risk for developing MS, and what might reduce this risk."

But like Rodriguez, he also cautioned against "over-interpreting the implications of the current findings."

"Reading this [study], one might be tempted to say 'well, I should move to a sunnier climate' or 'I should dose myself with tons and tons of vitamin D,'" LaRocca said. "But I don't think we know enough to really understand what the full and most appropriate implications are. There are many contributions to MS risk, so we will need a lot more research before it becomes clear what's really going on."

More information

For more on MS, visit the U.S. National Institute of Neurological Disorders and Stroke.