Vitamin D Levels Might Predict Risk for MS

FRIDAY, Sept. 19 (HealthDay News) -- Children with lower levels of vitamin D seem to be at a higher risk of being diagnosed with multiple sclerosis.

So say researchers who were expected to present the findings Friday at the World Congress on Treatment and Research in Multiple Sclerosis, in Montreal.

The idea fits nicely with previous research indicating that multiple sclerosis is more common the farther away you get from the equator, in other words, in areas where there is less sunlight.

Vitamin D synthesis is triggered when ultraviolet rays from the sun hit the skin. In addition, studies have also linked vitamin D with immune system function.

"In MS, the immune system is misregulated, and we do know that there's a susceptibility in the genes we inherit from our parents. We know that something triggers the disease," explained Patricia O'Looney, vice president of biomedical research at the National Multiple Sclerosis Society. "We know from epidemiological studies that there's a higher prevalence of MS the farther away you live from the equator and, more recently, we've learned that vitamin D does regulate the immune system."

"This is an interesting study of how environmental triggers and the immune system can be involved with MS, provided that one has these susceptibility genes," she added.

"Many studies have given us a good link between vitamin D status and immune function in MS," added study author Heather E. Hanwell, a doctoral candidate in nutritional sciences at the University of Toronto. "We wanted to see whether vitamin D status was lower in children who had their first demyelinating event and were subsequently diagnosed with MS."

A first demyelinating event is essentially an attack of symptoms that could indicate trouble with the central nervous system. One quarter of children who have such an attack go on to be diagnosed with MS.

The researchers measured levels of a vitamin D biomarker in children who had had a first event.

"The biomarker of vitamin D status was significantly lower in children diagnosed with MS to date," Hanwell said. "Children diagnosed with MS had lower vitamin D levels than those not diagnosed. Another way of looking at it, as vitamin D status increased, children had a lower risk of being diagnosed."

At this point, however, Hanwell believes the findings have more research than clinical implications.

"This type of work provides impetus for further research in this area, although, for a doctor, it would be important to look at vitamin D status in patients, particularly because 75 percent of our overall study group had vitamin D levels below what we considered to be optimal."

A second study also being presented at the World Congress found that the incidence of first demyelinating events increased by 9.2 percent for each higher degree of latitude up the eastern coast of Australia. The study was partially funded by the National Multiple Sclerosis Society, in the United States.

"There is growing evidence linking vitamin D and risk of MS," O'Looney said. "Further studies are certainly needed to see if vitamin supplementation could reduce the risk of MS. There is insufficient evidence that vitamin supplementation can influence the course of MS once it's begun."

More information

Visit the National Multiple Sclerosis Society for more on MS.

SOURCES: Patricia O'Looney, Ph.D., vice president, Biomedical Research, National Multiple Sclerosis Society, New York City; Heather E. Hanwell, doctoral candidate, department of nutritional sciences, University of Toronto

Childhood Sun Exposure May Lower Multiple Sclerosis Risk

By Judith Groch, Senior Writer, MedPage Today
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco
July 24, 2007

LOS ANGELES, July 24 -- Exposure to the sun may be a risk factor for skin cancer, but it seems to have a protective effect against multiple sclerosis, according to a twin study.

Action Points
Explain to patients who ask that in this study of genetically identical twins, the twin who spent more time in the sun as a child, had a lower risk of developing multiple sclerosis.

Explain to patients that the cause of multiple sclerosis is unknown, but that this study may provide insight into potential avenues for future research.

In a study of 79 pairs of monozygotic twins, the twin who spent more hours outdoors as a child had a 25% to 57% reduced risk of developing MS, Thomas M. Mack, M.D., M.P.H., of the University of Southern California, and colleagues, reported in the July 24 issue of Neurology.

Despite a strong genetic component, with an approximately 20% concordance among identical twins, environmental effects have been suggested by the role of latitude and of migration within genetically uniform groups, the researchers said.

To eliminate genetic confounding, the researchers sought twins, at least one of whom had MS, by yearly newspaper advertisements throughout North America from 1980 through 1992. Diagnosis was verified by updated medical documentation through 2005.

The analysis was limited to monozygotic twin pairs in which only one of the pair had MS and their childhood exposure to the sun differed. The twins had ranked themselves before 1993 in relation to each of nine childhood sun-exposure activities.

The diagnoses of the twin cases occurred between the ages of 15 and 50, with roughly two-thirds diagnosed from age 20 to 40.

Sun exposure included nine activities, those in the four major seasons, on hot and cold days, and time spent sun tanning, at the beach, or playing team sports. A sun exposure index was calculated as the sum of those exposures for which one twin ranked higher than his or her co-twin.

The odds ratio (OR) for MS ranged from 0.25 to 0.57, depending on the activity and the time of year.

For example, the risk of MS was substantially lower (OR 0.40, 95% CI 0.19 to 0.83, P=0.06) for the twin who spent more time sun tanning than for his or her sibling. For twins who spent more time playing team sports, the OR was 0.44 (CI, 0.19-1.02, P=0.06).

For each unit increase in the sun index, the relative risk of MS decreased by 25%, independent of birthplace and age at diagnosis, the researchers said.

The protective influence was seen among female twins only, they noted, but added that this novel finding must be viewed with caution because only 13 male pairs were involved in the study.

Exposure to sunlight might induce protection against an autoimmune disease by any of several immunosuppressive mechanisms, the researchers said. Ultraviolet radiation may exert its effect directly by producing cytokines, and reducing natural killer cell activity, thus affecting innate immunity.

Ultraviolet radiation can also act indirectly by producing vitamin D and suppressing melatonin secretion, with the resultant effects on Th1-Th2 balance, they speculated.

This effect is probably achieved by activated vitamin D suppressing production of cytokines associated with MS activity, such as IL-2, and tumor necrosis factor alpha, and stimulating opposing cytokines, the researchers said.

Because the researchers used relative exposure within pairs and were unable to directly quantify exposure, they could not estimate the level of exposure that might confer protection, and such estimates would be inaccurate under any circumstances, they said.

Furthermore, estimates of "time spent in the sun" or "in outdoor activities" involve substantial recall bias, given the long interval between sun exposure and diagnosis, the researchers said.

This study, Dr. Mack and his colleagues wrote, reports the importance of sun exposure among individuals with identical genetic risks. "Studies of the pathway by which sun exposure reduces MS risk should receive high priority if we are to unravel the mystery of MS etiology," they concluded.

The authors reported no conflicts of interest. The study was supported by grants from the National Multiple Sclerosis Society, the National Institute of Neurological Disorders and Stroke, the National Cancer Institute, and the National Institute of Environmental Health Sciences.

Additional Multiple Sclerosis Coverage

Primary source: Neurology
Source reference:
Islam T et al "Childhood sun exposure influences risk of multiple sclerosis in monozygotic twins" Neurology 2007; 69: 381-388