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By Jacquelyne Froeber

THURSDAY, Feb. 5, 2009 (Health.com) — Children who lack vitamin D in the womb or in early childhood may be more susceptible to developing multiple sclerosis (MS) later in life, according to a study that suggests the vitamin helps control an MS-associated gene. The findings were published in the February 6 issue of the journal Public Library of Science (PloS) Genetics.

The findings could explain why MS, an autoimmune condition in which the body mistakenly attacks brain tissue and nerves, is relatively rare in countries near the sunny equator. MS is much more common in the darker and gloomier northern latitudes (and far southern latitudes).

Other studies have suggested that people with MS were more likely to have been born in the spring (with the bulk of pregnancy during the dark winter months) than in the fall. Sunlight is the main source of vitamin D, although it’s also found in salmon, mackerel, tuna fish, and as an additive to milk and other products.

“It’s a phenomena found over and over again,” says Moses Rodriguez, MD, a professor of neurology at the Mayo Clinic in Minnesota, who was not involved in the new research. “This study provides some link that vitamin D may be one of the environmental factors that predisposes people to MS.”

No one really knows the exact cause of MS, but researchers suspect it’s a combination of genes and environmental factors. About 2.5 million people worldwide have MS.

In the study, researchers from the University of Oxford and the University of British Columbia looked at a gene variant known as DRB1*1501, which is associated with MS. About 1 in 100 people who inherit two copies of the gene (one from each parent) develop MS, compared to 1 in 300 who have only one copy and 1 in 1,000 of those in the general population.

The researchers found that proteins activated by vitamin D bind to a DNA sequence next to the DRB1*1501 variant, which switches the gene on. If too little vitamin D is present, the gene may not function properly, which may cause a susceptibility to MS.

“We were surprised to find the [vitamin] D connection,” says study coauthor George Ebers, action research professor of clinical neurology at the University of Oxford. “We suspect women who are planning to have children may benefit from taking D in regions where they are likely to be deficient.”

There is no proof that vitamin D will prevent, treat, or cure the disease. However, the researchers suspect that a lack of vitamin D during early life may prevent the thymus, an immune system gland that sits on the top of the heart, from deleting harmful white blood cells.

These cells, known as T cells, may go on to attack the central nervous system and damage myelin, the insulation that protects nerves. In MS, this abnormal immune response affects nerve impulses to and from the brain. Symptoms of MS include numbness in the limbs, pain, coordination problems, vertigo, and vision impairment, depending on the nerves that are affected.

To prevent a vitamin D deficiency, Dr. Rodriguez recommends that his patients with MS drink up to five glasses of milk a day, depending on sunlight exposure. “We have gone from a milk-drinking society to a Coke and Pepsi society,” Dr. Rodriguez says. “The incidence of MS has been going up, and this may be one of the reasons.”

If you’re looking for a vitamin D fix, get out in the sun—and expose children to sunlight, as well. Don’t skip the sunscreen, however: Abhijit Chaudhuri, MD, PhD, a consultant neurologist and clinical lead in neurology for the Essex Centre for Neurological Sciences for Queen’s Hospital, says sunscreen should be used to protect against burns. Taking a supplement in addition to using sunblock outdoors may help maximize the health benefits, Dr. Chaudhuri says.

Dr. Rodriguez recommends a vitamin D–containing multivitamin for patients with MS and those who may be susceptible to the disease.

While an adequate vitamin D intake is good, it doesn’t mean that more of it is better or even safe, especially during pregnancy. The National Institutes of Health recommends a vitamin D intake (assuming no exposure to sunlight) that varies depending on age and gender, from 5 micrograms per day (200 International Units) in children and pregnant women to 15 micrograms (600 IU) in people 71 or older.

Too much vitamin D can be toxic, says Patricia O’Looney, PhD, vice president of biomedical research at the National MS Society in New York. “Vitamin D is a fat-soluble vitamin that the body doesn’t have the capability of getting rid of,” O’Looney says. “Excessive amounts can do damage to organs.”

O’Looney says there is still no cause or cure for MS, but technology and research in the past decade has helped to understand the disease better. “It’s an exciting time to be in genetics research,” she says. “As more therapy becomes available, we can treat patients better.”