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Month of Birth May Influence Risk of MS by Promoting Changes in Immune System Development

April 15, 2013

British researchers investigated why people born in May appear to have a higher risk of developing MS than those born in November. Based on tests done on umbilical cord blood from healthy babies, they suggest that those born in May tend to have higher levels of potentially harmful immune cells and lower levels of vitamin D in their blood, and that these factors may influence MS risk. If confirmed in larger studies, this offers more evidence for the interaction of environmental and genetic factors in MS. Research is ongoing in vitamin D and other factors that may control risks for developing MS. Giulio Disanto, MD, Sreeram Ramagopalan, DPhil, and colleagues at the University of Oxford and Queen Mary University of London published their study in the April 2013 issue of the JAMA Neurology (70(4):527-8).

Background: Many factors, including genetic and environmental factors, probably affect the risk of developing MS. Vitamin D is an important nutrient that humans get from food, dietary supplements, and most importantly, from sun exposure. Research has increasingly indicated that lower levels of vitamin D in the blood are associated with a higher risk of developing MS. There have been several studies implicating a link between the month a person is born and the risk for developing MS. These studies suggest that people born in May have about a 20% increase risk of MS compared to people born in November.

The immune system is “educated” during development, both before and after birth, and this occurs in an immune organ call the thymus, located in front of the heart. When functioning properly, this thymic education determines the strength of a person’s immune response to foreign invaders like bacteria or viruses and even cancer cells. When it does not function properly, it can lead to immune dysfunctions, such as occurs in MS. The proper balance of immune activity is regulated by immune genes, but the environment likely also plays an important role.

The authors of this study speculated that the month of birth effect was due to the influence of vitamin D (less sunlight exposure of the mother and lower vitamin D levels for the babies born in May compared to November) on the education of the immune response in the thymus before birth.

The Study: To begin to test this idea, the investigators obtained umbilical cord blood from 50 healthy babies born in May and 50 healthy babies born in November, and determined thymic function by measuring specific immune cells and other immune activity. They also measured vitamin D levels. They found that babies born in May had significantly higher levels of mature immune T cells (which have been implicated in MS and other immune-mediated diseases) than babies born in November. Babies born in May also had lower levels of vitamin D, suggesting that vitamin D might play a role in thymic function.

The small number of participants and the fact that all the babies came from one city (London) make it hard to know if this observation will be universal. Larger multicenter studies would be required to confirm this team’s findings.

Comment: If confirmed, this observation could provide a rationale for giving vitamin D supplementation during pregnancy with the idea of lowering the baby’s risk for MS in the future. More evidence would be necessary before such a recommendation could be made.

The National MS Society is funding several projects in this area to test whether vitamin D can reduce disease activity in people who have MS. In 2011, the Society convened a summit  to explore vitamin D trials farther.

Chronic excess vitamin D is associated with side effects, and some people cannot take supplements, so their use should be administered and monitored in consultation with a physician.

About Multiple Sclerosis

Multiple sclerosis is an unpredictable, often disabling disease of the central nervous system. Symptoms range from numbness and tingling to blindness and paralysis, and there is currently no cure for MS. The progress, severity and specific symptoms of MS in any one person cannot yet be predicted, but advances in research and treatment are leading to better understanding and moving us closer to a world free of MS. An estimated 1 million people live with MS in the United States. Most people with MS are diagnosed between the ages of 20 and 50, and it affects women three times more than men.


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