D is for … death defying?

Why are conditions such as colon cancer, multiple sclerosis and type 1 diabetes less common in areas with plentiful sunlight? Some research points to an abundance of vitamin D, the only nutrient our bodies synthesize from sunlight. Vitamin D, it turns out, plays an important role in regulating the immune system.

It may even lengthen your life. In 2007, a study analyzing 18 clinical trials found that people who took vitamin D supplements regularly had a 7 percent lower death rate over five and a half years. "That could translate into one or two more years of life," says Philippe Autier, M.D., of the International Agency for Research on Cancer, one of the study authors. Other conditions that may be deterred by vitamin D:

• Cancer. A 2007 controlled study of nearly 1,200 postmenopausal Nebraska women linked supplements of vitamin D and calcium to a 77 percent lower risk of all cancer, but the strongest evidence is for prevention of colon cancer, according to several large-scale studies. Some studies also show possible benefits against breast, prostate and other cancers.
  
  
• Heart disease. Adequate vitamin D may help control high blood pressure and protect against heart disease, studies show.
  
  
• Multiple sclerosis (MS). Researchers at Harvard studied blood samples of military personnel and found that white Americans with the highest levels of vitamin D were 62 percent less likely to develop MS, an autoimmune neurological disease, compared to those with the lowest levels. The finding didn't extend to people of other races, though, possibly because of inadequate sample size. Another Harvard study found that women with the highest intake of dietary vitamin D had a 33 percent lower risk for MS, and women with the highest intake from supplements had a 41 percent lower risk, compared to women with the lowest vitamin D intakes from diet or supplements.
  
  
• Depression. Vitamin D deficiency has been associated with mood disorders in older people, but more research is needed before a clear link can be established. Taking vitamin D supplements has not been proven in studies to relieve symptoms of depression.
  
  
• Other conditions. There is some preliminary evidence that vitamin D may play a role in preventing some infections, rheumatoid arthritis, diabetes (type 1 and type 2), dementia and macular degeneration, a common eye disease.
  

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