A. Evidence is growing that the "sunshine vitamin" is very important to the proper functioning of the immune system. One clue to the importance of vitamin D is that cells throughout the body have receptors for the vitamin that, when activated, are important to the regulation of cell growth and division. Vitamin D is one of the most actively studied nutrients and researchers around the globe are learning that the role of this vitamin goes far beyond regulating bone health and development.
Exciting new research suggests that vitamin D may offer protection against some types of cancer, including breast and prostate cancers and, in particular, colorectal cancer. How vitamin D fights cancer isn’t known for sure, but it “helps reduce cell proliferation and differentiation, and it may reduce inflammation,” says Edward Giovannucci, M.D., professor of nutrition and epidemiology at the Harvard School of Public Health in Boston.
Research is also revealing vitamin D’s promise in autoimmune disease. For example, a sufficient level of vitamin D may confer some protection against developing multiple sclerosis (MS). Vitamin D may also play a protective role in diabetes, which is also considered an autoimmune disease since it involves immune-cell attack on the insulin-secreting cells of the pancreas. Experts are not sure about how vitamin D protects against autoimmune diseases, but believe that it may serve as a brake on the overactive immune cells.
Other, preliminary research hints at a connection between inadequate prenatal vitamin D and asthma in young children. Recent data even suggest that low vitamin D may be linked with epidemic influenza (which tends to strike, after all, during sun-deprived winter months).
Currently, the Dietary Reference Intakes (DRI) for vitamin D range from 200 to 600 international units (IU) per day, but many researchers believe 1,000 IU daily of vitamin D is optimal for most people, and that the upper limit (the amount not to exceed to avoid risk of toxicity), which is currently set at 2,000 IU per day, can safely be raised to as high as 10,000 IU per day. But vitamin D isn’t widely available in the food supply (best sources include fatty fish and vitamin-D-fortified milk, orange juice and cereals), so to achieve those levels, you’ll likely need to take a supplement.