The Truth About Vitamin D

The D List of Illnesses

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Without enough D, babies can develop rickets, which softens bones, leading to bowed legs, knock-knees, and other deformities. But healthy bones aren't the only reason children need D. "Vitamin D activates the body's immune response as well as cells that kill bacteria and viruses," explains Michael F. Holick, M.D., Ph.D., professor of medicine, physiology, and biophysics at Boston University Medical Center, and the author of The Vitamin D Solution. Earlier this year, researchers in Japan reported that schoolchildren taking a daily supplement of 1200 IU of vitamin D reduced their rate of influenza by almost half. Meanwhile, researchers from Finland have reported a strong association between vitamin D supplementation during infancy and a reduction in the risk of type 1 diabetes.

D may also reduce inflammation in various parts of the body, such as the heart and lungs. Inflammation is an underlying cause of cardiovascular disease -- which can begin in the first decades of life. It contributes to the formation of plaque in arteries, making it hard for blood to travel through vessels, raising blood pressure. Vitamin D seems to keep blood vessels flexible and helps the heart beat more efficiently. A 2009 government analysis of more than 3,500 12- to 19-year-olds linked levels below 15 ng/mL to high blood pressure, high blood sugar, and metabolic syndrome, a risk factor for heart disease. Adults with low levels are two to three times more likely to die of heart failure than those whose levels are sufficient, according to a recent Journal of Cardiac Failure study. And too little D may increase the risk of kids' asthma and worsen symptoms. Children with a D insufficiency were 50 percent more likely to have a serious asthma attack, found Harvard researchers. Adults with asthma who also have low D levels have twice the degree of airway constriction than those with higher levels.

Cancer may be D-sensitive too. "Some evidence suggests that when people have inadequate vitamin D, they're at an increased risk for colon cancer," says Cindy D. Davis, Ph.D., program director of the Nutritional Sciences Research Group at the National Cancer Institute.

D deficiency may even affect pregnancy. In preliminary research at the Medical University of South Carolina, in Charleston, pregnant women who reached ideal D levels via supplements experienced fewer complications -- including gestational diabetes and preterm labor -- compared with women who did not take them, says Carol Wagner, M.D., a pediatrician and neonatologist who led the study.

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