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Giving children vitamin D supplements in infancy may shear their risk of developing type 1 diabetes later in life. In an analysis of previously published studies, British researchers found significant evidence that supplements of the vitamin were associated with a 29% reduced risk of the disease.

Participants in the studies were given vitamin D supplements from birth onward, for a variable time period, and were tracked for some 15 to 30 years, according to Dr. Christos Zipitis, a pediatrician with the Stockport NHS Foundation Trust and lead author of the new paper, which appears online this week in the Archives of Disease in Childhood. Types and doses of vitamin D supplements varied, and were not always reported, but Zipitis says supplementation was roughly 10 mcg, or 400 I.U., of vitamin D daily — the amount typically found in infant multivitamins. Based on data from three case-control studies involving 6,455 participants, the new paper found that infants who were given supplements were 29% less likely to develop type 1 diabetes compared with infants who never got extra vitamin D. Zipitis, who reviewed a total of five studies, also found evidence that the vitamin's protective effect increased with larger doses and more regular supplementation. "[Our study] provides the strongest evidence to date that vitamin D might be protective against type 1 diabetes in later life," says Zipitis. "Obviously we're based on other studies, so this has come up before. The new thing with our study is the strength of the association and the confidence with which we can talk about it."

Given the limits of the available data, however, the paper was unable to say how much vitamin D the children were getting from sources other than supplementation, or whether they were deficient to begin with. But Zipitis says children who had rickets, a bone disorder caused by extreme vitamin D deficiency, "were at a much higher risk of developing type 1 diabetes — I think about three times higher than the rest of the population, which would suggest that the higher the level of vitamin D in your body, the less likely you are to develop type 1 diabetes."

Past research has come to the same conclusion. Countries with lots of sunshine, which triggers vitamin D production in the body, for example, have a lower incidence of type 1 diabetes than relatively sunless places. Studies have also shown that new cases of type 1 diabetes crop up more often in winter, when there is less sunshine all around, than in summer. In addition, says Zipitis, when doctors check vitamin D blood levels of newly diagnosed type 1 diabetes patients, they are generally lower than average. "In the U.K. and other European countries, we haven't got the right UV radiation for most of the year," he says, adding that vitamin D deficiency is a re-emerging problem in the U.K., and that doctors are seeing a resurgence of rickets in children. "With all the scares about skin cancer, when people go outside, they're covered with sunblock, which doesn't allow the conversion of UV light into vitamin D. That's where the supplements come in."

Insufficient blood levels of vitamin D have been linked to several health problems aside from rickets and type 1 diabetes, including other autoimmune diseases such as rheumatoid arthritis and multiple sclerosis, along with some rare but serious heart problems like cardiomyopathy. Indeed a host of recent studies has shown myriad benefits of taking supplements. Beyond better bone health, stronger muscles and fewer fractures in adults, research also suggests vitamin D can reduce the risk of various cancers. A study of 1,179 postmenopausal women published in the American Journal of Clinical Nutrition last year found that women who took calcium and 1,100 I.U. of vitamin D daily had 80% fewer cancers than women who took a placebo or calcium alone.

For infants, the American Academy of Pediatrics (AAP) currently recommends a supplement of 200 I.U. of vitamin D per day, starting at two months of age for breastfed babies. Once infants are weaned to vitamin-D fortified formula, however, supplements are no longer necessary.

• Sora Song