In a related study also published in the Annals of Internal Medicine issue, the USPSTF noted that there's still no evidence to support vitamin D supplementation to prevent heart disease. Limited data suggest that high dosages can reduce the risk for all kinds of cancer, but more research is needed to draw a firm conclusion, the USPSTF said. And concern remains about proper dosing, since too much vitamin D can raise the risk for kidney and urinary tract stones.
Graham said most people should ask their doctors to test their blood levels of vitamin D to ensure they're not deficient.
"More physicians are checking vitamin D in their patients," he said. "I think there's greater awareness. At some point we have to decide what's good, what's bad, what's safe and what's not safe. I think we've learned from the last 10 years of this data, that there's still a lot we don't know about vitamin D."
Chung, also an investigator at Tufts Medical Center's Institute for Clinical Research and Health Policy Studies, said that research focusing on bone mineral density -- a measurement of bone thickness -- could be useful to further pin down correct vitamin D doses for various age groups.
"It could be a shorter trial that could enroll many more people . . . and compare a variety of doses to see which dose we could probably use to the best effect," she said. "If we use fracture as an outcome, it will take much longer and cost a lot of money to enroll a lot of subjects."
The U.S. National Library of Medicine has more on vitamin D.
SOURCES: Mei Chung, Ph.D., M.P.H., assistant director, Evidence-Based Practice Center, and investigator, Institute for Clinical Research and Health Policy Studies, Tufts Medical Center, Boston; Robert Graham
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