Research Challenges Current Beliefs About Vitamin D and Bone Health
University of Wisconsin School of Medicine and Public Health researcher Karen Hansen, MD has moved closer to settling the controversy with newly published findings.
"We have not found enough evidence to report with confidence a recommended daily allowance for vitamin D. But our findings do challenge a recent consensus paper that diagnosed vitamin D insufficiency in all individuals based only on a blood test," Hansen reported.
Hansen studied calcium absorption in postmenopausal women with vitamin D levels of 16-30 nanograms per milliliter (ng/ml) which the consensus paper says is the threshold for vitamin D insufficiency (VDI).
The women were given prescription amounts of vitamin D while maintaining their typical diets. Women underwent two calcium absorption studies, first when vitamin D was insufficient and later after correction of the vitamin insufficiency. During the study, published by the Journal of Bone and Mineral Research, Hansen discovered that the postmenopausal women increased calcium absorption by only 3% with vitamin D replenishment. Hansen says the 3% increase in calcium absorption does not translate to higher bone mass or lower risk of bone fractures, according to previously published research studies.
Hansen said it's important to note that both her research and the consensus paper looked at vitamin D insufficiency or mildly low vitamin D levels. In contrast, vitamin D deficiency indicates amounts low enough to cause serious health problems like rickets and osteomalacia, two diseases that cause soft bones and skeletal deformities.
"Our next step is to determine whether small increments in calcium absorption result in favorable changes in bone mass. We submitted a proposal to the National Institutes of Health in March to support these next investigations," said Hansen, a SMPH assistant professor of medicine and UW Health internal medicine and rheumatology physician.
According to the National Institutes of Health (NIH), 25 million adults in the U.S. have or are at risk for osteoporosis from lack of vitamin D. Studies have shown the fat-soluble vitamin is naturally present in very few foods. Sources of vitamin D include sunlight and supplements.
Date Published: 05/09/2008