Severe
vitamin D deficiency may cause
rickets. While this point is not disputed, the use of
vitamin D in the elderly to prevent fractures has been challenged recently by a meta-analysis of 81 RCTs, suggesting that the effects of
vitamin D were trivial. As is true for any review of the literature, the interpretation of a meta-analysis can be confounded by the choice of publications to include or exclude. Indeed, the authors excluded RCTs with combined
vitamin D and
calcium supplementation, included futile studies of very short duration, or studies with high bolus doses known to transiently increase fracture risk. The best available data show that
calcium and
vitamin D supplementation of elderly subjects can decrease the risk of hip and other non-vertebral fractures, especially in institutionalized subjects or elderly subjects with poor
calcium and
vitamin D status.
Vitamin D deficiency is associated with many
chronic diseases. The VIDA and VITAL trials did not show a protective effect on
cardiovascular diseases and
cancer. The D2d study also did not influence the progress of
prediabetes to diabetes. However, the baseline 25OHD concentrations of the majority of the participants of all these trials were essentially normal. Post-hoc analysis of these studies suggest some possibly beneficial health outcomes in
vitamin D deficient subjects. A meta-analysis suggested that
vitamin D could partly prevent
upper respiratory infections. Mendelian randomization studies suggest a causal link between lifelong low
vitamin D status and
multiple sclerosis. A
vitamin D supplement in pregnant women may decrease maternal morbidity and improve the health of their offspring. Better-designed studies are needed to answer all outstanding questions. However, based on all available data, it seems that correction of
vitamin D and/or
calcium deficiency of infants, pregnant women and elderly subjects can improve their health. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and
Mineral Research.