Vitamin D didn't increase BMD in healthy, nonelderly adults

Vitamin D supplementation doesn't improve bone mineral density (BMD) in healthy adults, a new systematic review and meta-analysis concluded.

Researchers included 23 studies with more than 4,000 participants (all without metabolic bone disease; 92% women; average age, 59 years) that assessed the effects of supplementation with vitamin D₃ or D₂ on BMD. Mean baseline serum 25-hydroxyvitamin D concentration was less than 50 nmol/L (20 ng/mL) in 8 of the studies, and in 10 studies, participants took less than 800 IU of vitamin D per day. Results were published online by The Lancet on Oct. 11.

Bone mineral density was measured at 1 to 5 sites on the body in the included studies, and according to the review, there were 6 findings of significant benefit from supplementation and 2 of significant detriment; the rest were nonsignificant. The meta-analysis found that BMD was increased by calcium supplementation at only 1 measurement point, the femoral neck, and the benefit was small (weighted mean difference, 0.8%; 95% CI, 0.2% to 1.4%). There was significant heterogeneity among the trials (I²=67%).

The results are consistent with some prior meta-analyses that have found little reduction in fractures from vitamin D supplementation, the authors said. The results do conflict with some other reviews, but those studies gave patients calcium along with vitamin D, so the effects of the 2 supplements cannot be separated. This analysis's negative findings suggest that vitamin D does not work directly on bone cells to promote mineralization and that widespread use of vitamin D supplements for adults without risk factors for vitamin D deficiency is not justified, the authors said.

Individuals who actually have vitamin D deficiency may still benefit from supplementation, and further research is needed to improve the definition of vitamin D deficiency, the researchers recommended. Some clinicians have been targeting serum 25-hydroxyvitamin D concentrations greater than 75 nmol/L (30 ng/mL), they said, noting that their research findings and the 2010 Institute of Medicine report do not support this practice. The resources currently spent on measurement and supplementation of vitamin D levels could be better spent elsewhere, they concluded.

An accompanying comment agreed with the study's findings but noted that maintenance of vitamin D in the elderly (along with sufficient calcium intake) remains appropriate for prevention of hip fractures.