Clinical Question: Does supplemental vitamin D increase bone mineral density?
Bottom Line: Not only does supplemental vitamin D not prevent fractures, it also does not have any meaningful effect on bone mineral density (BMD). (LOE = 1a-)
Study Design: Meta-analysis (randomized controlled trials)
Funding: Government Allocation: Unknown
The authors searched 3 databases for randomized trials that evaluated the effects of vitamin D on BMD. They point out that no meta-analysis has found vitamin D to prevent the (more important) outcome of fractures, and that BMD correlates poorly with fractures. So, they decided to study vitamin D’s effect on the irrelevant outcome of BMD and Lancet chose to publish it. Go figure. Anyway, the authors did a pretty good job on the methods: independent assessment of study eligibility, data extraction, and quality assessment. When discrepancies arose, the authors resolved them through discussion. They also assessed the potential for publication bias graphically and statistically. Ultimately, they included 23 studies with nearly 4100 patients. The studies lasted an average of 2 years. The daily vitamin D doses generally ranged from 100 international units (IU) to 2000 IU. A couple of studies evaluated 20,000 IU to 50,000 IU weekly and 2 studies evaluated 300,000 IU per year. As one might imagine, the studies also evaluated several different sites: femur, hip, trochanter, lumbar spine, forearm. Six of the studies reported that vitamin D increased BMD, 2 reported the vitamin decreased BMD, and the remainder found no overall benefit. The authors pooled the data and reported a small increase in femoral neck BMD, but no increase for any other site. The authors identified publication bias in favor of studies reporting positive results for femoral neck and hip BMD. This bias casts suspicion on the sole finding in this meta-analysis.
Henry C. Barry, MD, MS
Michigan State University
East Lansing, MI