Yet another meta-analysis on the topic of vitamin D supplements and bone was published online today in The Lancet (October 11, 2013). The focus of this meta-analysis by New Zealand Professor Ian Reid and colleagues was changes in bone mineral density with vitamin D supplementation.
They identified all randomized, placebo-controlled studies that assessed the effects of vitamin D supplements on bone mineral density. Randomized, placebo-controlled studies means that by chance some subjects received the active ingredient, in this case vitamin D, or sometimes vitamin D with calcium. Others got an identical imitation pill called a “placebo” that did not contain vitamin D. The data from individual studies were combined and redone in a new analysis, called a “meta-analysis.”
This meta-analysis included 23 randomized controlled trials with more than 4,000 participants, primarily white women average age of 59 years. The amount of vitamin D supplementation varied from study to study. About half of the individuals were given vitamin D doses less than 800 IU per day. Results of the meta-analysis showed a small benefit at the femoral neck region of the hip; but no effect at any other site was reported, including the total hip.
In about half of the studies in this meta-analysis, vitamin D was given in combination with calcium supplementation, which makes it difficult to distinguish between the effects of calcium versus those of vitamin D.
In an accompanying editorial, Dr. Clifford Rosen wrote, “Surprisingly, any benefit reported in bone mineral density was independent of calcium supplementation, baseline concentration of 25-hydroxyvitamin D, duration of treatment, or age. The investigators conclude that widespread vitamin D prophylaxis in healthy community dwelling adults to prevent osteoporosis is unwarranted.”
Dr. Rosen served on the Institute of Medicine (IOM) committee for the 2010 update of calcium and vitamin D. He points out that the IOM recommendation of 1200 mg of calcium and 800 IU of vitamin D for skeletal health in the elderly were based on trials of vitamin D with calcium that showed a modest reduction hip fractures and small increase in hip bone mineral density was reported.
Other Meta-analyses on Vitamin D and Fractures
Other recent meta-analyses focused fracture reduction with vitamin D supplements. Those studies found vitamin D supplementation did not provide fracture reduction. However, a higher dose of vitamin D supplementation of 800 IU or more daily in persons 65 years of age or older significantly reduced the risk of hip fracture by 30% and the risk of any nonspine fracture by 14%.
Evaluation of vitamin D supplementation and effects on bone have been sliced and diced in many more meta-analyses than the number original research studies conducted creating confusion for healthcare practitioners and consumers alike.
Bottom Line on Vitamin D Supplementation and Bone
Maintenance of vitamin D stores is essential for calcium absorption. The main mechanism of action for vitamin D is promotion of calcium absorption in the gut. Vitamin D does not directly act on bone. Therefore you still need to provide sufficient vitamin D combined with dietary calcium and, if needed, calcium supplements to maintain your bone health.