Serum 25-hydroxyvitamin D and muscle atrophy in the elderly.

The objective of this review is to consider the mechanisms by which vitamin D affects muscle and the evidence that vitamin D status is important for muscle performance and fall prevention in older adults. Vitamin D receptors have been identified in human skeletal-muscle cells. Activation of these receptors by 1,25-dihydroxyvitamin D is involved in the action of vitamin D on the myocyte. Several studies have examined the effect of supplemental vitamin D on muscle strength, balance and falls. Among those examining muscle strength, results have been either positive for vitamin D or null. A recent meta-analysis of seventeen such trials revealed no significant effect of vitamin D overall, but a significant improvement in strength was observed in the trials in which the mean starting level of 25-hydroxyvitamin D was 25 nmol/l or below. Evidence for an effect of vitamin D on balance, measured as sway, is less abundant but more consistently positive. Many trials have evaluated the effect of supplemental vitamin D on falls. Overall, there is about a 20% lower risk of falling with supplementation. One meta-analysis considered the vitamin D dose administered and concluded that doses up through 15 μg (600 IU) were ineffective and doses of 17·5-25 μg/d (700-1000 IU/d) significantly lowered fall risk. The minimal 25-hydroxyvitamin D level needed for benefit was 60 nmol/l.