The role of vitamin D in the prevention of osteoporosis.

The need for vitamin D to prevent rickets was the drive for selection of lighter skin color in temperate climates. Anthropologists also know that as human populations developed more sedentary lifestyles, this coincided with a decline in bone quantity, quality, and fracture resistance. Since osteoporosis occurs after the reproductive years, there is no way that natural selection could have adapted our biology to prevent it. However, osteoporosis can be largely prevented by optimizing physical activity, and the vitamin D-related factors of environment, and nutrition. The role of vitamin D3 in osteoporosis is conclusively established from a very simple meta-analysis of the four randomized, placebo-controlled clinical trials into the effect of 20 microg (800 IU) per day. These have all demonstrated that this dose prevents approximately 30% of hip or non-vertebral fractures compared to placebo, in adults older than 65 years. Intakes less than this have never been found effective. The lowest average serum 25-hydroxyvitamin D concentration in any study demonstrating fracture reduction was 74 nmol/L. Thus, 25-hydroxyvitamin D levels in older adults should exceed this amount. The role of vitamin D supplementation is to provide humans with the nutrient in an amount closer to our species' biological norm. This amount of vitamin D results in the optimal function of many aspects of health, including balance and muscle strength that lessen the risk of fracture beyond what is possible via the quality and quantity of bone itself.