[Vitamin D and osteoporosis: current topics from epidemiological studies].

Increases of fracture or bedridden and mortality rates associated with fracture are serious social problems in Japan. Therefore, not only the treatment but also the prevention of osteoporosis is important for the benefit of individual QOL and also to reduce the financial burden on society. Vitamin D plays an important role in the regulation of calcium homeostasis and bone metabolism. Among vitamin D metabolites, the serum 25-hydroxyvitamin D (25-D) concentration is the best indicator to assess the vitamin D status. It is known that a mild decrease in the serum 25-D concentration (vitamin D insufficiency) leads to secondary hyperparathyroidism, which has a negative effect on bone metabolism in the elderly. Therefore, vitamin D insufficiency is thought to be one of the risk factors of osteoporosis. Vitamin D insufficiency is common throughout the world. In Japan, we have also confirmed that around half of elderly women show vitamin D insufficiency. Recently, several meta-analyses of vitamin D supplementation to prevent fracture and bone loss in elderly people have been reported. In the present study, current epidemiological studies on the vitamin D status and prevention of osteoporosis, and the requirement of vitamin D to prevent osteoporosis are reviewed.