Vitamin D and prevention of osteoporosis: Japanese perspective.

Vitamin D insufficiency or a low vitamin D status, is a prevalent condition worldwide. However, there have been no studies addressing this public health issue until recently. In this review article, a summary of a series of studies conducted by the author and his colleagues to determine whether the vitamin D status of Japanese people is adequate and how their vitamin D status affects bone mass and bone metabolism is presented. The observational studies conducted by our group revealed that vitamin D insufficiency does not seem to be a serious problem among active elderly people, but that elderly people with a low level of activities of daily living (ADL) are at a very high risk of vitamin D insufficiency. In young adults, a high intact PTH concentration due to vitamin D insufficiency, which adversely affects their bone mass, is common, suggesting that vitamin D nutrition, as well as dietary calcium intake, should be improved. However, the effects of vitamin D insufficiency among elderly Japanese on bone metabolism, bone mass, and fractures have not been clarified, and should be studied further to determine whether specific preventive strategies, such as vitamin D supplementation, are required for this high-risk group. Intervention studies targeting Japanese populations are required to further address this issue.