Vitamin D insufficiency in Japanese populations: from the viewpoint of the prevention of osteoporosis.

Low levels of vitamin D nutrition (i.e., vitamin D insufficiency), which potentially cause osteoporosis, have been recognized as a common health problem for elderly people in European and North American countries, but there have been no studies on the prevalence of vitamin D insufficiency in Japan until recently. The aim of this article was to review descriptive features of serum 25-hydroxyvitamin D [25(OH)D] levels and vitamin D insufficiency in Japanese subjects. Reviewing 15 studies pertaining to vitamin D nutritional status recently published for various Japanese populations revealed that: (1) the prevalence of vitamin D insufficiency in active elderly people was as low as 5% or less; (2) the prevalence of vitamin D insufficiency was much higher (up to about 50%) in inactive elderly people than in active elderly people, depending on activities of daily living (ADL); (3) frequent fish consumption helps increase serum 25(OH)D concentrations, especially in winter; and (4) vitamin D nutrition in young women was poorer than people in middle and advanced ages, which may adversely affect bone metabolism. Future studies should focus on the effects of low vitamin D status on bone mass and fractures in Japanese subjects.