骨粗鬆症予防とビタミンD : 第258回徳島医学会学術集会市民公開シンポジウムより

Vitamin D plays a critical role in calcium and bone metabolism. Vitamin D is supplied from intake of vitamin D rich food and sunlight exposure in skin, and subsequently metabolized to 25-hydroxyvitamin D (25OHD) in liver and to 1,25-dihydroxyvitamin D, active vitamin D, in kidney. Serum 25OHD concentration is most useful marker for estimating nutritional status of vitamin D. Although 25OHD is not active form, many epidemiological studies have clearly shown that low 25-hydroxyvitamin D (25OHD) concentrations are associated with low bone mineral density and incidence of fracture. Recently, the Japanese Society for Bone and Mineral Research and the Japan Endocrine Society have proposed the guidelines for assessment criteria for vitamin D deficiency/insufficiency using serum 25OHD concentration in Japan as follows. (1) Serum 25OHD concentration equal to or above 30 ng/ml is considered to be vitamin D sufficient. (2) Serum 25OHD concentration less than 30 ng/ml but not less than 20 ng/ml is considered to be vitamin D insufficient. (3) Serum 25OHD concentration less than 20 ng/ml is considered to be vitamin D deficient. According to this criteria, many recent studies have reported that more than 50% of Japanese people are in vitamin D deficiency defined by lower than 20 ng/mL. Declines of fish intake and sunlight exposure in recent Japanese life style would be risk factors of vitamin D deficiency. However, most people unaware their own vitamin D status. Regarding requirement of vitamin D for prevention of osteoporosis or to ensure a sufficient vitamin D status, the recommendations are not fully consistent but at least 10-20 μg (400-800 IU) of vitamin D per day can be recommended in the general. To prevent osteoporosis, nutritional self-care in vitamin D should be strongly recommended by taking vitamin D rich foods or by effective sunlight exposure.