Studies of osteoporosis in Japan

Calcium deficiency appears to play a central role in the development of involutional osteoporosis, especially in Japan, where calcium intake has been traditionally low, never reaching the current recommended daily allowance (RDA) of 600 mg/d. Compromised 1,25(OH)2 vitamin D synthesis in the aging kidney and age-bound changes of the intestine itself lead to calcium malabsorption; in addition, decreasing dietary intake of fat-soluble vitamins and reduced solar exposure associated with inadequate physical activity may contribute to calcium deficiency in old age. High salt intake and increasing protein and phosphate intake tend to aggravate such a tendency. These factors appear to underlie, in part, the widespread use of vitamin D derivatives for the treatment of osteoporosis in Japan. In 1981, a large-scale, double-blind clinical trial established the superior effect of 1 alpha(OH) vitamin D3 in maintaining bone density over that of placebo. The effect of 0.5 micrograms/d 1,25-(OH)2D3 (calcitriol) in two divided doses compared favorably with that of 1 micrograms/d of 1 alpha(OH) vitamin D3 in a recently conducted multicenter, double-blind study on 596 patients with involutional osteoporosis. Spinal fracture rate was also reduced to one-half by administration of the vitamin D derivative for 1 year to 800 patients with osteoporosis.