VITAMIN-D METABOLISM IS ALTERED IN ASIAN INDIANS IN THE SOUTHERN UNITED-STATES - A CLINICAL RESEARCH-CENTER STUDY

Asian Indians who immigrate to northern Europe have lower serum 25-hyd roxyvitamin D [25(OH)D] than Caucasians, and they develop vitamin D de ficiency, rickets, and osteomalacia. We investigated vitamin D metabol ism, the effects of 25(OH)D, on vitamin D metabolism and activity of 2 5(OH)D-24-hydroxylase, the rate-limiting enzyme for degradation of 25( OK)D, from cultured skin fibroblasts of Asian Indians and compared the m with cultured skin fibroblasts of Caucasians in the southern United States. Normal subjects, ages 20-40 yr, were admitted to a metabolic w ard for 2.5 days and given a daily diet containing 400 mg calcium and 900 mg phosphorus. Serum vitamin D, serum 25(OH)D, urinary calcium, an d urinary phosphorus were significantly lower, whereas serum immunorea ctive intact parathyroid hormone (PTH) and serum 1,25-dihydroxy vitami n D [1,25(OH)(2)D] were significantly higher in Asian Indians than in Caucasians. Administration of 25(OH)D-3 increased serum 25(OH)D and ur inary calcium but did not change serum PTH or serum 1,25(OK)(2)D in As ian Indians. In cultured skin fibroblasts, E-max and V-max of 25(OH)D- 24-hydroxylase activity were significantly higher in Asian Indians. In summary, in Asian Indians serum vitamin D and 25(OH)D are markedly re duced, altered vitamin D metabolism is only partially reversed by 25(O H)D-3, and 25(OH)D-24-hydroxylase activity in cultured skin fibroblast s is markedly increased. Thus, Asian Indians residing in the U.S. are at risk for developing vitamin D deficiency, rickets, and osteomalacia .