THE EFFECT OF AGING ON BONE-MINERAL METABOLISM AND BONE MASS IN NATIVE-AMERICAN WOMEN

OBJECTIVE: To examine the effect of age on mineral metabolism and bone mineral density (BMD) of the hip and spine in Native American women. DESIGN: A cross-sectional study. SETTING: The Sac and Fox Nation in ru ral Oklahoma MEASUREMENTS: Serum measurements were made of 25 hydroxyv itamin D (25OHD), osteocalcin, and immunoreactive parathyroid hormone. Bone mineral density of the hip and spine was assessed by dual energy X-ray absorptiometry. PARTICIPANTS: A total of 77 Native American wom en aged 19 to 85 years. RESULTS: Serum 25 hydroxyvitamin D was related inversely to age (r = -0.32; P < .05) and was less than 15 ng/mL in 7 % of the subjects. Serum osteocalcin was higher (P < .001) in postmeno pausal than in premenopausal subjects. In postmenopausal subjects, ser um osteocalcin was related to age (r = .59, P < .001). BMD was lower ( P < .001) in postmenopausal than in premenopausal subjects. There was no evidence of bone loss before age 50 in either the femur or the spin e. Age (r greater than or equal to -0.48, P < .001) and body mass inde x (BMI) (r greater than or equal to 0.41, P < .005) were independent d eterminants of both femoral and lumbar BMD. Serum 25OHD was a signific ant independent determinant of both lumbar (r = .26, P < .05) and femo ral (r = .41, P < .01) BMD. Age, BMI, and serum 25OHD together account ed for 70% of the variance in BMD at these sites. The use of t scores indicated femoral bone density was higher (P < .05) in premenopausal N ative American women, and lower (P < 0.05) in postmenopausal subjects, compared with white women. CONCLUSIONS: In Native American women, the re is a reduction in bone density and a sustained increase in bone tur nover postmenopausally. BMI and serum 25OHD are significant determinan ts of BMD. Peak BMD may be higher, and the postmenopausal rate of bone loss greater, than that in white women.