Ethnic variation in bone turnover in pre- and early perimenopausal women: effects of anthropometric and lifestyle factors.

Bone mineral density (BMD) and fracture rates vary among women of differing ethnicities. Little is known, however, about ethnic variation in bone turnover. We measured serum osteocalcin (OC) and urinary N-telopeptide of type I collagen (NTX) levels in 2313 pre- or early perimenopausal women who were Caucasian (n = 1140), African-American (n = 651), Chinese (n = 247), or Japanese (n = 275) and were participating in the Study of Women's Health Across the Nation. Serum OC and urinary NTX levels were compared before and after adjustment for a series of lifestyle and anthropometric variables that can affect bone turnover. Unadjusted serum OC levels were highest in Caucasian women (P < 0.001 vs. all other groups), higher in African-American than Chinese women (P = 0.006), and similar in Chinese and Japanese women (P = 0.203) and African-American and Japanese women (P = 0.187). Unadjusted serum OC levels were 11-24% higher in Caucasians than in the other groups. Adjustment for covariates did not alter the ethnic pattern of serum OC levels. Unadjusted urinary NTX levels were statistically significantly higher in Caucasian and African-American women than in Chinese women (P < 0.001) for both comparisons). Unadjusted urinary NTX levels were higher in Caucasian than in Japanese women (P = 0.071) and higher in Japanese than in Chinese women (P = 0.055), but these differences were of borderline statistical significance. Unadjusted urinary NTX levels were 9-18% higher in African-Americans and Caucasians than in the other groups. Among Caucasians, there were significant geographic regional variations in both serum OC and urinary NTX levels, with higher levels in women from the Northeast and the Midwest than in women from California. These data demonstrate significant ethnic differences in bone turnover in pre- and early perimenopausal women. Although these differences in adult bone turnover may explain some of the known ethnic variation in BMD, ethnic patterns of adult bone turnover do not parallel patterns of BMD. Other factors, such as differences in bone accretion, are likely responsible for much of the ethnic variation in adult BMD.