Biochemical markers of bone turnover and their relation to forearm bone mineral density in persons of Pakistani and Norwegian background living in Oslo, Norway: The Oslo Health Study

OBJECTIVE: To evaluate whether Pakistanis have increased bone turnover compared with ethnic Norwegians due to their high prevalence of vitamin D deficiency and secondary hyperparathyroidism, and whether the relation between bone turnover and bone mineral density (BMD) differs between Pakistanis and ethnic Norwegians. DESIGN: A cross-sectional, population-based study conducted in the city of Oslo in 2000-2001. Random samples of 132 community-dwelling Pakistani men and women of ages 40, 45, and 59-60 years, and 580 community-dwelling Norwegian men and women of ages 45 and 59-60 years are included in this substudy. METHODS: Venous serum samples were drawn for measurements of markers of the vitamin D endocrine system and the bone turnover markers osteocalcin (s-OC), bone alkaline phosphatase (s-bone ALP), and tartrate-resistant acid phosphatase (s-TRACP). BMD was measured at the forearm by single-energy X-ray absorptiometry. RESULTS: Pakistanis had higher s-bone ALP compared with Norwegians. Mean (95% CI) age-adjusted levels were 22.5 (21.0, 24.1) U/l in Pakistani men versus 19.3 (18.6, 20.1) U/l in Norwegian men, P < 0.0005, and 20.3 (18.4, 22.1) U/l in Pakistani women versus 16.7 (16.0, 17.4) U/l in Norwegian women, P = 0.001. There tended to be an inverse association between bone turnover and BMD in men and women of both ethnic groups, and it was strongest for s-bone ALP. Overall mean (95% CI) distal BMD decrease was -16 (-20, -11) mg/cm(2) per 1 s.d. increase in s-bone ALP (P < 0.0005) when adjusting for age, sex, and ethnicity. CONCLUSIONS: Except for somewhat higher s-bone ALP levels in Pakistanis, there were only minor ethnic differences in bone turnover, despite a strikingly different prevalence of secondary hyperparathyroidism. Bone turnover was inversely associated with forearm BMD in both ethnic groups.