Changes in markers of bone turnover following urbanisation of black South African women

Abstract

Objectives: To investigate dietary changes occurring with urbanisation of black South African women of different ages and how these changes influence biochemical markers of bone turnover. Design: Biochemical markers of bone turnover and resorption were determined in a subset of subjects living in the North West province of South Africa (one rural and one urban area). Women aged 15 - 25 years and 55 - 65 years were included. Food intake was measured using food frequency questionnaires. Biochemical markers were correlated with relevant changes in dietary intake that occurred with urbanisation. Results: Major findings included a significant increase in intake of animal protein, combined with very low calcium intake (< 400 mg/day). Bone turnover decreased with urbanisation as measured using osteocalcin, and bone resorption increased with urbanisation as measured with Ntelopeptides from type 1 collagen (NTx), while bone formation stayed constant. These findings were prominent in the group of active growing girls (aged 15 - 25 years). Significant negative correlations were found between NTx and body mass index (BMI), indicating the protective effect of higher BMI on bone mass. Urinary calcium was significantly positively correlated with dietary protein, calcium/protein ratio and with fibre intake. Conclusions: The changes in biochemical markers were clearer in the younger group of women and changes in diet with urbanisation seemed to have an impact on this group. Changes in bone accretion at adolescence can compromise bone strength during menopause and ageing as peak bone mass should be attained at the end of adolescence and up to age 30 years.