Vitamin D status and markers of bone turnover in Caucasian and South Asian postmenopausal women living in the UK

Suboptimal vitamin D status among the South Asian UK population is widely reported; however, its impact on bone health is unclear. The aim of the present study was to conduct a comparative investigation of vitamin D status in postmenopausal South Asian (SA) and Caucasian (C) women and its relationship to parathyroid hormone (PTH) concentration, biochemical markers of bone turnover and bone quality. A cross-sectional study of community-dwelling women aged 50-66 years was carried out. A total of sixty-six SA women of Pakistani origin and forty-two C women living in the same community were recruited. Fasting blood was taken for the measurement of vitamin D, PTH and biochemical markers of bone turnover, including type-1 collagen beta C-telopeptide (beta CTX), procollagen type-1 amino-terminal propeptide (P1NP), and bone-specific alkaline phosphatase (BAP) activity. Bone quality was assessed using broadband ultrasound attenuation (BUA). Total serum 25-hydroxyvitamin D (25(OH)D) was significantly lower in the SA women than the C women (medians: SA 10.5 v. C 47-1 nmol/l; P<0.001) This was associated with a significantly elevated serum PTH concentration in the SA group (medians: SA 7.3 v. C 4.5 pmol/1; P<0-01). BAP activity was also significantly higher in the SA group, indicating elevated osteoblast activity and bone turnover (medians: SA 23-0 v. C 20.0U/l; P<0.05). No significant differences were observed between the two groups for P1NP, beta CTX or BUA. Although the SA women had significantly higher serum PTH and lower 25(OH)D concentrations than C women, this was not associated with significantly higher markers of bone resorption, or reduced bone quality in the SA women.