Influence of reproductive factors on hip fracture risk in Chinese women.

To assess the relationships between reproductive factors and the risk of hip fractures in postmenopausal Chinese women, the authors analyzed data from a matched case-control study conducted in the Beijing metropolitan area among women aged 50 years and older. One hundred and fifty-six cases who sustained a hip fracture after minor trauma between January 1994 and May 1996 were identified from hospital records, of whom 121 could be located (78%). All cases agreed to be interviewed. Two controls were selected from the neighbors of each hip fracture case and matched to the cases by age within a 5-year range. Information on reproductive factors and potential confounders was obtained through personal interviews. Multivariate-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were computed using conditional logistic regression. Multiple imputation procedure was also employed to account for item non-response. Although univariate analyses revealed that later age at menopause, parity and breastfeeding were protective factors, only breastfeeding was statistically associated with risk of hip fracture after adjusting for potential confounding in multivariable logistic models. As compared with women with average duration of breastfeeding per child < or =6 months, women with average duration of breastfeeding per child 7-12 months, 13-23 months, and > or =24 months had odds ratios of 1.14 (95% CI: 0.48, 2.72), 0.28 (95% CI: 0.10, 0.82) and 0.34 (95% CI: 0.13, 0.92), respectively. Among parous women, 13% reduced risk was associated with every 6 months increase in breastfeeding per child. The authors conclude that extended breastfeeding is associated with a reduced hip fracture risk among Chinese women in Beijing.