Menopause and risk of hip fracture in middle-aged Chinese women: a 10-year follow-up of China Kadoorie Biobank.

Objective: Bone loss is accelerated after menopause in women, as is the risk of hip fracture, but little is known about the importance of age at menopause, time since menopause, and total reproductive years for risk of hip fracture. Methods: Between 2004 and 2008, the China Kadoorie Biobank recruited 125,336 postmenopausal women who had a natural menopause and recorded 1,327 incident cases of hip fracture during the first 10 years of follow-up. Multivariable Cox regression was used to estimate hazard ratios and 95% CIs for incident hip fracture for age at menopause, time since menopause, and total reproductive years. Results: The mean (SD) age at menopause was 48.8 (4.0) years. Compared with women who reached menopause before age 53 years, women with a later age at menopause had a 22% (95% CI, 11%-35%) lower risk of hip fracture. Compared with women who were <5 years since menopause, those who were 5 to 9, 10 to 14, 15 to 19, and >= 20 years since menopause had hazard ratios of hip fracture of 1.43 (95% CI, 1.01-2.04), 2.10 (95% CI, 1.71-2.57), 2.50 (95% CI, 2.21-2.83), and 2.33 (95% CI, 1.97-2.75), respectively. Women with a longer (>= 36 y) versus shorter (<30 y) duration of total reproductive years had a 19% (95% CI, 9-28) lower risk of hip fracture. Conclusions: Women with younger age at menopause, longer interval since menopause, or shorter duration of total reproductive years had the highest risks of hip fracture.