Age at menarche and menopause: their correlates and association with selected cardiovascular disease risk factors among 300 000 Chinese women in the China Kadoorie Biobank

Background: Age-standardised mortality rates for cardiovascular disease (CVD) are generally higher among men than women, prompting suggestions that reproductive factors may be partly responsible. Moreover, there have been major changes in women’s reproductive patterns and CVD rates in China over the last few decades, but the association between them is still poorly understood.Objectives: To start addressing these issues, this thesis examines the secular trends and correlates of age at menarche and menopause (the major physiological events defining a woman’s reproductive window), as well as their association with blood pressure and anthropometry in 302 180 women born in 1930-74 from 10 areas across China using cross-sectional demographic, behavioural, physical and reproductive data from the China Kadoorie Biobank.Results: Mean age at menarche decreased by 2 years over a 44-year period (1930-1974), with the exception of an increase of about 1 year for women exposed to the Great Chinese Famine in early adolescence. No other factor showed as large an effect on age at menarche. Among women aged >57 years at the baseline, mean age at menopause increased by 1.4 years over a 21-year period (1930-1951) and was significantly associated with several reproductive and behavioural factors, notably gravidity (2 years later menopause) and smoking (6 months earlier menopause). Blood pressure and anthropometry were weakly inversely associated with age at menarche (0.2mmHg and 0.2kg/m² lower per year later menarche) and even more weakly positively associated with age at menopause (0.06mmHg and 0.04kg/m² higher per year later menopause). These trends and associations all varied to some extent by area and socioeconomic status. (All p-values <0.0001)Conclusion: This study adds new information on the secular trends and correlates of age at menarche and menopause in a large Chinese population born around the mid-20th century and provides a basis for further prospective work on the association of reproductive history with the incidence of CVD in China.