Lifetime cumulative effect of reproductive factors on ischaemic heart disease in a prospective cohort.

ABSTRACT

OBJECTIVE: This study aimed to examine the association between lifetime oestrogen exposure and ischaemic heart disease (IHD), based on the hypothesis that higher lifetime oestrogen exposure is linked to lower cardiovascular risk. METHODS: In 2004-2008, lifetime cumulative exposure to reproductive factors was assessed among postmenopausal females from the China Kadoorie Biobank using reproductive lifespan (RLS), endogenous oestrogen exposure (EEE) and total oestrogen exposure (TEE). EEE was calculated by subtracting pregnancy-related and contraceptive use duration from RLS, while TEE by adding up the same components except for lactation. Incident IHD during follow-up (2004-2015) was identified. Stratified Cox proportional hazards models estimated the HRs and 95% CIs of IHD for RLS, EEE and TEE. RESULTS: Among 118 855 postmenopausal females, 13 162 (11.1%) developed IHD during a median follow-up of 8.9 years. The IHD incidence rates were 13.0, 12.1, 12.5, 13.8 per 1000 person-years for RLS Q1-Q4, 15.8, 12.6, 11.3, 12.1 per 1000 person-years for EEE Q1-Q4 and 13.7, 12.3, 12.2, 13.4 per 1000 person-years for TEE Q1-Q4. The highest quartile (Q4) of RLS and TEE were associated with lower risks of IHD (adjusted HR (aHR) 0.95, 95% CI 0.91 to 1.00 and 0.92, 95% CI 0.88 to 0.97, respectively) compared with the lowest quartile (Q1). Longer EEE showed progressively lower risks of incident IHD (aHR 0.93, 95% CI 0.88 to 0.97; 0.88, 95% CI 0.84 to 0.93; 0.87, 95% CI 0.83 to 0.92 for Q2-Q4 vs Q1). CONCLUSIONS: Longer RLS, TEE and EEE were associated with lower risks of IHD among Chinese postmenopausal females.