Reproductive factors and risk of Parkinson's disease in women: A meta-analysis of observational studies

Evidence on the relationship between reproductive factors, use of oral contraceptives (OCs) and the incidence of Parkinson's disease (PD) remain inconclusive. The aim of this meta-analysis is to evaluate whether relevant reproductive factors including age at menarche, age at menopause, fertile lifespan, parity, type of menopause (surgical versus natural), and use of OCs are associated with risk of PD in women via random-effects model. PubMed and EMBASE database were used to search for case-control or cohort studies published before February17, 2017. 6 case-control and 5 cohort studies were included in the meta-analysis. The pooled relative risks (RRs) of PD risk were 1.00 (95% CI: 0.79-1.28) for use of OCs (ever versus never), 1.03 (95% CI: 0.84-1.26) for age at menarche, 0.98 (95% CI: 0.75-1.29) for age at menopause, 0.98(95% CI: 0.77-1.25) for fertile lifespan, 0.99(95% CI:0.0.79-1.25) for parity, 0.93 (95% CI:0.68-1.29) for type of menopause (surgical versus natural). In the subgroup analysis stratified by study design, age, caffeine intake and smoking, an inverse association was found between surgical menopause and risk of PD for those adjusting for caffeine intake (RR: 0.67, 95% CI: 0.45-0.99) and smoking (RR: 0.77, 95% CI: 0.63-0.94); while a positive association was found between surgical menopause and PD risk for those not adjusting for smoking (RR: 1.91, 95% CI: 1.29-2.83). In conclusion, our meta-analysis provided little epidemiological support for the role of reproductive factors in the incidence of PD. Whether surgical menopause is inversely associated with the risk of PD requires further explorations.