Background Parity has been reported to play an important role in the development of cardiovascular disease; however, the results are still controversial. We aimed to conduct a meta-analysis of cohort studies to assess quantitatively the association between parity and cardiovascular disease risk. Methods PubMed and Web of Science databases were searched to 1 June 2018, supplemented by manual searches of the bibliographies of retrieved articles. And multivariate-adjusted relative risks were pooled by using random-effects models. Restricted cubic spline analysis with four knots was used to explore the relationship of parity and the risk of cardiovascular disease. Results Ten cohort studies involving 150,512 incident cases of cardiovascular disease among 3,089,929 participants were included in the meta-analysis. A significant association between parity and cardiovascular disease risk was observed while comparing parity with nulliparity, with a summarised relative risk of 1.14 (95% confidence interval (CI) 1.09–1.18; I2 = 62.0%, P = 0.002). In the dose–response analysis, we observed a potential non-linear J-shaped dose–response relationship between the number of parity and cardiovascular disease risk, the summary risk estimates for an increase of one live birth was 1.04 (95% CI 1.02–1.05), with significant heterogeneity ( I2 = 89.6%). In addition, the similar J-shaped associations between parturition number and cardiovascular disease, ischaemic heart disease or stroke risk were also observed. Conclusions Our findings suggest that ever parity is related to cardiovascular disease risk and there is an association between the number of pregnancies and the risk of cardiovascular disease. Since the number of included studies was limited, further studies are warranted to confirm our findings.

Background Previous studies have suggested that shift work is associated with a higher risk of cardiovascular disease. However, the quantitative dose-response relationship between duration of shift work and cardiovascular disease risk is still unknown. We aimed to evaluate the dose-response association between duration of shift work and risk of cardiovascular disease morbidity and mortality. Design A systematic review and meta-analysis. Methods PubMed and Embase were searched from inception to 1 December 2017. Prospective cohort studies that reported the associations between duration of shift work and cardiovascular disease risk with at least three categories were included. Data were pooled by using fixed or random effect models. The continuous dose-response associations were assessed by using fixed effect restricted cubic splines with four knots. Results Five prospective cohort studies with 10 reports were included. No evidence of a curvilinear association was observed between duration of shift work and risk of cardiovascular disease, similar findings were observed in cardiovascular disease morbidity and mortality. The summary relative risk (RR) of an increase of 5 years of shift work was 1.05 (1.04-1.07) with moderate heterogeneity ( P = 0.142, I= 33.2%) for cardiovascular disease, 1.06 (1.04-1.08) with low heterogeneity ( P = 0.279, I= 21.7%) for cardiovascular disease morbidity, and 1.04 (1.02-1.06) with moderate heterogeneity ( P = 0.135, I= 38.5%) for cardiovascular disease mortality, respectively. Conclusions Shift work could probably increase the risk of cardiovascular disease and cardiovascular disease mortality in a dose-response way. These findings could have implications for guideline recommendations regarding the risk related to shift schedules.

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It remains unclear how many hours of sleep are associated with the lowest risk of osteoporosis. This meta-analysis was performed to assess the dose-response relationship between sleep duration and risk of osteoporosis. PubMed and Web of Science were searched from inception to December 3, 2017, supplemented by manual searches of the bibliographies of retrieved articles. Data were pooled using fixed- and random-effects models. Restricted cubic spline analysis with four knots was used to model the sleep duration and osteoporosis association. Four cross-sectional studies with eight records were eligible for inclusion in the meta-analysis. A U-shaped dose-response relationship was observed between sleep duration and risk of osteoporosis, with the lowest risk observed at a sleep duration category of 8-9 h per day. Compared with 8-h sleep duration per day, the pooled odds ratio for osteoporosis were 1.03 (95% CI 1.01-1.06) for each 1-h reduction among individuals with shorter sleep duration and 1.01 (95% CI 1.00-1.02) for each 1-h increment among individuals with longer sleep duration. Our dose-response meta-analysis shows a U-shaped relationship between sleep duration and risk of osteoporosis, with the lowest osteoporosis risk at about 8 h per day of sleep duration. Both short and long sleep duration is associated with a significantly increased risk of osteoporosis in the middle-aged and elderly adults, appropriate sleep duration could help for delay or prevention of osteoporosis.