Association between short and long sleep durations and cardiovascular outcomes: a systematic review and meta-analysis

Background: A shorter sleep duration has been identified as a risk factor for cardiovascular diseases and increased mortality. It has been hypothesized that a short sleep duration may be linked to changes in ghrelin and leptin production, leading to an alteration of stress hormone production. Here, we conducted a systematic review and meta-analysis to investigate the potential relationship between a sleep duration and cardiovascular disease mortality. Methods: We conducted a comprehensive search of Ovid Medline In-Process and other non-indexed citations, Ovid MEDLINE, Ovid Embase, Ovid Cochrane Central Register of Controlled Trials, and Scopus from database inception to March 2017. Observational studies were included if the studies reported hazard ratios or odds ratios of the associations between sleep durations (short and long) and cardiovascular disease mortality. Data were extracted by a reviewer and then reviewed by two separate reviewers. Conflicts were resolved through consensus. Using the DerSimonian and Laird random effects models, we calculated pooled hazard ratios and pooled odds ratios with 95% confidence intervals (CI). Subgroup analyses were performed to explore potential sources of heterogeneity. The quality of the included studies and publication bias were assessed. Results: In total, our meta-analysis included 19 studies (31 cohorts) with a total of 816,995 individuals with 42,870 cardiovascular disease mortality cases. In pooled analyses, both short (risk ratio 1.19; 95% CI 1.13 to 1.26, P<0.001, I-2=30.7, P-heterogeneity=0.034), and long (risk ratio 1.37; 95% CI 1.23 to 1.52, P<0.001, I-2=79.75, P-heterogeneity<0.001) sleep durations were associated with a greater risk of cardiovascular disease mortality. Conclusions: Both short (<7 hours) and long sleep durations (>9 hours) can increase the risk of overall cardiovascular disease mortality, particularly in Asian populations and elderly individuals. Future epidemiological studies would ideally include objective sleep measurements, rather than self-report measures, and all potential confounders, such as genetic variants.