Causal assessment of sleep on coronary heart disease

Sleep is an essential physiological process that protects our physical and mental health. However, the causality of the association between sleep and coronary heart disease (CHD) is unknown. Mendelian randomization (MR), using genetic variants as instrumental variables to test for causality, can infer credible causal associations. We applied a two-sample MR framework to determine the causal association between sleep (sleeplessness, sleep duration, and daytime dozing) and CHD by integrating summary-level genome-wide association study (GWAS) data. Data included in this study were the GWAS summary statistics datasets from the C4D Consortium for CHD; Neale Lab UKB-a:13 Consortium for sleeplessness; Neale Lab UKB-a:9 Consortium for sleep duration and Neale Lab UKB-a:15 Consortium for daytime dozing. The conventional MR approach (inverse variance weighted, IVW) method and Egger method were used. Heterogeneity was calculated using each of the different MR methods where possible. Horizontal pleiotropy was evaluated by p-value of the MR–Egger intercept. The IVW method estimate indicated that the odds ratio (OR) (95% confidence interval, CI) for CHD was 3.924 (1.345–11.447) per standard deviation increase in sleeplessness (p = 0.012). Results were consistent in MR–Egger method (OR, 4.654; 95% CI, 1.191–18.186; p = 0.009). The genetically predicted sleeplessness was positively casually associated with CHD. The causal association between sleep duration (or daytime dozing) and CHD was not established. Our analysis provided evidence supporting a causal relationship between sleeplessness (not sleep duration or daytime dozing) and CHD.