Sleep characteristics and cardiovascular events in a large Swedish cohort

Limited evidence suggests that the association between sleep duration and cardiovascular events is strongest in individuals who also report sleep disturbances. We investigated sleep duration and insomnia symptoms in relation to incident cardiovascular events in the Swedish National March Cohort comprising 41,192 adults. Habitual sleep duration and difficulty falling asleep, difficulty maintaining sleep, early morning awakening, and nonrestorative sleep were self-reported in 1997. During 13.2 years of follow-up, we identified 4,031 events (myocardial infarction, stroke, heart failure, or death from cardiovascular disease) in the Swedish National Patient Register and the Cause of Death Register. After adjustment for potential confounders, short sleep duration (a parts per thousand currency sign5 h) was associated with slightly increased risks of overall cardiovascular events and, specifically, myocardial infarction: hazard ratio, HR (95 % confidence interval) 1.24 (1.06-1.44) and 1.42 (1.15-1.76), respectively. These HRs were attenuated as we included BMI, depressive symptoms and other relevant covariates in our analysis. Insomnia symptoms per se were unrelated to risk. However, in a joint analysis, there was some evidence that short sleepers who reported frequent insomnia symptoms had the highest HRs (1.26-1.39) of overall cardiovascular events. Short sleep or insomnia symptoms without the other conferred no increased risk. Our results suggest that symptoms of sleep disturbance should be taken into account when assessing the association between short sleep and cardiovascular disease.