Daytime napping and mortality from all causes, cardiovascular disease, and cancer: a meta-analysis of prospective cohort studies

Objectives: The association between daytime napping and mortality remains controversial. We conducted a meta-analysis to examine the associations between daytime napping and the risks of death from all causes, cardiovascular disease (CVD), and cancer. Methods: PubMed and Embase databases were searched through 19 September 2014. Prospective cohort studies that provided risk estimates of daytime napping and mortality were eligible for our meta-analysis. Two investigators independently performed study screening and data extraction. A random-effects model was used to estimate the combined effect size. Subgroup analyses were conducted to identify potential effect modifiers. Results: Twelve studies, involving 130,068 subjects, 49,791 nappers, and 19,059 deaths, were included. Our meta-analysis showed that daytime napping was associated with an increased risk of death from all causes [n = 9 studies; hazard ratio (HR), 1.22; 95% confidence interval (CI), 1.14-1.31; I-2 = 42.5%]. No significant associations between daytime napping and the risks of death from CVD ( n = 6 studies; HR, 1.20; 95% CI, 0.96-1.50; I-2 = 75.0%) and cancer (n = 4 studies; HR, 1.07; 95% CI, 0.99-1.15; I-2 = 8.9%) were found. There were no significant differences in risks of all-cause and CVD mortality between subgroups stratified by the prevalence of napping, follow-up duration, outcome assessment, age, and sex. Conclusions: Daytime napping is a predictor of increased all-cause mortality but not of CVD and cancer mortality. However, our findings should be treated with caution because of limited numbers of included studies and potential biases. (C) 2015 Published by Elsevier B.V.