Sleep duration and the risk of cancer: a systematic review and meta-analysis including dose-response relationship

Abstract

Background: The effect of sleep duration on cancer risk remains controversial. We aimed to quantify the available evidence on this relationship using categorical and dose-response meta-analyses.

Methods: Population-based cohort studies and case-control studies with at least three categories of sleep duration were identified by searching PubMed, EMBASE, and the Cochrane Library database up to July 2017.

Results: Sixty-five studies from 25 articles were included, involving 1,550,524 participants and 86,201 cancer cases. The categorical meta-analysis revealed that neither short nor long sleep duration was associated with increased cancer risk (short: odds ratio [OR] = 1.01, 95% confidence intervals [CI] = 0.97-1.05; long: OR = 1.02, 95% CI = 0.97-1.07). Subgroup analysis revealed that short sleep duration was associated with cancer risk among Asians (OR = 1.36; 95% CI: 1.02-1.80) and long sleep duration significantly increased the risk of colorectal cancer (OR = 1.21; 95% CI: 1.08-1.34). The dose-response meta-analysis showed no significant relationship between sleep duration and cancer risk. When treated as two linear piecewise functions with a cut point of 7 h, similar nonsignificant associations were found (per 1-h reduction: OR = 1.02, 95% CI = 0.98-1.07; per 1-h increment: OR = 1.003, 95% CI = 0.97-1.03).

Conclusion: Categorical meta-analysis indicated that short sleep duration increased cancer risk in Asians and long sleep duration increased the risk of colorectal cancer, but these findings were not consistent in the dose-response meta-analysis. Long-term randomized controlled trials and well-designed prospective studies are needed to establish causality and to elucidate the mechanism underlying the association between sleep duration and cancer risk.

Keywords: Cancer incidence; Categorical meta-analysis; Dose–response meta-analysis; Sleep duration.

Fig. 1

Flow chart showing the number of articles identified at each stage of the search

Fig. 2

Forest plot of association between short sleep duration and cancer risk. Box sizes reflect the weights of studies included in the meta-analysis, horizontal lines are the 95% CIs, and the summary OR is represented by the diamond. OR: odds ratio, CI: confidence interval

Fig. 3

Funnel plot of studies evaluating the association between short sleep duration and cancer risk. Dotted lines indicate 95% pseudo-confidence interval. SE: standard error; OR: odds ratio

Fig. 4

Forest plot of association between long sleep duration and cancer risk. Box sizes reflect the weights of studies included in the meta-analysis, horizontal lines are the 95% CIs, and the summary OR is represented by the diamond. OR: odds ratio, CI: confidence interval

Fig. 5

Funnel plot of studies evaluating the association between long sleep duration and cancer risk. Dotted lines indicate 95% pseudo-confidence interval. SE: standard error; OR: odds ratio

Fig. 6

Nonlinear dose–response analyses of sleep duration and cancer risk. The solid line and the long-dashed line represent the estimate odds ratios and their 95% confidence intervals. Seven hours of sleep per night was used as the reference