Sleep duration and breast cancer risk: A meta‐analysis of observational studies

Abstract

Studies on the association of short or long sleep duration with breast cancer risk have reported inconsistent results. We quantitatively assessed this association by conducting a meta-analysis based on the evidence from observational studies. In April 2013, we performed electronic searches in PubMed, EmBase and the Cochrane Library to identify studies examining the effect of sleep duration on breast cancer incidence. The odds ratio (OR) was used to measure any such association in a randomeffects model. The analysis was further stratified by confounding factors that could bias the results. A total of six studies (two case-control and four cohort studies) involving 159,837 individuals were included in our meta-analysis. Our study did not show an association between either short or long sleep duration and breast cancer risk (short sleep duration data: pooled OR 5 1.01, 95% confidence interval (CI) 5 0.90-1.14, p 5 0.853; long sleep duration data: pooled OR 5 0.95, 95% CI 5 0.86-1.04, p 5 0.251). Moreover, we did not identify any statistically significant association between sleep duration and breast cancer risk in all the subgroup analyses. In conclusion, our findings indicate that sleep duration has no effect on breast cancer risk.Breast cancer has become one of the most common cancers and is a leading cause of morbidity and mortality in women worldwide.1-3 Lifestyle factors, including alcohol consumption, weight gain and night-shift work, are reportedly associated with breast cancer risk.2,4 With societal development, sleeping patterns of the population have changed, which may affect the quality of life. Recently research has suggested a link between sleep duration and long-term health status. 5-11Two systematic reviews have indicated that both short and long sleep duration are significantly associated with an increased risk of all-cause mortality. 7,8 Moreover, several epidemiological studies have shown that sleep duration is associated with risk of diseases such as cardiovascular disease, obesity and cancer.5,6,9-11 However, the association between sleep duration and breast cancer incidence has not been confirmed by observational studies or meta-analysis.A possible reason for these inconsistent findings could be that individual studies did not have sufficient power to indicate any benefit or harm, particularly if event rates were lower than expected, thus resulting in broad confidence intervals (CIs). Wang et al. conducted a meta-analysis on the association of long sleep duration and breast cancer risk compared with a short sleep duration reference group, and found no strong evidence for any relationship. The result of this meta-analysis was published as a conference abstract. 12To gain a greater understanding of the effect of both short and long sleep duration on breast cancer risk, we performed a quantitative meta-analysis of observational studies to updates the previous meta-analysis and to evaluate the association between short and long sleep duration and breast cancer risk. Material and Methods Search stra...

Sleep duration and cancer risk in women

“…Recent meta-analyses of these data, while noting substantial heterogeneity in results, concluded that the evidence to date does not support an association between sleep duration and overall cancer risk [9,11,13]. Other than for breast and colorectal cancers, these meta-analyses, however, could not consider other site-specific risks due to the fact that there has not been more than one original study published for the other specific cancer sites.…”

Association between sleep-disordered breathing, obstructive sleep apnea, and cancer incidence: a systematic review and meta-analysis

“…Although two systematic reviews have supported an association between duration of sleep and risk of cancer [13,14], a review by Lu et al refuted an overall association [15], not excluding the existence of a positive association in specific cancer subtypes. Although most studies that assessed the association between SDB and cancer supported a positive association [16][17][18][19][20], evidence contrary to this also exists [21].…”

Self-reported sleep duration and cognitive performance in older adults: a systematic review and meta-analysis

“…For studies that used multiple short-sleep-duration groups, we selected the most extreme group for quantifying the effects of short sleep [34,35], the mode being 5 h or less ( Table 1). The same applied to long sleep, with the most common category being 9 h or more (Table 1).…”