Sex Differences in the Association between Night Shift Work and the Risk of Cancers: A Meta-Analysis of 57 Articles

Abstract

Objectives To identify the association between night shift work and the risk of various cancers with a comprehensive perspective and to explore sex differences in this association. Methods We searched PubMed, Embase, and Web of Science for studies on the effect of night shift work on cancer, including case-control, cohort, and nested case-control studies. We computed risk estimates with 95% confidence intervals (CIs) in a random or fixed effects model and quantified heterogeneity using the I 2 statistic. Subgroup, metaregression, and sensitivity analyses were performed to explore potential sources of heterogeneity. Contour-enhanced funnel plots and the trim and fill method were used together to analyze bias. Linear dose–response analysis was used to quantitatively estimate the accumulative effect of night shift work on the risk of cancer. Results Fifty-eight studies were eligible for our meta-analysis, including 5,143,838 participants. In the random effects model, the pooled odds ratio (OR) of cancers was 1.15 (95% CI = 1.08–1.22, P < 0.001; I 2 = 76.2%). Night shift work increased the cancer risk in both men (OR = 1.14, 95% CI = 1.05–1.25, P = 0.003) and women (OR = 1.12, 95% CI = 1.04–1.20, P = 0.002). Subgroup analyses showed that night shift work positively increased the risk of breast (OR = 1.22, 95% CI = 1.08–1.38), prostate (OR = 1.26, 95% CI = 1.05–1.52), and digestive system (OR = 1.15, 95% CI = 1.01–1.32) cancers. For every 5 years of night shift work, the cancer risk increased by 3.2% (OR = 1.032, 95% CI = 1.013–1.051). Conclusion This is the first meta-analysis identifying the positive association between night shift work and the risk of cancer and verifying that there is no sex difference in the effect of night shift work on cancer risk. Cancer risk increases with cumulative years of night shift work.

Shift Work and Prostate Cancer: An Updated Systematic Review and Meta-Analysis

“…However, summary measurements must be considered with caution, due to the high heterogeneity found, the high proportion of studies with low-medium methodological quality, and the possibility of publication bias. As we have previously mentioned, other authors have also tried to summarize available evidence [27][28][29][30][31][32][33], as shown in online Supplementary Table S1.…”

“…Wendeu-Foyet et al [32] and Salamanca-Fernández et al [33] only developed a systematic review, without including a meta-analysis with the corresponding heterogeneity analysis. The meta-analyses by Rao et al, [29], and Liu et al [30] only considered fixed night-shift work as the exposure variable, without considering rotating shift work. This explains the lower number of studies they included.…”

“…From an epidemiological perspective, a number of observational studies have tried to evaluate the association between shift work and prostate cancer, although their results do not always point in the same direction [25,26]. This has led to the conduction of several reviews and meta-analyses on this topic, albeit again with inconsistent results [27][28][29][30][31][32][33]. A detailed analysis reveals that they have significant methodological weaknesses, such as high unexplained heterogeneity [28], partial inclusion of the evidence due to restrictions based on study design [27] or type of exposure (i.e., restricted to permanent night jobs), or the absence of consideration of potential publication bias [32].…”

“…Briefly, some reviews did not include different designs but cohort studies [27], however, it has been suggested that well designed case-control studies may provide more evidence than cohort studies with poor control of biases [34]. Other studies did not consider rotating work as exposure variable [29][30][31]. The consideration of only fixed-night work as exposure explains the lower number of studies included in these reviews, although the IARC considered rotating work among circadian cycle disruptors [13].…”

Time to Show Leadership on the Daylight Saving Time Debate

“…16 DST is akin to dosing the population with a small amount of shift work due to misaligning the human circadian system with typical work schedules; we know shift work is associated with cardiovascular disease, 17 metabolic dysfunction, 18,19 and cancer. 20 DST forces our biological clocks out of sync with the inexorable rising and setting of the sun (eg, the sun clock). The harmonious link between our biological clock and the sun clock has been crucial to human health and well-being for millennia.…”