The length of night shift work is closely associated with cancer risk: A pan-cancer study of Mendelian randomization study

Night shift work (NSW) has been associated with cancer risk in animal studies, but epidemiological evidence remains insufficient and contradictory. This study sought to investigate the causal association between NSW and 13 common cancers using a two-sample Mendelian randomization (MR) study. Genetic variants associated with NSW were extracted from the UK Biobank and selected as instrumental variables (IVs). Genome-wide association study (GWAS) data for 13 cancers were obtained from relevant consortia and biobanks. Causality was estimated using inverse-variance weighted (IVW), MR-Egger, and weighted median (WM). Sensitivity analyses, including MR-Egger intercept tests, MR-PRESSO, leave-one-out analyses, and funnel plots, were conducted to detect pleiotropy and heterogeneity. A suggestive causal association was found between NSW duration and risks of cervical (IVW: <i>p</i> = 0.028) and gastric cancer (IVW: <i>p</i> = 0.011). No significant associations were observed for other cancers (<i>p</i> > 0.05). These findings suggest the need to reduce NSW duration and limit nocturnal light exposure to maintain circadian rhythms and mitigate cancer risks.