Association between sleep traits and risk of colorectal cancer: a bidirectional Mendelian randomization study

Background: Sleep traits have been linked to diseases; particularly, their impact on cancer has received increasing attention. This study aimed to investigate whether sleep traits have a causal relationship with colorectal cancer (CRC) using two-sample Mendelian randomization (TSMR). Methods: Genetic instrumental variables (IVs) for seven sleep traits (sleep duration, ease of getting up in the morning, morning chronotype, daytime napping, insomnia symptoms, snoring, and daytime dozing) were selected from pooled data from published genome-wide association studies (GSWSs). Two-sample multivariate Mendelian randomization (MR) analyses were conducted to assess the causal association between sleep traits and CRC. Reverse MR analyses were performed to determine the causal relationship between CRC and sleep traits. Inverse variance weighted (IVW), MR-Egger, and weighted medians were calculated for all MR analyses. Results: The multivariable MR (MVMR) analysis found that appropriate sleep duration [odds ratio (OR) =0.989; 95% confidence interval (CI): 0.980, 0.999; P=0.04] and ease of getting up in the morning (OR =0.990; 95% CI: 0.980, 1.000; P=0.04) were protective factors for CRC. Snoring (OR =1.021; 95% CI: 1.002, 1.041; P=0.03) was associated with the risk of CRC. Ease of getting up in the morning (OR =0.990; 95% CI: 0.983, 0.997; P=0.003) was associated with reduced risk of colon cancer. Morning chronotype (OR =1.004; 95% CI: 1.000, 1.007; P=0.04) was associated with the risk of colon cancer. Insomnia symptoms (OR =0.995; 95% CI: 0.990, 0.999; P=0.03) were a protective factor for rectal cancer. There was no evidence found for a causal association between other sleep traits and CRC, colon, or rectal cancer. Conclusions: Proper sleep duration and ease of getting up in the morning may be protective factors against CRC, and snoring may increase the risk of CRC.