No bidirectional relationship between constipation and colorectal cancer in European and Asian populations: A Mendelian randomization study

Traditional observational studies have reported a positive association between constipation and the risk of colorectal cancer (CRC). However, evidence from other approaches to pursue the causal relationship between constipation and CRC is scarce. In the study, 2-sample Mendelian randomization analysis was conducted to investigate the potential causal relationship between constipation and CRC. Analysis of the results showed that there was no causal association between constipation and CRC, either in European populations (CRC: odds ratio [OR] = 1.00, 95% confidence interval [CI] = 0.99–1.00, P = .49; rectal cancer: OR = 0.99, 95% CI = 0.99–1.00, P = .79) or in Asian populations (CRC: OR = 1.00, 95% CI = 0.99–1.01, P = .30). Also there was no inverse causal association between CRC and constipation, either in European populations (CRC: OR = 0.10, 95% CI = 2.76E-03–3.45, P = .20; rectal cancer: OR = 0.05, 95% CI = 9.14E-07–2.64E + 03, P = .59) or in Asian population (CRC: OR = 1.18, 95% CI = 0.92–1.52, P = .20), there was no horizontal diversity in the instrumental variables in the Mendelian randomization analyses of the present study (all F statistics >10), and no heterogeneity was found in the regression analyses. The findings from bidirectional 2-sample Mendelian randomization analyses indicate that there is no evidence of a bidirectional causal association between constipation and CRC. However, further investigation is warranted through additional clinical studies and trials to thoroughly explore the association between these 2 factors.