Identifying the association between depression and constipation: An observational study and Mendelian randomization analysis.

Background: Both depression and constipation are universal disorders that seriously affect quality of life. But the phenotypic relationship and causality between depression and constipation are still unclear.

Methods: We first assessed phenotypic relationships by logistic regression analysis using large-scale data extracted from the National Health and Nutrition Examination Survey (N = 11,585). We then evaluated causality by bidirectional two-sample mendelian randomization (MR) analysis using Genome-wide association study (GWAS) data (depression: N = 807,553; constipation: N = 377,277). To investigate whether depression severity affects the causal relationship between depression and constipation, we conducted a further MR study on GWAS data of major depression (N = 480,359).

Results: About 11.31 % of the participants in the constipation group suffered from depression, which was significantly higher than the normal bowel group (6.09 %). The observational study showed a positive correlation between depression and constipation (OR = 1.968, 95%CI = 1.530-2.532). Besides, the risk of constipation was higher in participants with severe depression (OR = 2.294, 95%CI = 1.538-3.422) than in participants with mild depression (OR = 1.549, 95%CI = 1.242-1.932). Bidirectional MR analysis revealed an obviously causal effect of depression on constipation, but no causal effect of constipation on depression. In addition, the MR analysis also revealed a causal relationship between major depression and constipation.

Limitation: The exact mechanism by which depression affects constipation is still unclear.

Conclusion: This study reveals a positive correlation between depression and constipation and the causal effect of depression on constipation. Clinicians should keep the risk of constipation in mind when treating patients with depression.