Constipation prevalence and its association with kidney function: a large nationwide Japanese health check-up cohort study

Background: Constipation is one of the most common gastrointestinal disorders in the general population. However, its prevalence in patients with chronic kidney disease (CKD) and its association with kidney function have not been comprehensively examined. Methods: Using nationwide annual health check-ups and medical claims data collected in Japan from 2015-2023, we identified a total of 903 984 person-year observations from 217 734 unique individuals aged 20-74 years with available estimated glomerular filtration rate (eGFR) data. We evaluated the prevalence of constipation, defined by diagnostic codes or laxative use, and patterns of laxative prescriptions overall and across eGFR categories. Multivariable logistic regression models were used to assess the cross-sectional association between eGFR and constipation, adjusting for demographics, vital signs, comorbidities, and medication use. Results: Participants were 49.5 (SD, 10.4) years old, 72% were male, and 12.1% had diabetes. Among the 903 984 person-year observations, 87,861 (9.7%) had constipation. The prevalence of constipation was higher with lower eGFR, with 9.4%, 13.1%, 20.3%, 25.3%, and 45.2% in participants with eGFR ≥60, 45-59, 30-44, 15-29, and <15 ml/min/1.73 m², respectively. Laxative prescription patterns differed by CKD stages, with less use of magnesium salts and greater use of novel agents in more advanced CKD stages. After multivariable adjustment, compared with eGFR ≥60 ml/min/1.73 m², lower eGFR was significantly associated with a higher odds of constipation in a graded manner [adjusted odds ratios (95% CI), 1.07 (1.04-1.11), 1.14 (1.03-1.25), 1.47 (1.20-1.79), and 2.44 (1.84-3.22), respectively]. Conclusion: Constipation was prevalent in patients with CKD. Lower kidney function was independently associated with higher odds of constipation, with the highest odds seen in the most advanced stage of CKD. These findings highlight the real-world burden of constipation across the CKD spectrum and suggest a potential pathophysiological link between constipation and impaired kidney function.