Association between caffeine intake and constipation in a U.S. population aged 20 to 65 years: Results from NHANES 2007 to 2010

Caffeine's relationship with constipation is unclear. Some studies suggest caffeine may promote bowel movement, while excessive intake could worsen symptoms. This cross-sectional study aimed to evaluate the association between caffeine intake and constipation among U.S. adults aged 20 to 65 years using data from the 2007 to 2010 National Health and Nutrition Examination Survey. Caffeine intake was categorized into quartiles based on 24-hour dietary recall data, and constipation was defined using stool form, bowel movement frequency, and self-reported symptoms. Weighted multivariable logistic regression, restricted cubic spline modeling, and subgroup and interaction analyses were conducted to assess associations and test the robustness of results. Compared with participants in the lowest quartile of caffeine intake (≤35.5 mg/d), those in the third quartile (109.1-228.5 mg/d) had the lowest odds of constipation (odds ratio [OR]: 0.60; 95% confidence interval: 0.44-0.82; P =.004). When modeled on a log2 scale, each doubling of caffeine intake was associated with a modest reduction in the odds of constipation (OR: 0.95, 95% confidence interval: 0.91-0.99; P =.019). Restricted cubic spline analyses supported a nonlinear association (P for nonlinear <.01); the curve crossed the null (OR = 1) at approximately 580 mg/d, with no further benefit observed at higher intakes. No significant effect modification was detected across prespecified subgroups. Moderate caffeine consumption was associated with a lower likelihood of constipation, whereas higher caffeine intake did not confer additional benefits. These findings suggest a potential threshold effect of caffeine on bowel function, beyond which further intake may not provide added advantage. Further longitudinal and mechanistic studies are warranted to confirm these associations and clarify the biological pathways linking caffeine consumption to bowel motility.