Association between oral health and bowel habits: a cross-sectional study

Background Oral diseases affect approximately 3.5 billion people worldwide, disproportionately burdening populations in developing countries. Chronic diarrhea and constipation, as common intestinal disorders, may interact bidirectionally with oral health, though their population-level associations remain unexamined. Methods We analyzed data from the National Health and Nutrition Examination Surveys (NHANES) 2005–2008, selecting participants based on inclusion criteria. Chronic diarrhea and constipation were defined based on the bowel health questionnaire. Oral health indicators (teeth condition and oral pain frequency) were derived from the oral health questionnaire. Covariates selected by Lasso regression were analyzed through adjusted logistic regression to examine associations between bowel habits and oral health. Restricted cubic splines (RCS), subgroup stratification, and sensitivity analyses were also used. Results A total of 7512 participants aged ≥ 20 with complete information were included. Multivariable logistic regression revealed a significant association between chronic constipation and poor teeth condition (OR:1.45, 95% CI: 1.05–2.01, P  = 0.029). A U-shaped dose-response relationship was observed between stool frequency and poor teeth condition (nonlinear P -value = 0.002) using RCS analysis, with both abnormally low and high bowel frequencies correlating with increased oral health risks. No significant association was identified between oral pain frequency and abnormal bowel habits after full covariate adjustment. Stratified analyses indicated that daily dietary fiber intake ≥ 25 g was associated with reduced risks of poor teeth condition (chronic diarrhea OR: 0.40, 95% CI: 0.12–0.98; chronic constipation OR: 0.44, 95% CI: 0.13–1.09), whereas higher income (PIR > 3.5) correlated with elevated risks (chronic diarrhea OR: 2.38, 95% CI: 1.35–3.98; chronic constipation OR: 2.18, 95% CI: 1.22–3.70). Sensitivity analyses supported the stability of associations between abnormal bowel habits and poor teeth condition. Conclusions Both chronic constipation and diarrhea were associated with higher risk of poor teeth condition. In the general population and subgroup analyses, individuals with stool frequency around 8–10 times per week demonstrated the lowest risk of poor teeth condition. Stratified analysis indicates that dietary fiber intake and PIR might modify the observed relationship between abnormal bowel habits and teeth condition.