Combined Effects of PFAS on Constipation Response Scores and Bowel Movement Frequency

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants with growing evidence of systemic health effects, but their potential influence on gastrointestinal function remains poorly understood. This study evaluated associations between serum PFAS mixtures and bowel health indicators, including self-reported constipation and bowel movement frequency, among 116 U.S. adults aged ≥20 years from the 2009–2010 National Health and Nutrition Examination Survey. Six PFASs were examined: PFOS, PFOA, PFHS, PFNA, PFDE, and PFUA. Constipation was assessed using the NHANES Bowel Health Questionnaire item coded from 1 = Always to 5 = Never, so that higher values represented less frequent self-reported constipation, and bowel movement frequency was recorded as movements per week. Bayesian kernel machine regression (BKMR) estimated joint and nonlinear mixture effects, and survey-weighted regression models examined individual PFAS, each adjusted for age, sex, body mass index, education, and income. Higher combined PFAS exposure was associated with higher constipation response scores across the mid-range of exposure, indicating less frequent self-reported constipation, with PFOA identified as the primary contributor through a nonlinear, inverse U-shaped exposure–response pattern. In survey-weighted models, PFOA and PFUA were associated with less frequent self-reported constipation, whereas PFNA was associated with more frequent constipation. Associations with bowel movement frequency were weak and inconsistent; only PFOS reached significance in regression, and this association would not survive correction for multiple comparisons, so these data provide little evidence of a robust association between PFAS and bowel movement frequency. Overall, higher PFAS exposure was associated with less frequent self-reported constipation, particularly for PFOA, whereas evidence for an association with bowel movement frequency was limited.