Nonlinear Relationship Between Body Mass Index and Esophageal Acid Exposure in the Extraesophageal Manifestations of Reflux

BACKGROUND & AIMS: Obesity is believed to be an important etiologic factor in gastroesophageal reflux disease. However, it is not clear how obesity might affect esophageal acid exposure in patients with extraesophageal manifestations of reflux. METHODS: We conducted a cross-sectional study of 223 patients with extraesophageal symptoms suspected of being related to reflux. Participants underwent endoscopy and 48-hour wireless pH testing. The percentage of time at a pH of less than 4 (total, upright, and supine) was measured for each patient, and data were compared with corresponding body mass index (BMI), as continuous and categoric variables (normal, 18.5 to <25; overweight, 25 to <30; and obese, >30). Multivariable linear regression was used to identify variables associated with percentage of total time at a pH less than 4. The primary predictor of interest was BMI; age, sex, esophagitis, and hiatal hernia status were considered potential confounders or precision variables. RESULTS: Esophageal acid exposure was associated significantly (P < .001) with BMI. The percentage of time at a pH less than 4 and total symptomatic reflux events increased significantly (P = .005) with increasing BMI. The relationship between percentage of time at a pH less than 4 and BMI was nonlinear and S-shaped. With BMI ranges, the percentage of time at a pH less than 4 increased by 0.23% (normal BMI), 0.75% (overweight), and 0.07% (obese) for every 1-kg/m(2) increase in BMI (P < .001). CONCLUSIONS: Increases in esophageal acid exposure are greatest among overweight patients and plateau in obese patients. The findings have implications for benefit of weight loss in patients with suspected extraesophageal manifestations of gastroesophageal reflux disease.