Body mass index, physical activity and dental caries: cross-sectional HUNT4 oral health study

Studies on the association between body mass index (BMI) and dental caries among adults are limited. Moreover, individuals with a high BMI may be either physically active or inactive, but the impact of these combinations on dental caries remains unexplored. In this study, we aimed to investigate the associations between BMI, its combination with physical activity (PA), and dental caries in the adult population. We conducted a cross-sectional analysis using data from Norwegian HUNT4 Oral Health Survey (2017-2019). BMI was categorized as < 25.0 (normal), 25.0-29.9 (overweight), or ≥ 30.0 kg/m² (obese). The combination of BMI and PA was classified into 4 groups: (1) normal weight and active; (2) normal weight and inactive; (3) overweight-obese and active; and (4) overweight-obese and inactive. Main outcomes included the total number of decayed, missing, and filled teeth (D₃MFT) and decayed teeth (D₃T), while missing and sound teeth were secondary outcomes. Ratios of means (RM) with 95% confidence intervals (CI) were calculated using negative binomial regression. Effect modification by age (< 65 vs. ≥ 65 years) was assessed via the likelihood ratio test. We included 4752 individuals with a mean age of 51.9 years (SD 15.9). Compared to individuals with BMI < 25 kg/m², those with BMI ≥ 30.0 kg/m² was associated with an increased mean number of D₃MFT (adjusted RM: 1.10, 95% CI 1.07-1.13), D₃T (1.19, 95% CI 1.07-1.32), and missing teeth (1.11, 95% CI 1.00-1.22), but inversely with sound teeth (0.96, 95% CI 0.92-0.99). No combined effect of BMI and PA was observed. The association between BMI and dental caries was modified by age, with an association observed in individuals under 65 years (P_{likelihood ratio test} < 0.001). We observed that a higher BMI was associated with a higher dental caries experience and missing teeth. However, there was no evidence of a combined effect between BMI and PA on dental caries.