The Relationship between Body Mass Index and Level of Response to Alcohol Across the Spectrum of Alcohol Use: Total Body Water and Beyond.

Background: A low level of response (LR) to alcohol is a known risk factor for alcohol use disorder (AUD). Although higher total body water (TBW) is associated with lower blood alcohol concentrations and reduced responses following alcohol consumption, the relationship between morphometric measures such as body mass index (BMI) and LR is less clear. This study aimed to examine the relationship between BMI and LR to alcohol, and the contribution of TBW to this relationship.

Methods: Participants (n=1,086) enrolled in the NIAAA Natural History Protocol were assessed for LR to alcohol using the Self-Rating of the Effects of Alcohol (SRE) Questionnaire. BMI was estimated using height and weight, and TBW was estimated from height, weight, age and sex. Participants were categorized based on BMI into 3 groups: normal weight (18.5-25.0 kg/m²; n=430), overweight (25.0-30.0 kg/m²; n=403), and obese (≥30.0 kg/m²; n=253). Associations between BMI group and SRE scores for the most recent three-month period (SRE-Recent), and the effect of TBW, were analyzed using ANOVA. Linear regression analysis was conducted to estimate the proportion of variation in SRE-Recent explained by BMI and TBW.

Results: BMI category was associated with LR, with the normal weight group showing higher responses (lower SRE-Recent scores) to alcohol than the overweight or obese groups. After controlling for TBW, the relationship became non-significant. Linear regression models confirmed these findings.

Conclusions: Higher BMI is associated with lower LR to alcohol. However, TBW seems to account for this relationship, suggesting that concentrations achieved following alcohol consumption may be the primary determinant of BMI-related differences in LR. Future work should replicate these findings and examine these relationships throughout the lifespan and in individuals with AUD.