We aimed to evaluate the hypothesis that the presence of an interaction between smoking and being overweight increases the risks of lifestyle-related diseases (hypertension, diabetes mellitus, dyslipidemia, and cardiovascular disease) in outpatients with mood disorders.

In this cross-sectional survey, using data from 213 outpatients with mood disorders (95 men, 118 women), we calculated the adjusted odds ratios ( ORs ) with 95% confidence intervals (CIs) for each of hypertension, diabetes, dyslipedemia, and cardiovascular disease, using a binary logistic regression model; we then calculated the adjusted OR values for smokers and non-smokers with body mass indexes (BMIs) of 2. Next, we examined the data for the presence of an interaction between smoking and being overweight, using three measures of additive interaction: relative excess risk due to the interaction (RERI), attributable proportion due to the interaction (AP), and the synergy index ( S ).

Smokers with BMI 2 had a significantly lower risk of hypertension (OR 0.27, 95% CI 0.09–0.81) than non-smokers with BMI 2 (reference group). Compared with the reference group, overweight non-smokers had a significantly higher risk (2.82, 1.34–6.19) of hypertension, and overweight smokers had a higher risk (4.43, 1.28–15.26) of hypertension and very high risks of diabetes (8.24, 2.47–27.42) and cardiovascular disease (13.12, 1.95–88.41). The highest RERI was derived from the relation with cardiovascular disease. The highest AP and S were derived from the relation with type 2 diabetes. There was no interaction of smoking and being overweight with dyslipidemia.

The presence of an interaction between smoking and being overweight exacerbates the risks of hypertension, diabetes, and cardiovascular disease in outpatients with mood disorders.