Smoking, alcohol consumption, and their associations with pulmonary and hepatic function: a cross-sectional study of a health examination cohort

Smoking and heavy drinking often co‑occur, but their joint effects on lung and liver function in the general population are unclear. We examined their separate and combined associations, dose‑response relationships, and additive interactions. Data came from 1,512 adults who had a health examination in 2025. Smoking was measured in pack‑years, alcohol as pure mL/week. Poor lung function was defined as FEV₁/FVC < 0.7 plus FEV₁% predicted < 80%. Abnormal liver tests used ALT, AST and GGT with sex‑specific cut‑offs. We applied regression models, restricted cubic splines, and additive interaction indices (RERI, AP, synergy index). Sensitivity analyses included the lower limit of normal and E‑values. Mean age was 48.5 years; 58.2% were men. Current smokers had lower FEV₁ (‑0.28 L) and 2.41‑times higher odds of abnormal lung function, with a clear dose‑response trend. Heavy drinkers (> 200 mL/week) showed higher ALT (6.4 U/L) and 1.75‑times higher odds of abnormal liver tests. A significant additive interaction was found for liver injury: RERI = 0.58, AP = 0.25, meaning 25% of cases among co‑exposed individuals were attributable to synergy. Associations were stronger in men, older adults, and inactive people. E‑values suggested unmeasured confounding was unlikely to explain the results. Smoking and heavy drinking are independently linked to worse lung and liver function, and together they have a synergistic effect on liver damage. These findings support integrated interventions targeting both behaviours, especially in high‑risk groups.