Cigarette smoking and cardiovascular disease incidence and all-cause mortality: the modifying role of diet quality

Background This study examines the potential long-term interaction between smoking and diet as modifiable risk factors concerning cardiovascular disease (CVD) incidence and all-cause mortality in the Tehran Lipid and Glucose Study framework. Method The study followed 955 smokers from the third and fourth examinations and collected dietary data using a food frequency questionnaire to calculate three different diet quality indices (DQIs): DQI-international, DQI-revised, and Mediterranean-DQI. Current smokers were classified according to smoking intensity and pack-year index. Cox proportional hazards regression models were used to determine the HR (95% CI) of the impact of DQIs, smoking status, and their interaction on CVD incidence and all-cause mortality. Result Over a follow-up period of almost 8 years, 94 cases of CVD (9.8%) and 40 cases of mortality (4.2%) were documented. Although no significant association was found between adherence to the DQI-I and DQI-R indices and the studied outcomes, the study found that lower diet quality based on the Med-DQI was associated with a higher risk of mortality among current smokers (HR: 3.45; 95%CI:1.12, 10.57). Light smokers with higher scores on the DQI-I and DQI-R, compared to heavy smokers with poor diet quality, had a lower risk of CVD incidence (HR: 0.35; 95%CI: 0.35, 0.83) and mortality (HR: 0.20; 95%CI:0.05, 0.77), respectively. Smoking cessation reduced mortality risk (HR: 0.35; 95%CI:0.12, 1.03), and this risk reduction was greater when accompanied by improved diet quality (HR: 0.10; 95%CI:0.02, 0.45). Conclusion Improving diet quality and quitting smoking can lower the risk of CVD and mortality for smokers.