Smoking initiation at young age increases risk of gastric cancer among Korean men

Abstract Objective Early initiation of smoking is associated with adverse health outcomes. This study aimed to investigate the association of various smoking-related factors with the risk of gastric cancer in a population with a high incidence rate of gastric cancer. Method From 2004 to 2013, Korean adults 40–69 years of age were enrolled in the large-scale prospective cohort, the Health Examinees-Gem study. Incident gastric cancer cases were identified until December 31, 2017, through linkage to the Korea Central Cancer Registry. Participants’ information regarding socio-demographics, smoking-related factors, and other lifestyle factors was obtained via self-reported questionnaires. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for gastric cancer risk associated with smoking-related factors such as smoking duration, amount, pack-years, and age of smoking initiation. Results Among 44,207 men included in the final analysis, 565 gastric cancer cases were identified during a mean (± SD) follow-up period of 8.6 (± 2.0) years. Compared to non-smokers, current smokers who smoked more than 35 years (HR 1.44, 95% CI 1.06–1.96) or with ≥ 30 pack-years of smoking (1.40, 1.05–1.87) were positively associated with gastric cancer. These associations were shown to be significant with increasing smoking years ( p trend 0.019) and pack-years (0.016) as well. Compared to non-smokers, current smokers who initiated smoking at a younger age, before or at 20 years, were at a higher risk of gastric cancer (HR 1.46, 95% CI 1.10–1.93). No significant associations were observed among former smokers. When stratified by smoking duration, increased risk of gastric cancer was observed among those who smoked for more than 25 years in the younger smoking initiation age group (≤ 20 years; HR 1.50, 95% CI 1.15–1.94, p for trend = 0.011). In terms of smoking intensity, those who smoked less than 20 cigarettes or 1 pack a day showed an increased risk of gastric cancer in the younger smoking initiation age group that began smoking before or at 20 years of age (1.78, 1.30–2.44, p for trend = 0.006). Conclusion Our findings suggest that earlier initiation of smoking is associated with a greater risk of gastric cancer, regardless of smoking duration. Thus, measures to manage and control onset age of cigarette smoking among teenagers may be considered when taking actions against the health burden of gastric cancer.