Association between waterpipe smoking and lung cancer: a multicentre case–control study in Iran

Objectives: This study investigated the association between lung cancer and waterpipe smoking, which is an emerging global public health concern. Study design: Multicentre case-control study. Methods: This study included 627 cases and 3477 controls from the Iranian Study of Opium and Cancer (IROPICAN) study, which was conducted between 2017 and 2020. One frequency-matched control for each lung cancer patient was selected by age, gender and residential place; however, this study used controls of four cancer types in the analyses. The multivariable logistic regression model estimated the odds ratio (OR) and 95% confidence intervals (CIs). Additional analyses were performed among 181 lung cancer cases and 2141 controls who were not cigarette smokers or opium or nass/pipe users. Results: The odds of lung cancer were higher among waterpipe smokers than never-smokers (OR = 1.3, 95% CI: 1.0–1.7). Results showed a higher OR of lung cancer for those who smoked the waterpipe daily (OR = 2.1, 95% CI: 1.4–3.0), smoked more than two heads per day (OR = 2.7, 95% CI: 1.8–4.0), had smoked for >20 years (OR = 1.9, 95% CI: 1.3–2.7), smoked more than 20 head-years (OR = 2.8, 95% CI: 1.9–4.1) and initiated smoking before the age of 30 years (OR = 1.7, 95% CI: 1.1–2.5). The association was only statistically significant for squamous cell carcinomas (OR = 1.8, 95% CI 1.2–2.7). Furthermore, this study observed a higher OR of lung cancer among exclusive waterpipe smokers (OR = 2.3, 95% CI: 1.6, 3.5). Conclusions: Waterpipe smoking was associated with an increased risk of lung cancer. The association was stronger with higher frequency, duration and intensity of exposure to waterpipe smoking. The association increases in exclusive waterpipe smokers, which is likely due to controlling for residual confounding by cigarette smoking and opium consumption, and higher exposure levels in this subpopulation.