Objective  To investigate the correlation between tea and dairy products intake with primary lung cancer among people neither smoking nor drinking alcohol and to provide references for prevention and control of primary lung cancer.

  Methods  We conducted a case-control study among people neither smoking nor drinking alcohol recruited at the First Affiliated Hospital Fujian Medical University, Affiliated Union Hospital of Fujian Medical University and Fuzhou General Hospital of Nanjing Military Region from January 2006 to July 2015. The cases were 564 primary lung cancer patients pathologically confirmed at the three hospitals and the controls were 564 gender- and age-matched healthy people who visited some inpatients in the three hospitals. Face-to-face interviews were carried out among all the participants with a self-designed questionnaire.

  Results  The results of unconditional logistic regression analysis revealed that after adjusting for confounding factors such as gender, age, nationality, education, body mass index, passive smoking at home, passive smoking in workplace, lung disease history, family history of cancer, and kitchen fume exposure, the participants drinking tea ≥ one cup/per week continuously at least for a half year had a significantly decreased risk of lung cancer (odds ratio OR = 0.457, 95% confidence interval 95% CI: 0.341 – 0.613; for drinking black tea: OR = 0.351, 95% CI: 0.187 – 0.657; for drinking green tea: OR = 0.493, 95% CI: 0.326 – 0.745; for drinking scented tea: OR = 0.207, 95% CI: 0.090 – 0.474) compared with those not drinking tea; moreover, the duration of tea consumption (years) and the amount of tea consumed per week, the concentration of tea consumed, and the amount of tea consumption per month were all correlated significantly with the risk of primary lung cancer in a dose-response manner (all P < 0.001). The results of logistic regression also demonstrated that the participants consuming dairy products had a significantly decreased risk of lung cancer (OR = 0.503, 95% CI: 0.387 – 0.653) in comparison to those not consuming dairy products and the frequency and amount of dairy consumption were correlated with the decreased risk in a dose-response manner (both P < 0.001). A multiplicative interactive effect of tea drinking and dairy product consumption on incidence of primary lung cancer was observed (P_interaction < 0.001); the participants drinking tea and consuming dairy products had a significantly decreased primary cancer risk (OR_interaction = 0.195, 95% CI: 0.129 – 0.294) compared with those not drinking tea and not consuming dairy products.

  Conclusion  Drinking tea and consuming dairy products are protective factors against primary lung cancer and interactive effect of tea drinking and dairy product consumption could decrease the risk of primary lung cancer among people neither smoking nor drinking alcohol.