Body mass index and the risk of lung cancer incidence in smokers: a prospective cohort study

Abstract

To investigate the effect of baseline body mass index (BMI) on the risk of lung cancer incidence in male smokers. All the male employees and retirees of the Kailuan Group were recruited in the Chinese Kailuan Male Cohort Study, and they had been experienced routine physical examinations every two years since May, 2006. Up to 31st December 2011, a total of 3 rounds physical examinations had been completed. A total of 42 718 male smokers candidates from the Chinese Kailuan Male Cohort Study were enrolled in the present study. The date of entering this study was defined as that of taking first check-up, and the date of end-of-observation was defined as that of cancer diagnosis, death or end of follow-up (31 December 2011). Information on demographics, lifestyle such as smoking, alcohol consumption, anthropometries such as height and weight, as well as the information of newly-diagnosed cancer cases, were collected at the baseline investigation. Multivariable Cox proportional hazards regression models were used to investigate the association between levels of the baseline BMI and risk of lung cancer. Of the 42 718 male smokers, there were 181 998.09 person-years of follow-up, taking 4.26 years of average follow-up period. During follow-up, 234 new lung cancer cases were identified among the 42 718 male smokers and the crude incidence density was 128.57/100 000. After the factors adjustment for age, education level, alcohol consumption, physical activity, work environment and cumulative smoking levels (pack-years), compared with subjects of normal BMI group, hazard ratio and 95% confidence intervals of lung cancer for subjects of underweight, overweight, and obesity were 1.63 (0.79-3.37), 0.79 (0.57-1.09) and 0.50 (0.27-0.91), respectively. After the facotors adjustment for age, education level, alcohol consumption, physical activity, work environment and cumulative smoking levels (pack-years), compared with subjects of normal BMI, hazard ratio and 95% confidence intervals of lung cancer for subjects of obesity among subjects who aged 50 years or above, smoked more than 20 pack-years, and exercised less than 4 times per week were 0.33 (0.15-0.71), 0.27 (0.10-0.75), and 0.44 (0.20-0.96), respectively. Obesity subjects who worked above the well had decreased risk of lung cancer (HR=0.38, 95% CI: 0.15-0.96) compared with normal BMI ones who worked above the well. BMI was negatively correlated with the risk of lung cancer in male smokers. As for male smokers, one of the most effective approaches to prevent and control the lung cancer has been shown to quit smoking and keep fit.