Body mass index and lung cancer: a case-control study of subjects participating in a mass-screening program.

STUDY OBJECTIVES An inverse relationship between body mass index (BMI) and the risk of lung cancer, suggesting that leanness is a risk factor for lung cancer, has been reported in previous studies. In order to evaluate the risk of lung cancer associated with lower levels of BMI in preclinical patients, we conducted a case-control study based on the results of community mass screening. DESIGN The relationship between BMI (at the time of diagnosis, and at 1 to 5 years prior to diagnosis) and lung cancer was investigated in a case-control study of 363 lung cancer cases and 1,089 control subjects conducted between April 1993 and March 2003. Control subjects were selected from mass-screening subjects with no abnormalities on chest radiography and routine laboratory tests. RESULTS In men, an inverse association between BMI and lung cancer was observed after adjustment for age and smoking (BMI < 20.8; range of the referent group, > or = 22.9 to < 25.0; odds ratio, 1.9; p = 0.0025; 95% confidence interval, 1.3 to 2.9). In women, however, no association was found between BMI and lung cancer (BMI < 20.8, p = 0.3868; and BMI </= 25.0, p = 0.4603, respectively). In addition, a negative association between BMI at 4 to 5 years prior to diagnosis and lung cancer was not observed in either gender (men, p = 0.2937 to 0.5783; women, p = 0.2042 to 0.9326). CONCLUSIONS Our present study indicated the possibility that the previously reported association between leanness and the risk of lung cancer in women was not correct, and this apparent association might be influenced by other factors such as smoking and smoking-related respiratory diseases. A larger-scale cohort study combined with mass-screening project will confirm our results.