Protective effects of raw vegetables and fruit against lung cancer among smokers and ex-smokers: a case-control study in the Tokai area of Japan

Abstract

In a hospital-based case control study, the protecting effects of fruit, raw and green vegetables against lung cancer risk among male smokers were studied in 282 cases and the same number of controls. The current smokers showed a 6.61-fold increased risk of lung cancer. The odds ratio (OR) declined markedly with starting age of smoking habit and increased markedly with number of cigarettes smoked per day. The ex-smokers showed a 3.56-fold increased risk of lung cancer. The ORs gradually decreased with years passed since cessation of smoking. In the single factor analysis, significant protective effects of fruit, raw vegetables, green vegetables, lettuce and cabbage against lung cancer were found. The risk for all lung cancer decreased to 0.45 (95% confidence intervals (CI) 0.30-0.67), 0.64 (95% CI 0.43-0.97) and 0.44 (95% CI 0.26-0.73) with increment of intake frequency of fruit, raw and green vegetables respectively. The OR for lung cancer decreased to 0.41 (95% CI 0.24-0.72) and 0.56 (95% CI 0.32-0.99) with increasing intake frequency of fruit and raw vegetables among current smoking males. Lettuce and cabbage showed protective effects against lung cancer, and the OR for risk of lung cancer decreased to one-half among the high intake frequency group. The risk of lung cancer among current smokers declined markedly with increasing intake of lettuce and cabbage. A similar effect was observed among ex-smokers and non-smokers, but there was no statistical significance. In the multivariate analysis, fruit and raw vegetables showed the strongest protective effects against lung cancer among current smokers (P = 0.01). Among ex-smokers, the protective effect of fruit is also statistically significant (P = 0.03). These results suggest that fruit and raw vegetables may play an important role in protecting smokers from lung cancer.