Cruciferous vegetable consumption and lung cancer risk: a systematic review.

BACKGROUND Cruciferous vegetables, rich in isothiocyanates, may protect against lung cancer. Glutathione S-transferases are important in metabolizing isothiocyanates; hence, variants in GST genes may modify the association between cruciferous vegetable intake and lung cancer. We carried out a systematic review to characterize the association between cruciferous vegetable intake and lung cancer risk, with an emphasis on the potential interaction between cruciferous vegetables and GSTM1 and GSTT1 gene variants. METHODS A search of the epidemiologic literature through December 2007 was conducted using 15 bibliographic databases without language restrictions. Thirty studies on the association between lung cancer and either total cruciferous vegetable consumption (6 cohort and 12 case-control studies) or specific cruciferous vegetables (1 cohort and 11 case-control studies) were included. RESULTS The risk for lung cancer among those in the highest category of total cruciferous vegetable intake was 22% lower in case-control studies [random-effects pooled odds ratio, 0.78; 95% confidence interval (95% CI), 0.70-0.88] and 17% lower in cohort studies (pooled relative risk, 0.83; 95% CI, 0.62-1.08) compared with those in the lowest category of intake. The strongest inverse association of total cruciferous vegetable intake with lung cancer risk was seen among individuals with GSTM1 and GSTT1 double null genotypes (odds ratio, 0.41; 95% CI, 0.26-0.65; P for interaction = 0.01). CONCLUSIONS Epidemiologic evidence suggests that cruciferous vegetable intake may be weakly and inversely associated with lung cancer risk. Because of a gene-diet interaction, the strongest inverse association was among those with homozygous deletion for GSTM1 and GSTT1.