Association between folate intake, serum folate levels and the risk of lung cancer： a systematic review and meta-analysis

Background Folate plays a critical role in nucleotide synthesis and DNA methylation, and was considered to be associated with anti-carcinogenesis. Results from studies that concern the relationship between the folate intake or serum folate levels and lung cancer risk showed no consistency, which requires our further comprehensive meta- analysis. Methods Systematic literature search was conducted to identify the relevant studies （published prior to February 2013） according to standard protocol. Estimated effects were calculated under both random-effects and fixed-effects models. Heterogeneity between studies and publication bias were also evaluated. Results A total of 4390 cases and 6138 controls from 6 case-control studies revealed a significant overall inverse association between folate intake and lung cancer risk （OR = 0.74, 95% CI = 0.65-0.84, P〈 0.001）. Summary of 1438 cases and 2582 controls from 4 case-control studies and 44 cases out of a cohort of 1988 participants suggested a marginal association without significance （OR = 0.78, 95% CI = 0.60-1.02, P = 0.075） between high serum folate levels and less lung cancer susceptibility; however, subgroup analysis about population-based case-control studies showed that high serum folate levels significantly associated with the reduced lung cancer risk （OR = 0.76, 95% CI = 0.58-1.00, P = 0.048）. Conclusion Higher folate intake can be a protective factor against lung cancer risk, and higher serum folate level is probably associated with reduced lung cancer risk in marginal manner, though more studies are warranted to confirm these associations.