The Bayes factors indicated no evidence for any associations between lung cancer and the main effects of betaine, choline or riboflavin or the SNPs involved in the interactions, but as the intake of betaine and allele dose of rs2658161 (MTRR) and rs16948305 (TYMS) increased, our model indicated a reduction in lung cancer risk for former smokers. This evidence concerns the gene TYMS and lung cancer.