Interaction between dietary nutrients related to one-carbon metabolism intakes and <i>AHCY</i> rs819173 polymorphism in the risk of gastric cancer: a case–control study in Korea

B vitamin and methionine intake may influence cancer development, but their link to gastric cancer (GC) risk is unclear. Nutrients related to one-carbon metabolism (OCM) have been shown to be associated with <i>S</i>-adenosylhomocysteine hydrolase (AHCY), one of the most crucial enzymes in OCM, which is regulated by the <i>AHCY</i> gene. Thus, we hypothesised that a higher intake of total nutrients related to OCM may reduce the risk of GC, and this preventative effect may interact with the <i>AHCY</i> rs819173 polymorphism. We conducted a case–control study at the National Cancer Center in Korea, involving 371 cases and 738 controls, aiming to determine the interaction between the <i>AHCY</i> rs819173 polymorphism and nutrients related to OCM intakes in GC risk. Dietary vitamin B and methionine intakes were collected using semi-quantitative FFQ (SQFFQ). The OR and 95 % CI were calculated using unconditional logistic regression models. Higher intake of total nutrients related to OCM was found to be inversely associated with GC risk (adjusted OR (aOR) = 0·57, 95 % CI 0·37, 0·86, <i>P</i>_{for trend} = 0·009). No significant association between the <i>AHCY</i> rs819173 polymorphism and GC risk was found. In the dominant model of <i>AHCY</i> rs819173, participants with major homozygous (TT) and higher intake of nutrients related to OCM had a lower GC risk than those with lower intake (aOR = 0·49, 95 % CI 0·30, 0·81, <i>P</i> interaction = 0·015). Higher intakes of total vitamin B and methionine were proposed as potential protective nutrients against GC. Moreover, this association might be influenced by the presence of the <i>AHCY</i> rs819173 polymorphism.