Dietary methionine intake and neural tube defects in Mexican-American women.

BACKGROUND: Nutrients other than maternal folic acid are also thought to play a role in preventing neural tube defects (NTDs). Evidence suggests that methionine interacts with folic acid and vitamin B(12) in the methylation of contractile proteins involved in closing the neural folds. The role of dietary intake of methionine in NTD risk has not been specifically studied among Mexican Americans, a population with one of the highest prevalences of NTDs in the United States. METHODS: We conducted a case-control study of 184 Mexican American women with NTD-affected pregnancies (case women) and 225 women with normal offspring (control women) who resided along the Texas-Mexico border. The average daily intakes of methionine were calculated from periconceptional food frequency questionnaire data. Women were categorized according to quartiles of daily methionine intake, based on the control mothers' distribution, and the risk for an NTD-affected pregnancy was calculated using the lowest quartile of intake as the referent. RESULTS: With adjustment for income, body mass index, hyperinsulinemia, and diarrhea, the odds ratios for increasing quartile of methionine intake were: 0.95 (95% confidence interval [CI], 0.48,1.90), 0.92 (95% CI, 0.46,1.84), and 0.66 (95% CI, 0.30,1.45). Some evidence of interaction between dietary methionine and serum vitamin B(12) was noted particularly at higher levels of both components. CONCLUSIONS: This study was limited by a small sample size but examined this association in an exclusively Hispanic population. Results were suggestive of a potential protective effect for NTDs with increasing maternal dietary methionine intake.