Folate, homocysteine levels, methylenetetrahydrofolate reductase (MTHFR) 677 C → T variant, and the risk of myocardial infarction in young women: Effect of female hormones on homocysteine levels

In young women data are limited about the association between myocardial infarction (MI) and hyperhomocysteinemia, low folate or methylenetetrahydrofolate reductase (MTHFR) genotypes. The effect of oral contraceptive (OC) use on plasma homocysteine levels is not clear. We assessed the association between hyperhomocysteinemia, low folate, MTHFR 677TT mutation and risk of MI, and we investigated the effect of OC use on homocysteine levels in controls. In 181 patients with a first MI and 601 controls 18-49 years of age from a population-based case-control study, non-fasting blood samples were available. The homozygote mutant allele (TT) was detected in 12% of the patients and in 10% of controls. The odds ratio (OR) for MI in TT patients compared with the wild-type (CC) controls was 1.3 [95% confidence interval (CI) 0.8, 2.3]. For all MTHFR genotypes combined, the OR for MI in the lowest quartile of folate (<5.4 nmol L^-1) compared with the highest quartile (>10.4 nmol L^-1) was 3.0 (95% CI 1.7, 5.1). A 2-fold increased risk of MI was found in women with the TT genotype who had folate levels below the median of 7.4 nmol L^-1 compared with CC genotype and folate levels above the median (OR =2.0; 95% CI 1.0, 3.7). Mean homocysteine levels were 12.2 μmol L^-1 in OC users and 12.3 μmol L^-1 in non-users. Only at the 97.5 percentile (cut-off 21.0 μmol L^-1) was the adjusted OR for higher vs. lower homocysteine levels increased by 2.8-fold (95% CI 1.2, 6.8). Low folate is a risk factor for MI, particularly in women with the MTHFR 677TT genotype. Homocysteine levels were not influenced by OC use.