C677T methylenetetrahydrofolate reductase and plasma homocysteine levels among Thai vegans and omnivores.

Hyperhomocysteinemia among vegetarians and vegans is caused mostly by vitamin B12 deficiency. A C-to-T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene results in a thermolabile MTHFR, which may affect homocysteine (Hcy) levels. The importance of this gene mutation among populations depends on the T allele frequency. Blood Hcy, vitamin B12, folate, vitamin B6, and MTHFR C677T mutation status were determined in 109 vegans and 86 omnivores aged 30 - 50 years. The vegans had significantly higher Hcy levels than the omnivores, geometric means (95 % CI) 19.2 (17.0 - 21.7) µmol/L vs. 8.53 (8.12 - 8.95) µmol/L, p < 0.001. A C-to-T mutation in the vegans increased plasma Hcy, albeit insignificantly; geometric means 18.2 µmol/L, 20.4 µmol/L, and 30.0 µmol/L respectively in CC, CT, and TT MTHFR genotypes. There was also a significant decrease in serum folate; geometric means 12.1 ng/mL, 9.33 ng/mL, and 7.20 ng/mL respectively, in the CC, CT, and TT mutants, p = 0.006, and particularly, in the TT mutant compared with the CC wild type, 7.20 ng/mL vs. 12.1 ng/mL, p = 0.023. These findings were not seen in the omnivores. It was concluded that hyperhomocysteinemia is prevalent among Thai vegans due to vitamin B12 deficiency. C-to-T MTHFR mutation contributes only modestly to the hyperhomocysteinemia.