MTHFR and depressive symptom measurement: The discrepancy in the results of the relationship between erythrocyte folate, serum folate and depression in the present experiment may be due to the fact that erythrocyte and plasma folate concentrations, although highly correlated, are not the same biomarkers of folate status and their relationship is influenced by BMI, methylenetetrahydrofolate reductase (MTHFR) genotype and vitamin B-12 status (24).