MTHFR and folate deficiency: Moreover, this inhibition of MTHFR enzyme activity might be amplified by folate deficiency.2 As in previous studies, we found that homocysteine negatively correlated with folate concentration in blood (r = −0.33, P value <0.0001) and that homocysteine level was inversely associated with offspring birth weight, even after controlling for folate concentration in blood and other potential confounders.