Oral estradiol decreases plasma homocysteine, vitamin B6, and albumin in postmenopausal women but does not change the whole-body homocysteine remethylation and transmethylation flux

Estrogens, both endogenous and exogenous, lower the fasting levels of the independent risk factor for cardiovascular disease homocysteine. The mechanism behind this observation remains unclear. In a randomized, placebo-controlled, double-blind study, 25 postmenopausal women with a screening homocysteine concentration above 10 mu mol/liter were included. We investigated the influence on homocysteine levels of a 3-month treatment with a daily oral dose of 4 mg 17 beta-estradiol (ET) or 4 mg ET combined with 10 mg dydrogesterone (EPT); the comparison group received placebo treatment. We performed primed continuous infusions of L-[H-2(3)-methyl-C-13]methionine to assess steady-state flux rates of transmethylation, remethylation, and transsulfuration. Homocysteine concentration relationships with S-adenosylmethionine, S-adenosylhomocysteine, creatinine, albumin, vitamins B-6 and B-12, and folate status were determined as well. The mean change from baseline in homocysteine concentration by both treatments compared with placebo (ET, -13%; EPT, -10%) was accompanied by a decrease in the concentration of vitamin B-6 (ET, -25%; EPT, -38%) and albumin (ET, -7%; EPT, -11%). No significant changes in flux rates were observed. In a multivariate analysis, changes in homocysteine concentration were related to changes in albumin concentration. No relation to other variables was observed. We conclude that the ET- and EPT-induced homocysteine changes in this study were not accompanied by a significant change in methionine-homocysteine flux rates and hypothesize that an estrogen-induced lowering of homocysteine levels is primarily part of a change in albumin metabolism.