Sequentially combined estradiol valerate plus levonorgestrel therapy decreases 18:1 trans-fatty acid content of plasma lipids in healthy postmenopausal women

Trans-fatty acids (TFA) have been classified as atherogenic dietary constituents but the effect of hormone replacement therapy (HRT) on their concentrations is not known. We used a washout protocol to study the effect of long-term estrogen and combined estrogen-progestin HRT on plasma elaidate (18:1t), which is the trans isomer of oleate and the major TFA in the diet. The study group comprised 15 women receiving estradiol valerate HRT and 15 women receiving combined HRT with estradiol valerate and levonorgestrel. The concentrations of elaidate in plasma phospholipids, cholesteryl esters and triglycerides were determined by gas chromatography. At baseline, the total plasma elaidate concentration was lower in the combined HRT group than in the estradiol valerate HRT group (p < 0.01). In the combined HRT group, the concentration of elaidate increased significantly after withdrawal of HRT (p < 0.001) and decreased again to the baseline level after restart of therapy (p < 0.001). These changes were due to decreases in the concentrations of phospholipids; and triglycerides; in phospholipids there was also a proportional decrease of elaidate. There were no changes in elaidate in women receiving estradiol valerate alone. Our results suggest that long-term combined HRT treatment decreases plasma TFA, which is not achieved by estrogen alone.