Effects of hormone replacement therapies on fibrinogen and plasma viscosity in postmenopausal women.

In women, cardiovascular morbidity and mortality sharply increase after the onset of menopause. There is substantial evidence that hormone replacement therapy (HRT) may decrease the risk of coronary heart disease (CHD); however, the mechanisms of this preventive effect are unclear. We investigated the association between HRT and plasma viscosity as well as fibrinogen levels in postmenopausal women of a population-based sample (n=300, age 52-65 years). A total of 94 women used HRT; of these, 50 took oestrogen monotherapy and 44 used oestrogen-progesterone combinations. HRT was associated with significantly lower fibrinogen concentrations (2.32 v 2.68 g/l, P<0.001) and decreased plasma viscosity (1.147 v 1.176 mPa/s, P=0.01). Multivariate analyses controlling simultaneously for the effects of age, smoking, body mass index, and use of diuretics confirmed decreased fibrinogen and plasma viscosity values in women using HRT. A trend towards lower plasma viscosity (1.139 v 1.160 mPa/s) and plasma fibrinogen (2.28 v 2.44 g/l) was observed in women on oestrogen-progesterone combinations as compared with oestrogen monotherapy users: however, after controlling for the above-mentioned variables these differences were not statistically significant. This study demonstrates decreased plasma viscosity in women on HRT. Improved rheology offers a mechanism by which HRT lowers the risk of CHD in postmenopausal women.