Influence of hormone replacement therapy on C-reactive protein: population-based data.

Background: Observational data, possibly resulting from confounding due to self-selection, show that use of hormone replacement therapy (HRT) is associated with reduced coronary risk, while randomized trial data do not. One possible explanation for the trial findings is that adverse effects of HRT-- such as an elevation of C-reactive protein (CRP)--might counterbalance other benefits of HRT.

Design: Women aged 40-74 years were identified from a cross-sectional, annual nationally representative study of the English population, the Health Survey for England 1998. Valid data were available from 4,112 of the 4,319 women in this age group. Of these, 710 (17%) were current, 465 (11%) past and 2,937 (71%) never users of HRT.

Methods: To study the association between current and past use of HRT and CRP levels. CRP was expressed as a continuous variable (logged) and in percentiles.

Results: Current, past and never users of HRT did not differ in terms of age, body mass index or smoking status. However, compared with past and never users of HRT, current users tended to take more vigorous physical activity and were more likely to drink more alcohol than is currently recommended. Excluding potentially confounding conditions, median CRP levels were significantly higher in current (2.5 mg/l) and in past (1.9 mg/l) than never HRT users (1.4 mg/l). Controlling for age, smoking and body mass index logged CRP remained significantly raised only among current users.

Conclusions: HRT use was significantly and independently associated with raised CRP levels in an English nationally representative sample. Increases in CRP may represent one plausible mechanism by which HRT may adversely affect risk of coronary heart disease.