Objective: Our purpose was to investigate whether selection of healthy women for postmenopausal estrogen therapy may confound observational studies of estrogen use and cardiovascular disease risk.
Study design: Data were obtained from baseline (1981 to 1984) and follow-up (1990 to 1992) health surveys of two cohorts randomly selected from communities in southeastern New England. At follow-up postmenopausal women > or = 40 years old were categorized as current users (n = 70) or nonusers (n = 772) of noncontraceptive estrogen. Users and nonusers were compared on both prior characteristics from the baseline surveys and current characteristics measured at follow-up by use of analysis of covariance.
Results: Prior levels of total and high-density lipoprotein cholesterol, body mass index, and blood pressure were similar for estrogen users and nonusers. Estrogen users were less likely to have smoked and more likely to have had their cholesterol checked and to exercise regularly. These differences were more pronounced for current characteristics than for baseline characteristics.
Conclusions: Selection of healthy women for treatment may not fully explain the apparent protective effect of estrogen replacement on cardiovascular risk. However, more healthy profiles among estrogen users may inflate the apparent benefit of treatment in observational studies.