Physicians’ Health Study

Study Population

The first phase of the Physicians’ Health Study began in 1982, with funding from the National Cancer Institute and the National Heart, Lung, and Blood Institute. The study had two arms. One group of study participants were used to test whether aspirin prevented cardiovascular events such as a heart attack (myocardial infarction). A second group of participants were used to determine whether beta-carotene was useful in preventing cancer. Physicians aged 40 to 84 years were recruited between 1980 and 1982 as the study participants, and the study was conducted by mail-in survey between 1984 and 1995. A total of 22,071 physicians were eventually randomized into the trial. Principal investigators used physicians as the study population to obtain more accurate medical history and other pertinent health information.

Study Design

PHS-I was constructed to assign study participants to one of four possible treatment scenarios. Study participants received one of the following: two active medications (aspirin and beta-carotene), one active drug and one placebo (active aspirin and a betacarotene placebo, or an aspirin placebo and active beta-carotene), or two placebos (neither pill was an active medication). Using blood samples and followup questionnaires, information was obtained regarding each participant's ability to adhere to the medication regimen, their use of other medications, significant health outcomes, and whether a participant had any illness or disease during the course of the study.

Major Findings

The aspirin arm of the study was stopped in 1988 after a finding that aspirin reduced the risk of myocardial infarction by 44%. This was a highly significant result when compared with the experience of those participants taking the aspirin placebo. Partly as a result of this finding, low-dose (325 mg) aspirin is now recommended as standard care for patients with cardiovascular disease.

The beta-carotene arm of PHS-I concluded in 1995. Although the medical literature had suggested that individuals consuming fruits and vegetables high in beta-carotene had lower rates of cancer, the results of PHS-I failed to demonstrate any positive or negative effect of beta-carotene supplementation on the incidence of cancer.