Physicians' Health Study

BACKGROUND:

Thrombosis plays a major role in the late stages of coronary occlusion. Platelet aggregation is a large component in the formation of arterial thrombi. In pharmacologic studies, aspirin has been shown to inhibit platelet aggregation and, therefore, might be expected to prevent coronary occlusion. These effects are apparent in the dose range of l00-l000 mg/day, and may be most evident at l60 milligrams daily. Higher doses seem to be no more effective in either inhibition of platelet agreeability or prolonged bleeding time.

Although an early case-control study by Jick and Miettinen showed a large benefit, most observational studies had shown a cardiovascular benefit of about 20 percent. Conclusive data could only result from a randomized trial with a large sample size.

DESIGN NARRATIVE:

Randomized, double-blind, fixed sample. Participants were randomized into one of four treatment groups: one 325 milligram aspirin tablet every other day, alternating with one 30 milligram capsule of beta-carotene; one aspirin every other day, alternating with one capsule of beta-carotene placebo; one aspirin placebo tablet every other day, alternating with one capsule of beta-carotene; and one aspirin placebo tablet every other day, alternating with one capsule of beta-carotene placebo. Major endpoints for the cardiovascular component of the study were cardiovascular mortality, total mortality, and coronary events.

Male physicians, ages 40 to 84. No history of stroke, myocardial infarction, cancer, or renal disease. No contraindications to aspirin or beta-carotene. No current usage of aspirin or Vitamin A tables greater than once per week.