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Rationale for Study


 • Eligibility Criteria

 • Recruitment

 • Intervention

 • Follow-up

 • Data Collection

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Prior to randomization, interested and eligible participants were followed during a 3-month run-in period receiving placebo medication to determine their adherence to taking the study vitamins (as well as to establish their baseline levels of symptoms, signs, and liver function tests). Participants who took at least 50% of their placebo capsules were randomized to either active study vitamins or placebo.

The asbestos pilot study randomized participants to daily doses of either 1) 15 mg beta-carotene and 25,000 IU retinol or 2) placebos. The heavy smoker Pilot study consisted of four intervention arms: 1) 30 mg beta-carotene and 25,000 IU retinol; 2) 30 mg beta-carotene; 3) 25,000 IU retinol; and 4) placebos daily. In the full-scale trial, participants in both exposure populations were assigned to either 1) 30 mg beta-carotene and 25,000 IU retinyl palmitate or 2) placebos daily. Beginning in July 1988, pilot study participants were transitioned to the new protocol. As part of the full-scale trial, pilot study participants were referred to as the Vanguard cohort. The following figure shows the change in intervention arms for pilot study participants on the transition to the full-scale study.

Change in Intervention Arms for the Pilot/Vanguard Cohort

As depicted in the figure, Vanguard participants who were on active arms during the pilot studies had their daily study vitamin dosage changed to 30 mg beta-carotene and 25,000 IU retinyl palmitate; those on placebos continued on placebos. Thus, heavy smoker Pilot participants have a 3:1 allocation to the CARET intervention arms. The form of vitamin A that participants received was changed from retinol to retinyl palmitate to allow the vitamin A and the beta-carotene to be administered in a single capsule.

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