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Does vitamin A supplementation prevent cancer? Observational studies had shown that people eating more fruits and vegetables, which are rich in beta carotene (that the body can convert into retinol, or vitamin A), had lower rates of lung cancer. The Beta-Carotene and Retinol Efficacy Trial (CARET) tested the combination of beta-carotene and vitamin A supplements in men and women at high risk of developing lung cancer. The CARET intervention was stopped 21 months early because of clear evidence of no benefit and substantial evidence of possible harm.

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