Their lung cancer risk went up, not down
Beta-carotene is the antioxidant that makes carrots orange, and researchers expected it to protect smokers' lungs. Two large trials in the 1990s, ATBC and CARET, found the opposite: the supplement groups had more lung cancer, not less. CARET was stopped early because the harm was clear. A compound that looks protective on a lab bench can backfire as a concentrated pill.
