The vitamin that raised the cancer risk it was sold to lower

Beta-carotene is the orange pigment that gives carrots their color, and by the late 1980s it looked like one of the great free lunches of preventive medicine. It's an antioxidant, it's abundant in vegetables people are already told to eat more of, and observational studies kept finding that people who ate more beta-carotene-rich food had lower cancer rates. Supplement companies packaged it into pills and sold it as insurance.

Then someone actually tested it. Large randomized trials gave high daily doses of beta-carotene to smokers and former smokers, the group with the most to gain from a cancer shield. The supplement didn't lower lung cancer risk. In several of these trials it appears to have raised it.

A 2013 meta-analysis of randomized controlled trials found that beta-carotene supplementation at high doses — above roughly 9.6 milligrams a day, well beyond what you'd get from food — was associated with a 6% increase in all-cause mortality. Lower doses showed no clear effect either way. The vegetables were never the problem; something about concentrating the compound into a pill, stripped of the hundreds of other things a carrot also contains, changed the story entirely.

Antioxidants aren't fake. But a molecule correlated with health inside a carrot is not the same molecule tested inside a capsule — and only one of those has actually been checked.