Representatives of the vitamin industry, as well as some other researchers, disputed the findings, criticizing the study for, among other things, including people who were already sick. People tend to take vitamins to stay healthy, they said.

“There’s a large body of data that shows that antioxidant supplementation is beneficial,” said Andrew Shao of the Council for Responsible Nutrition, an industry group. “The message to the average consumer is: Don’t pay attention to this. This doesn’t apply to you. You can go ahead and continue taking your antioxidant supplements in addition to the other things you do in your life to stay healthy.”

But Gluud and his colleagues defended the findings, saying that the study used careful methods developed by the internationally respected Cochrane Collaboration, an independent nonprofit effort to methodically assess medical claims. The analysis included many large studies involving healthy people, and the increased risk was clear after accounting for factors that could confuse the findings, Gluud said.