Americans today consume more nutrients than ever. In addition to enriched foods and energy drinks, half the country regularly takes a vitamin or mineral supplement. People with health problems may need additional nutrients. But for most Americans, researchers don’t know for sure whether extra doses really help — and caution that in some cases, they might hurt.

“We don’t have long-term clinical trial data on the efficacy or safety of supplements,” said Regan Bailey, a nutritional epidemiologist and associate professor at Purdue University. So “consumers need to be aware of how much they’re getting.”

Below, compare the dosages for some of the most common supplements to the amount of nutrients available in everyday foods. And for more, watch our documentary, Supplements and Safety, beginning Tues. Jan. 19.