PENN STATE (US)—Health benefits from polyphenol antioxidants—substances found in many fruits and vegetables—may come at a serious cost for some people.

Eating certain polyphenols decreases the amount of iron the body absorbs, which can increase the risk of developing an iron deficiency.

“Polyphenols have been known to have many beneficial effects for human health, such as preventing or delaying certain types of cancer, enhancing bone metabolism, and improving bone mineral density, and decreasing risk of heart disease,” says Okhee Han, assistant professor of nutritional sciences at Penn State.

“But so far, not many people have thought about whether or not polyphenols affect nutrient absorption.”

The researchers, led by Han, studied the effects of eating grape seed extract and epigallocatechin-3-gallate (EGCG) found in green tea.

They used cells from the intestine—where iron absorption takes place—to assess the polyphenols’ effect and found that polyphenols bind to iron in the intestinal cells, forming a non-transportable complex that can’t enter the blood stream.

Instead, it is excreted in the feces when cells are sloughed off and replaced.

Iron is necessary to carry oxygen from the lungs throughout the body and for other cellular functions. People already at risk for iron deficiency increase that risk if they consume high amounts of grape seed extract or EGCG.

“Iron deficiency is the most prevalent nutrient deficiency in the world, especially in developing countries where meats are not plentiful,” says Han.

“People at high risk of developing iron deficiency—such as pregnant women and young children—should be aware of what polyphenols they are consuming.”

Han looked at the heme form of iron found in meats, poultry, and fish. Last year, they performed similar research with non-heme iron found in plants.

Results of the study are published in the Journal of Nutrition.

Both grape seed extract and EGCG are sold in extract form. The results of these studies suggest that consumers should be cautious if using these products.

The research is supported by the National Institutes of Health, National Center for Complementary and Alternative Medicine.

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