Polyphenols’ Antioxidant Glitter is Not Gold for All

June 29, 2010

Polyphenols’ antioxidant health benefits may come at a cost to some people. Penn State researchers found that eating certain polyphenols decreases the amount of iron the body absorbs, which can increase a person’s risk for developing iron deficiency. The researchers, led by Dr. Okhee Han, assistant professor of nutritional sciences, studied the effects of eating several polyphenols: grape seed extract and EGCG (epigallocatechin-3-gallate), which is found in green tea.

“Polyphenols have been known to have many beneficial effects for human health, such as preventing or delaying certain types of cancer, enhancing bone metabolism, decreasing risk of heart disease, and improving bone mineral density,” says Han. “But so far, not many people have thought about whether or not polyphenols affect nutrient absorption.”

The researchers used cells derived from the intestine—where iron absorption takes place—to assess the polyphenols’ impact. They found that polyphenols bind to iron molecules in the intestinal cell, forming an insoluble complex. When this happens, the iron cannot make its way into the blood stream, where it would normally go to carry out its role in numerous functions inside the body. Instead, it is excreted through the digestive tract along with other insoluble compounds (e.g., fiber).

Iron helps carry oxygen from the lungs throughout the body, in addition to being used in several cellular functions. If a person is already at risk for iron deficiency, this risk could increase if they consume high amounts of grape seed extract and 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.”

Although iron deficiency is the most prevalent form of iron malnutrition, there is also a hereditary disease, hemochromatosis, that causes the opposite problem—iron overload. For people with this disease, consuming polyphenols may be another outlet for keeping iron at safe levels.

In this study, the results of which were published in the Journal of Nutrition, Han and her colleagues looked at one of iron’s two forms, heme, which is commonly found in meats, poultry, and fish. Last year, they performed similar research with iron’s other form, non-heme, which is commonly found in plants. The results of their previous study were similar to the most recent study: eating polyphenols decreased iron absorption.

Both grape seed extract and EGCG are available on the market in extract form. The results of these studies indicate that consumers should be cautious if using these products.

Han and her colleagues recently received a grant from the National Center for Complementary and Alternative Medicine (part of the National Institutes of Health) to expand upon their research. They will be conducting a study with animals, and they eventually hope to perform research in humans. Other authors on the paper include Qianyi Ma, graduate student in the Department of Nutritional Sciences, and Eun-Young Kim, research assistant, Department of Nutritional Sciences.

This study was funded by Penn State’s College of Health and Human Development.

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Editors: Okhee Han can be reached at ouh1@psu.edu. For additional information, please contact the College of Health and Human Development Office of College Relations at 814-865-3831 or healthhd@psu.edu.