Could extracts of green tea and grape seeds slash iron?
According to the latest research, that’s just what these two polyphenols could do.
In laboratory tests done at Penn State University, grape seed extract and green tea extract (EGCG) reduced iron absorption.
While the tests were not done on humans or animals, people taking these pills should be aware of the potential impact on nutrient absorption.
The results were published in the Journal of Nutrition. See the links below to the full text of the articles available on the Journal’s website.
Learn more about how pills can reduce nutrients with the Pill Advised application.
Read the full release from Penn State University:
Polyphenol antioxidants inhibit iron absorption
23-Aug-2010
University Park, Pa. — Health benefits from polyphenol antioxidants — substances found in many fruits and vegetables — may come at a cost to some people. Penn State nutritional scientists found that eating certain polyphenols decreased 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," said Okhee Han, assistant professor of nutritional sciences. "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. This iron-polyphenol complex cannot 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," said 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 and her colleagues 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. They published the results of their study on grape seed extract and EGCG in the Journal of Nutrition, showing that eating polyphenols decreased iron absorption.
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.
Han and her colleagues recently received a grant from the National Institutes of Health, National Center for Complementary and Alternative Medicine to expand this research. They will conduct animal studies and eventually hope to do human studies as well. Other authors on the paper include Qianyi Ma, graduate student in nutritional sciences, and Eun-Young Kim, research assistant in nutritional sciences.
Source: Penn State University
References:
J Nutr. 2010 Jun;140(6):1117-21. Epub 2010 Apr 7.
Bioactive dietary polyphenols decrease heme iron absorption by decreasing basolateral iron release in human intestinal Caco-2 cells.
Ma Q, Kim EY, Han O.
Department of Nutritional Sciences, Pennsylvania State University, University Park, PA 16802, USA.
Because dietary polyphenolic compounds have a wide range of effects in vivo and vitro, including chelation of metals such as iron, it is prudent to test whether the regular consumption of dietary bioactive polyphenols impair the utilization of dietary iron. Because our previous study showed the inhibitory effect of (-) -epigallocatechin-3-gallate (EGCG) and grape seed extract (GSE) on nonheme iron absorption, we investigated whether EGCG and GSE also affect iron absorption from heme. The fully differentiated intestinal Caco-2 cells grown on microporous membrane inserts were incubated with heme (55)Fe in uptake buffer containing EGCG or GSE in the apical compartment for 7 h. Both EGCG and GSE decreased (P < 0.05) transepithelial transport of heme-derived iron. However, apical heme iron uptake was increased (P < 0.05) by GSE. Despite the increased cellular levels of heme (55)Fe, the transfer of iron across the intestinal basolateral membrane was extremely low, indicating that basolateral export was impaired by GSE. In contrast, EGCG moderately decreased the cellular assimilation of heme (55)Fe, but the basolateral iron transfer was extremely low, suggesting that the basolateral efflux of heme iron was also inhibited by EGCG. Expression of heme oxygenase, ferroportin, and hephaestin protein was not changed by EGCG and GSE. The apical uptake of heme iron was temperature dependent and saturable in fully differentiated Caco-2 cells. Our data show that bioactive dietary polyphenols inhibit heme iron absorption mainly by reducing basolateral iron exit rather than decreasing apical heme iron uptake in intestinal cells.
Full Article at the Journal of Nutrition: http://jn.nutrition.org/cgi/content/full/140/6/1117
J Nutr. 2008 Sep;138(9):1647-51.
Bioactive dietary polyphenolic compounds reduce nonheme iron transport across human intestinal cell monolayers.
Kim EY, Ham SK, Shigenaga MK, Han O.
Department of Nutritional Sciences, Pennsylvania State University, University Park, PA 16802, USA.
There is persuasive epidemiological evidence that regular intake of dietary bioactive polyphenolic compounds promotes human health. Because dietary polyphenolic compounds have a wide range of effects in vivo and vitro, including chelation of metals such as iron, it is prudent to test whether the regular consumption of bioactive polyphenolic components impair the utilization of dietary iron. We examined the influence of the dietary polyphenols (-) -epigallocatechin-3-gallate (EGCG) and grape seed extract (GSE) on transepithelial iron transport in Caco-2 intestinal cells. The range of EGCG and GSE concentrations used in this study was within physiological levels and did not affect the integrity of differentiated Caco-2 cell monolayers. Both EGCG and GSE decreased (P < 0.001) transepithelial iron transport. However, apical iron uptake was increased (P < 0.001) by the addition of EGCG and GSE. The increased uptake of iron might be due in part to the reducing activity of EGCG and GSE. Both EGCG and GSE reduced approximately 15% of the applied Fe(3+) to Fe(2+) in the uptake buffer. Despite the increased cellular levels of (55)Fe, the transfer of iron across the basolateral membrane of the enterocyte was extremely low, indicating that basolateral exit via ferroportin-1 was impaired, possibly through formation of a nontransportable polyphenol-iron complex. Our data show that polyphenols inhibit nonheme iron absorption by reducing basolateral iron exit rather than by decreasing apical iron import in intestinal cells.
Full Article at the Journal of Nutrition:
http://jn.nutrition.org/cgi/content/full/138/9/1647
