The same antioxidant compounds in dark grape juice that are noted for their health benefits in fighting heart disease may have a downside, according to new research in the Journal of Agricultural and Food Chemistry. In cell studies, scientists with the U.S. Department of Agriculture and Cornell University found that polyphenols in purple (also called red) grape juice can inhibit the uptake of iron, which could increase the risk of iron-deficiency anemia.
The findings still need to be confirmed in human studies, cautions the study's lead author, Raymond P. Glahn, Ph.D., a physiologist/nutritionist with the USDA's Plant, Soil and Nutrition Laboratory, located on the Cornell campus in Ithaca, N.Y. The study, which appears in the Nov. 6 issue of the journal, is the first comparative analysis among juices for iron uptake ability. The journal is published by the American Chemical Society, the world's largest scientific society.
While reducing iron can be beneficial for adults with certain medical conditions that involve excess iron, the same isn't necessarily true for young children. Iron-deficiency anemia can lead to mental, physical and behavioral impairment, particularly in infants and toddlers, say the researchers.
While iron-deficiency anemia is a major problem among children worldwide, youngsters in the United States are largely spared this problem by iron fortification of cereals, formulas and other foods, according to nutrition experts. Many children in this country, however, still do not get enough iron, notes Glahn.
Nonetheless, Glahn does not advocate removing dark grape juice from children's diets. Instead, he suggests limiting the amount.
"Since we don't know how much grape juice you have to drink to have an effect, I recommend alternating between dark and light juices. Don't just drink dark juices all the time," Glahn says.
"We're not saying, 'Don't drink grape juice,'" Glahn emphasizes. "We're saying, 'Here are some conditions that inhibit iron availability.'"
The study looked at the effect of various juices — red grape, white grape, prune, pear, orange, apple and grapefruit — on the ability of intestinal cells to absorb iron.
Using a novel laboratory model comprised of human intestinal cells, the researchers simulated conditions of digestion (including digestive enzymes and acidity) to compare the juices.
Dark grape juice reduced iron availability by 67 percent, while prune juice produced a 31 percent reduction. Light-colored juices, on the other hand, actually had the opposite effect; they increased iron uptake. Pear juice produced the highest uptake levels, followed by apple, orange, grapefruit and white grape juices.
Getting proper amounts of iron is particularly important for infants and children, as the mineral is essential for normal physical and mental development, whereas adult males and post-menopausal women generally get sufficient amounts of iron. Insufficient amounts of dietary iron, the number one nutritional disorder in the world, can lead to iron-deficiency anemia. This condition is characterized by excessive tiredness, decreased work and school performance, and decreased immune function, among others.
Iron metabolism differs among individuals. For the best advice on addressing the specific nutritional needs of children and adults, see a doctor or nutritionist.
The USDA funded this study.
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