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Do Your Genes Make You Absorb Too Much Iron?

Hemochromatosis is an inherited genetic disorder that results in excessive iron absorption and accumulation. Over time, the build-up of iron in vital organs makes people sick and more susceptible to cancer, diabetes, and liver failure.

An estimated 1 of every 200 to 500 people in the United States has genes that can lead to increased iron accumulation, and about 1 percent of those eventually develop symptoms of hemochromatosis. Geneticists characterize these people as “homozygous” because they carry two copies of the altered or mutated gene—one from each parent.

But what about people who carry only one copy of the altered gene? This is surprisingly common, occurring in an estimated 1 of every 10 people in the United States, especially those of Northern European origin.

Nutritionist Janet R. Hunt and molecular biologist Huawei Zeng, with the ARS Grand Forks Human Nutrition Research Center, Grand Forks, North Dakota, have conducted studies to determine whether individuals with only one copy of this genetic mutation could also be at risk of absorbing too much iron.

Those who carry one normal gene from one parent and one mutated gene from the other parent are “heterozygous” and are often called “carriers.” That’s because even though their one normal gene protects them from getting hemochromatosis, they can pass the mutation on to their offspring.

Hunt, who heads the center’s Micronutrient Absorption and Metabolism Unit, collaborated with Zeng to determine whether carriers also absorb more iron than usual. “If so, then the common practice of fortifying foods with iron could pose a health risk for them,” says Hunt.

For this genotyping study, Hunt and Zeng tested 359 volunteers by taking DNA samples either from the inside of their cheeks or from blood. Those identified as carriers had their iron absorption measured from regular and iron-fortified meals. Carriers of the mutation did not absorb iron differently than volunteers without the mutation, whether or not the meal was iron fortified. This was true for both forms of iron commonly found in foods: “heme” iron, from meat, poultry, or fish; and “nonheme” iron, found in plant foods as well as animal foods.

The researchers determined that carriers of this particular DNA mutation don’t need to worry about absorbing too much iron. “The study supports public health policies that allow addition of iron to foods to help those at the other end of the scale, who may be at risk of too little iron,” says Hunt.—By Rosalie Marion Bliss, Agricultural Research Service Information Staff.

This research is part of Human Nutrition, an ARS National Program (#107) described on the World Wide Web at www.nps.ars.usda.gov.

Janet Ross Hunt is with the USDA-ARS Grand Forks Human Nutrition Research Center, 2420 2nd Ave., Grand Forks, ND 58202; phone (701) 795-8328, fax (701) 795-8220.

"Do Your Genes MakeYou Absorb Too Much Iron?" was published in the May 2005 issue of Agricultural Research magazine.