Mar 05, 2007

Ironing It Out: Linking Diabetes with Iron Intake

Amy Campbell

If you’re old enough, you might remember those Geritol ads on television, proclaiming that everyone could be suffering from "iron-poor blood." But, in general, iron is one of those minerals that doesn’t get much respect. It’s just not that exciting—unless you happen to be iron deficient.

Iron is one of the most abundant minerals on earth. In the human body, it's needed as part of enzymes and proteins involved in carrying oxygen to cells and for regulating cell growth. Two-thirds of the iron in our bodies is found in hemoglobin, which is a protein in red blood cells that carries oxygen to our tissues. (In case you're wondering, hemoglobin A1c, or HbA1c, is a measure of how much glucose is attached to hemoglobin.) The rest of the iron in our bodies is found in myoglobin, a protein that delivers oxygen to muscle tissues, as well as in proteins that can store iron for future needs.

There are two forms of iron: heme iron, which is found in animal foods, such as red meat, fish, and poultry, and nonheme iron, found in plant foods, including lentils, beans, molasses, and spinach. Eating foods rich in vitamin C can enhance absorption of nonheme iron, while calcium, tannins (found in tea and other foods), and phytates (found in beans and other foods) may inhibit nonheme iron absorption. Here are the Recommended Daily Allowances for iron for adults: 18 milligrams (mg) for women of childbearing age, 8 mg for postmenopausal women, and 8 mg for adult men. So, as we age, our iron needs decrease.

Iron deficiency is a global problem, affecting about 80% of the world's population, while 30% of the population has iron deficiency anemia. Pregnant women, infants, toddlers, teenage girls, women of childbearing age, and people with kidney and gastrointestinal disorders are at risk for iron deficiency anemia. That pretty much leaves healthy teenage boys, men, and postmenopausal women who aren't at risk.

You might be wondering what the link is, then, between iron and diabetes. First, there's evidence now that women who consume too much heme iron (the kind found in animal foods) have as much as a 28% increased risk of developing Type 2 diabetes. This research, published last year, is based on a study of over 85,000 middle-aged women over a 20-year time frame. Another study from 2004 showed similar results: About 33,000 healthy women with high iron stores followed for 10 years had a significant increase in the incidence of Type 2 diabetes. The thought is that high iron levels may cause damage to muscle tissue, thereby decreasing the body's ability to move glucose from the blood into cells and also interfering with insulin production. (By the way, there's evidence that 50% to 80% of people with hemochromatosis, a disorder of iron absorption, go on to develop Type 2 diabetes.)

Secondly, there's new evidence that women with Type 2 diabetes who consume a high amount of heme iron and red meat have up to a 50% increase in the risk of coronary heart disease. The authors of this study admit that foods rich in heme iron (such as red meat) can also be high in saturated fat, which we already know is linked with heart disease. They also point out that foods high in heme iron don't necessarily "cause" heart disease; they're just "associated" with heart disease. All in all, though, they suggest that it's not a bad idea for people with Type 2 diabetes to cut back on their intake of heme-iron–rich foods. Maybe this information will encourage you to go easy on the steaks and burgers and try more meatless meals, such as beans and rice or lentil soup!

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