When is too much iron a bad thing? Not that often: Most Americans are more likely to be iron-poor (which leads to anemia) than overabundant in the metal. Yet there are folks with too much iron, notably those who suffer from hemochromatosis, an illness that can damage a variety of organs. The ailment is also associated with Type II diabetes. And that has led doctors to wonder: Is there something about iron itself that raises the risk of diabetes?
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Yes, at least among healthy middle-aged women, according to a new study from a group of researchers at Harvard School of Public Health and Harvard Medical School. It's the first study to take a large group of healthy people–about 1,400 women–and control for differences in age, race, obesity, diet, history of heart disease and other factors, and then follow these people for 10 years. The researchers also controlled for pre-existing inflammation–a condition that might exacerbate diabetes–by measuring markers of inflammatory disease in the blood.
After a decade, those most likely to develop diabetes were those with the highest stores of iron, the scientists report this week in the Journal of the American Medical Association. Women with the highest iron levels were almost three times as likely to have diabetes as women with the lowest levels. (The difference was measured by blood tests for ferritin, a protein that stores iron in the body, as well as another molecule that ferries iron around to various organs.)
Too much iron, roaming freely in the body, can damage cells because it creates free radicals, those reactive molecules that attack cell membranes and DNA. And this may directly relate to diabetes. Studies have suggested that when iron accumulates in muscle it interferes with the ability to absorb glucose, because of cell damage. In addition, lots of iron in the pancreas can hamper insulin secretion. The excessive iron first leads to insulin resistance–a diabetes precursor–and then to a drop-off in levels of the vital hormone, and that's often the path to Type II diabetes.
This news should not send you running to toss out your Geritol or spinach. Iron deficiency is a real and widespread problem–the most common nutritional problem in the world, according to the World Health Organization. But the researchers do suggest that for women who are at risk for Type II diabetes for some other reason–obesity, say–having their blood tested for excess iron would be worthwhile. High iron could be a warning that such people should reduce other risk factors, such as their weight.
