Does Too Much Iron Clog Arteries?

The U.S. Food and Nutrition Board has set the new tolerable upper limit (UL) for dietary iron at 45 mg/day primarily on the basis of the adverse side effects (e.g., gastrointestinal pain and constipation) of iron supplements.1 However, these adverse gastrointestinal (GI) effects are unlikely to occur if this amount of dietary iron is exceeded provided it comes from iron fortified foods or foods rich in iron (liver, beef, clams and beans). While this upper limit is fine to avoid GI distress, most older individuals should not consume more than 10 mg per day.

Data from the NHANES III indicated that about 9% of toddlers and adolescents are iron deficient. And about 11% of women of childbearing age were also found to be iron deficient. This makes iron deficiency the most common nutritional deficiency in the US.2 Clearly, those individuals in these high-risk groups should be encouraged to consume iron-rich or fortified foods. By contrast, adult men and postmenopausal women are at low risk of iron deficiency.

In 1981, Sullivan was the first to propose that excessive iron stores may promote atherosclerosis and heart disease and could explain the much of the higher risk of cardiovascular disease in men relative to premenopausal women.3 More recently, two large, prospective epidemiological studies that were carefully controlled for confounding variables found increased iron stores correlated with a greater risk of cardiovascular disease in both men and women.4, 5 There is also growing evidence that excess iron stores can adversely affect glucose metabolism and may be particularly dangerous for those with insulin resistance and diabetes.6 Excess iron stores can also damage the liver and promote liver cancer.

Bottom Line: The new UL for iron is clearly too high for people with diabetes, dyslipidemia, atherosclerosis and/or liver disease. Men and older women should be discouraged from taking supplemental iron or using iron-fortified foods unless they can be shown to have low iron stores. This is particularly true for those with diabetes and those at high risk for CVD. If low iron stores are confirmed, iron supplements should be limited to 45 mg of iron because of adverse GI problems.

References:
1. Dietary reference intakes. Washington, D.C.: National Academy Press, 2001:9-1-78
2. JAMA 1997;277:973-6
3. Lancet 1981;1:1293-4
4. Am J Clin Nutr 1999;69:1231-6
5. Circulation 1998;97:1461-6
6. Diabetes 2002;51:2348-54

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