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United States Department of Agriculture

Agricultural Research Service

Grand Forks Study Confirms You Can't Fool Mother Nature!
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Janet Hunt

Many people, when they think of nutrients like vitamins and minerals, think only in terms of getting enough. And since such nutrients are essential for normal well-being and function, and a little is good, then more must be better, right? Wrong! Nutrition is not just about getting as much of the good stuff (vitamins, minerals, phytochemicals) and as little of the bad stuff (Calories, fat, cholesterol) as possible. Rather it is about balance eating a variety of foods, containing a variety of components (some that have not even been specifically identified) that the body needs in moderate amounts and proportions for good health.

Iron is a case in point. Iron deficiency is often listed as the most common nutrient deficiency in the world. Iron deficiency anemia affects work capacity, by reducing the blood hemoglobin that is necessary for the transport and utilization of oxygen. Iron deficiency in pregnant women is associated with a greater likelihood of low birth weight infants. In infants and young children, iron deficiency adversely affects mental development and behavior. In the US, iron deficiency anemia affects 5% of women 20-49 years old. Moderate iron deficiency is most common in 1-2 year-old children (9%), and females 12-49 years old (9-11%), reflecting rapid growth or menstrual iron loss. Iron deficiency is much less common in males or older adults.

But before you reach for an iron supplement, consider the other side of this double-edged sword. Iron supplements intended for other household members are the most common cause of pediatric poisoning deaths in the US. In populations of European origin, approximately 1 in 300 people have hemochromatosis, a genetic abnormality of excessive iron stores that results in liver damage and higher rates of several cancers. Ten percent of these populations are carriers of the gene for hemochromatosis. Scientist are testing hypotheses that high iron stores may increase everyone's risk of chronic diseases, such as cancer and heart disease.

We recently tested the effects of iron supplements on the body's control of iron absorption. Fifty-seven men and women from the Grand Forks community, who had normal blood measures of hemoglobin and iron stores (serum ferritin) took iron supplements or placebos daily for 12 weeks. Iron absorption from a meal of hamburger, French-fries, and a vanilla milkshake was measured before and after supplementation. Daily iron supplements caused these volunteers to absorb 25% less iron from their food. But, this apparent compensation did not completely prevent more body iron. Iron stores ended up higher than in the placebo group, and stayed that way for at least 6 months after supplementation ended (as long as the study lasted). So, people who have adequate iron attempt to reduce their absorption of more iron than is needed, but only partly succeed.

Men and postmenopausal women should not be trying to fool Mother Nature by taking more iron. It is not difficult for men and postmenopausal women to get enough iron from ordinary foods. They should not be taking additional iron as nutrient supplements or as "super" foods that promise 100% of the RDA for all nutrients in a single food. Some nutrient supplements may be useful for some people (examples: calcium for women who don't drink milk, folic acid for women of child-bearing age, or vitamin B-12 for people who eat no animal products). However, the best strategy for a healthy diet is to consume a variety of foods, following the USDA food guide pyramid, and the goal of including 5 servings of fruits and vegetables daily.


Last Modified: 10/23/2006
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