Iron, an essential nutrient, has long been the nation's most common nutritional deficiency. In decades past, many parents worried that children who were picky eaters would develop iron-deficiency anemia. My mother boiled meat I refused to eat and fed me the concentrated broth in hopes I'd get some of its iron.
Now baby foods, infant formula and many other child-friendly foods, like breakfast cereals, breads, rice and pasta, are fortified with iron.
Today iron deficiency is more likely in infants who are exclusively breast-fed, young children who consume too much milk, menstruating and pregnant women, vegans and strict vegetarians and people who take medications that cause internal bleeding or interfere with iron absorption.
These days, more attention is being paid to the opposite problem: iron overload, which studies indicate can damage organs and may increase the risk of diabetes, heart attack and cancer, particularly in older people.
In examining more than 1,000 white Americans ages 67 to 96 participating in the Framingham Heart Study, researchers found that only about 3 percent had deficient levels of iron in their blood or stored in their bodies, but 13 percent had levels considered too high.
The authors concluded that “the likely liability in iron nutriture in free-living, elderly white Americans eating a Western diet is high iron stores, not iron deficiency.”
Iron is an essential part of the proteins that transport oxygen in the body. Hemoglobin, the oxygen-carrying protein in red blood cells, accounts for about two-thirds of the body's iron supply. Smaller amounts are found in myoglobin, the protein that supplies oxygen to muscles, and in enzymes needed for various biochemical reactions.
In addition, a varying amount of iron is stored in proteins that release it to the blood when needed. The more iron that is absorbed from the diet, the higher the level of stored iron.
About one person in 250 inherits a genetic disorder called hemochromatosis that increases iron absorption and results in a gradual, organ-damaging buildup of stored iron, although symptoms of the problem usually don't become apparent until midlife or later.
Factors affecting iron absorption
Iron deficiency can result in a confusing array of symptoms, including fatigue and weakness, poor work performance, increased risk of infections, difficulty keeping warm, lightheadedness, rapid heartbeat and shortness of breath with exercise. Studies have suggested that people who engage regularly in strenuous exercise, especially adolescents and vegetarians, are at increased risk of developing iron-deficiency anemia.
Iron deficiency is rare in men and postmenopausal women, and most should avoid supplements containing iron to reduce the risk of organ damage from too much iron. Also, if a routine blood test indicates low iron, experts warn against simply taking a supplement. Rather, a doctor should first check for hidden blood loss or impediments to iron absorption resulting from diet habits, medications or chronic health conditions, like colitis or the aftermath of weight-loss surgery.
There are two kinds of dietary iron, heme and nonheme. Heme iron, found only in meat, fish and poultry, is much better absorbed that the nonheme iron found in vegetables, fortified foods, supplements and acidic foods cooked in cast-iron pots. Whereas 15 to 30 percent of heme iron consumed is absorbed, only 5 percent of nonheme iron gets into the blood. To assure adequate iron absorption, some vegans and vegetarians may need to take a supplement.
Various factors can affect iron absorption. Some vegetables, like spinach (Popeye notwithstanding), contain oxalic acid, which interferes with iron absorption. High-fiber foods like whole grains that contain phytates and foods high in calcium also diminish the amount of iron that enters blood. But the vitamin C and other acids naturally present in fruits, fruit juices and some vegetables increase iron absorption.
In a subsequent study by the Framingham researchers, men and women ages 68 to 93 had the highest levels of stored iron if they consumed red meat four or more times a week, took more than 30 milligrams of an iron supplement daily or ate more than 21 servings of fruit each week. However, levels were much lower among those who consumed more than seven servings of whole grains each week.
Hazards of iron overload
Earlier this year, Nutrition Action Healthletter, published by the Center for Science in the Public Interest, summarized the latest evidence for the effects of excess iron stores.
The problem with too much stored iron is that, short of bleeding, the body can't easily get rid of it. Menstruating women are unlikely to have a problem, but for others with high stores the recommended treatments include phlebotomy and frequent blood donation. Without these measures, excess iron is deposited in the liver, heart and pancreas, where it can cause cirrhosis, liver cancer, cardiac arrhythmias and diabetes.
These health consequences can develop even in people without hemochromatosis, the genetic disorder, who accumulate very high levels of stored iron. For example, among 32,000 women followed for 10 years in the Nurses' Health Study, those with the highest levels of stored iron were nearly three times as likely to have diabetes as those with the lowest levels. Likewise, among 38,000 men in the Health Professionals Follow-up Study, those who consumed the most heme iron had a 63 percent greater risk of developing diabetes.
While the risk of cancer from too much iron is uncertain except in people with hemochromatosis, the known links between high levels of red meat consumption and cancers of the colon and prostate are highly suggestive of an increased risk associated with excessive consumption of heme iron.
As for heart disease, the link found in some studies to high levels of heme iron consumption may reflect the effect of saturated fats from red meat, the richest source of heme iron, more than that of iron itself.
High levels of iron have been found in the brains of people with neurodegenerative diseases like Alzheimer's, Parkinson's and amyotrophic lateral sclerosis (Lou Gehrig's disease). But sick brain cells accumulate abnormal levels of minerals like aluminum, so iron in these cases may be an effect of brain disease rather than its cause.
Nonetheless, there are ample health and environmental reasons to limit consumption of red meat to no more than two or three times a week and to focus more on poultry, seafood and plant sources of protein.