Generations of Americans have been exhorted to eat spinach or liver for the iron that supposedly made Popeye's muscles bulge or to take iron-rich tonics like Geritol to revive their "tired blood."
But while some iron in the diet is critical for health and life itself, the overconsumption or overabsorption of this well-known mineral is now under intense scrutiny as a possible cause or contributor to killer ailments like heart disease and cancer as well as serious infections.
The story of iron is a classic illustration of "Just because a little is good does not mean more is better." Iron is essential to the formation of the oxygen-carrying pigments: hemoglobin in the blood and myoglobin in the muscles.
But people should not take iron supplements or stuff themselves with iron-rich foods unless medical tests have demonstrated an iron deficiency, those who study iron overload warn.
Some researchers are also concerned about the widespread use of vitamin C supplements, which can enhance the absorption of dietary iron when both are present in the gut at the same time. And questions have been raised about the wisdom of fortifying cereals and bread with iron in a country like the United States where a lot of iron-rich meat is consumed by most people.
The body has an imperfect mechanism for regulating the amount of iron people absorb and store in their tissues. Iron overload may result when the diet is overly rich in iron, from, say, the consumption of lots of red meat or supplements when the body is not iron-deficient.
Laboratory and clinical evidence suggests that an excess of iron in the tissues can promote coronary artery disease and foster the growth of latent cancers and infectious organisms.
Foods and supplements are not the only source of iron. It can also be inhaled, and smokers (tobacco leaves are rich in iron) as well as workers in industries that spew particles containing iron into the air may risk lung cancer in part because their lungs are chronically exposed to excess iron.
The body has only one way to rid itself of iron, through bleeding, which is why symptoms of iron overload do not usually show up in menstruating women until after menopause. Bleeding may also contribute to the protection against heart disease and colon cancer associated with vigorous exercise and the regular use of aspirin and related drugs; both cause the repeated loss of tiny amounts of blood from the digestive tract.
For at least 1.5 million Americans who have a genetic disorder called hereditary hemochromatosis, there is no question that even moderate amounts of dietary iron can lead to accumulations of "rust" in organs throughout their bodies. Unless this disorder is identified before it causes serious organ damage and treated by frequent blood-letting, it can result in such potentially fatal conditions as heart disease, cirrhosis or cancer of the liver as well as thyroid disease, diabetes, arthritis and infertility.
In the early stages of hemochromatosis, symptoms like chronic fatigue, abdominal pain, impotence and menstrual disruption mimic so many other conditions that doctors often miss the correct diagnosis until vital organs are irreparably damaged.
Although many doctors now in practice were taught that this is a rare condition that occurs primarily in white males of northern European descent, it is now known to be the most common genetic abnormality, surpassing the combined cases of cystic fibrosis, phenylketonuria, or PKU, and hereditary muscular dystrophy and occurring equally in men and women.
But because most women menstruate for 30 or 40 years, the problem may not show up in women until after menopause. Furthermore, it has now been shown to occur as frequently in Hispanics as in non-Hispanics in the United States. A related genetic condition has also been identified in African blacks, but its incidence has not yet been studied in African-Americans.
Last summer, researchers at Mercator Genetics Inc., a gene discovery company in Menlo Park, Calif., reported identifying the gene that appears to cause hereditary hemochromatosis, a finding that could lead to a simple screening test for this disorder before it results in serious consequences.
Hemochromatosis, which is inherited as an autosomal recessive trait, like blue eyes and PKU, requires the presence of two abnormal genes, one from each parent, to cause the condition. One in 10 Americans is believed to carry one abnormal gene; if two such people have children, one in four of their offspring, on average, will have hemochromatosis and half will themselves carry the gene and be able to pass it to their own children.
There is growing evidence that even people without an inherited disorder can develop problems associated with iron overload. Iron is a catalyst for the formation of free radicals, highly active chemicals that are implicated in heart disease, cancer and the aging of cells.
Dr. Eugene D. Weinberg, a professor emeritus of microbiology at Indiana University in Bloomington who has studied the effects of iron for three decades, is one of a number of researchers who have warned that an overabundance of iron could be undermining the health and shortening the lives of millions of Americans.
Cancer needs iron
In an interview, he pointed out that both cancer cells and infectious organisms need iron from their host to grow. Cancer cells can live in a semidormant state for a long time, he explained, but they cannot multiply without iron and oxygen from blood. He said smokers, asbestos workers and people who grind or weld steel, mine iron or paint with iron oxide powder could acquire high levels of iron in their lung tissues, increasing their risk of lung cancer.
Weinberg added: "Every pathogen needs iron, which it must get from its host. If there is excess iron in the tissue the pathogen is growing in, it will foster multiplication of the pathogen." For example, one study found that the bacteria that cause Legionnaire's disease would not survive if the level of iron in lung cells was very low.
As for heart disease, a study conducted among 1,900 middle-age men in Finland indicated that a high iron level was second only to smoking as a cause of heart attacks. Although three American studies failed to confirm or refute this finding, the methods used in these studies were less precise.
The Finnish researchers found that the greatest risk of having high iron occurred in men with high cholesterol levels. In those with low cholesterol, iron had no impact on the risk of heart attack, suggesting that iron's role in heart disease may involve the oxidation of low-density lipoprotein -- LDL, the "bad" cholesterol -- into the form that clogs up arteries.
A person's iron status can be checked through several blood tests. The most useful is a ferritin test, which can be done as part of a routine blood test.
Pub Date: 3/11/97