Iron through the ages – includes related information – aspects of iron nutrition
With so much attention being paid to dietary excesses, it’s easy to forget that iron deficiency and anemia are still widespread problems in Canada. Infants, children, adolescents, vegetarians and women are most at risk. Although no national statistics have been compiled since 1973, studies suggest that 20 to 30 per cent of premenopausal Canadian women have iron intakes below the Recommended Nutrient Intake (RNI) of 13 mg a day. Young children too are often low in iron. An estimated one to three per cent of 6 to 12 month old infants from middle income city families, and as many as 10 per cent of 18-month olds from low-income families, are iron-deficient. Iron deficiency can arise for many reasons – for instance, not getting enough from the diet, difficulties in absorbing it or through blood losses (from menstrual periods, bleeding ulcers or other causes).
Why our bodies need iron
Vital to health, iron has several key functions in the body. Best known is its role in transporting oxygen to the tissues. Nearly three quarters of the iron in the body occurs within a compound called hemoglobin – the pigment inside red blood cells that binds with oxygen and carries it to all body cells. Hemoglobin also helps remove carbon dioxide from blood to be exhaled, and iron-containing enzymes take part in various oxidation reactions and electron-transport mechanisms. Iron may also contribute to psychomotor and mental processes. (Lack of iron can lead to the condition known as anemia.)
Maintaining the body’s iron balance
In order to maintain a healthy iron balance, the body must absorb enough from the daily diet to offset the amounts lost in sweat and urine, in cells shed from the skin and interior surfaces (such as the intestines), and – in women – amounts lost by normal menstrual bleeding. On average, adults lose 1 to 2 mg of iron a day. To replace it, they must ingest much more from food because only a small proportion of dietary iron is absorbed. The human body conserves iron efficiently and gears absorption to the amount stored. Iron absorption is regulated so that the body absorbs only as much as it can safely use, to avoid “iron overload,” which can be dangerous.
The more iron stored in the body, the less is absorbed from food. Any extra iron is stored in the liver, spleen or bone marrow, ready for use if there should be a shortage. If dietary absorption isn’t enough for the body’s needs, iron is released from the stores to meet the shortfall. Absorption from food improves whenever iron stores are low. If a “negative” (low) iron balance is prolonged, iron deficiency – perhaps ultimately anemia (with red blood cells short of hemoglobin) – will develop. However, some people can remain marginally iron deficient for long periods without developing anemia.
What affects the body’s iron absorption?
Getting enough iron means more than just adding up the milligrams of iron in the foods eaten as not all is absorbed.
The amount of iron absorbed from food depends on: * The body’s iron status. When iron stores are low or if people are iron-deficient, the body absorbs more from food. Absorption also improves during growth spurts and pregnancy, when iron needs increase.
* The form of iron in the foods consumed. Iron from animal products is more readily absorbed than iron from plant foods.
* The mix of foods eaten. People can boost their iron absorption by being careful about the food combinations eaten. For example, vitamin C (in citrus fruits) enhances iron absorption, while the presence of calcium (in dairy products) inhibits it.
Different amounts absorbed from different foods
Curiously, although we tend to link spinach that’s “good for you” with Popeye the sailor man, the mineral is poorly absorbed from spinach and most other vegetables. In general, “heme” iron in animal products is better absorbed than “non-heme” or inorganic iron in plant foods. But the mix of foods eaten is the most crucial influence.
Heme iron – found in animal foods such as meat, liver, poultry and fish – is more easily absorbed and used by the body than non-heme iron in vegetables and grains. (Heme is the iron-containing part of hemoglobin.) Heme iron in meat and other animal products constitutes about 5 to 10 per cent of an average adult’s daily iron intake in most developed countries. The absorption of heme iron is influenced little by a person’s iron status (body stores).
Non-heme iron – the form we get from plant products such as cereals, fruits, vegetables and pulses (beans) – comes in a less absorbable form than heme iron. For example, while a serving of bran actually contains more iron than a steak, the body absorbs almost twice as much iron from the steak. Also, in contrast to heme iron, the absorption of non-heme iron is greatly influenced by a peron’s iron status – more non-heme iron is absorbed when people have low iron stores. Some 20 years ago, meat, fish and poultry were the main sources of dietary iron for Canadians. By contrast, in the 1990s, more comes form vegetarian sources. For instance, in the Nova Scotian diet most of the iron comes from pasta, rice, cereals and breads (44 per cent), less from meat, poultry and fish (23 per cent), the rest from vegetables. Whether these dietary shifts are widespread has yet to be determined.
Mix of foods eaten most critical
for iron absorption
The absorption of iron at any meal depends not only on its iron content and the form it’s in, but more importantly on the presence of other foods that enhance or reduce its absorption. For example, vitamin C or ascorbic acid increases the amount of non-heme iron that can be absorbed from plant foods. The inclusion of vegetables or fruits rich in vitamin C at a vegetarian meal may double or even triple iron absorption. The presence of heme iron from animal foods also enhances non-heme iron absorption. Eating a meat, fish, liver or poultry with plant foods can double or triple iron absorption. Conversely, the presence of certain compounds such as tannin (in tea) reduce the “bioavailability” of iron.
Foods that inhibit iron absorption
Some foods contain iron inhibitors of “ligands” that bind with iron and prevent in from passing through the gut (intestinal walls) into the bloodstream. Besides tannin in tea, other iron-inhibitors include phytates (found in unprocessed cereals and bran) and certain spices (such as oregano). Calcium also blocks iron absorption. As little as one glass of milk (about 165 mg on calcium) halves iron absorption, so experts recommend that people take calcium supplements between meals, and not at the same time as an iron supplement. In addition, certain foods can bind the non-heme iron in another food eaten at the same time. For instance, wheat and rice contain ligands that bind most of the non-heme iron in kidney beans.
Tips for getting more iron in your diet
* Eat a little meat, fish or poultry several times a week, but choose low-fat forms.
* Have some citrus fruit or juice with your breakfast cereal.
* Drink tea between rather than with or right after a meal.
* When eating vegetables or cereals high in iron, include foods rich in ascorbic acid.
* If you are a vegetarian, include ascorbic acid (vitamin C) sources such as citrus fruits, green peppers or cabbage at most meals.
* Take calcium supplements not with but between iron-rich meals.
* Don’t sprinkle raw wheat bran on foods, as it reduces iron absorption.
* Keep iron tablets well away from children who may mistake them for candy with dire consequences.
Infants may be at risk of iron deficiency
Whether healthy, full-term infants need iron fortified foods has long been a controversial topic. In full term newborns, breast milk and the body’s stores usually provide enough iron for the first 3 to 6 months after birth. Breast milk, although not rich in iron, contains it in a far more absorbable form than that in cow’s milk. Exclusive breastfeeding for the first six months often provides enough iron. However, prolonged breast or bottle feeding can produce iron deficiency – which is a widespread problem among infants and young children. In one study, the prevalence of iron deficiency (and iron-deficiency anemia) among healthy Canadian infants was 3.5 per cent for those six months old and 10.5 per cent for 18-month-olds. In another (Montreal) study, 24.3 per cent of 10- to 14-month-old babies from low-income families had iron-deficiency anemia. Reasons for iron deficiency in infants include prematurity, introducing cow’s milk before nine months of age and an iron-poor diet. Premature infants are at special risk because of their low iron stores at birth and rapid postnatal growth.
Meeting the iron needs of young infants
Healthy, full-term babies are born with enough iron for the first three to six months of life. However, within the first year of birth, an infant must triple its body weight and double its total iron content, the highest demand for iron occurring between six and 12 months. From the age of one to six years, the body’s iron content doubles once more. “This rapid growth and increase in hemoglobin can put infants and children at risk of iron shortage,” explains one expert in child nutrition. “But that does not mean every healthy full-term baby who is either breastfed or fed non-iron-fortified formula will become iron deficient. What’s most vital is to follow the current pediatric advice.”
The Canadian Pediatric Society recommends that breastfed babies be given iron-fortified infant cereals and other iron-rich foods starting at age four to six months, and iron-fortified formula for infants who are weaned before 9 to 12 months of age. Bottle-fed babies should have iron-fortified formula from birth until 12 months of age. After 18 months of age, the risk of iron-deficiency anemia diminishes as growth rates decline and the diet becomes more varied.
The recommended intake of iron for children aged one to three years is 6 mg a day – easily obtained from a varied diet that includes meat and plenty of vitamin C. However, some children remain at risk for iron deficiency, particularly those of Inuit, Indian and Chinese families. Risk factors include a low birthweight, low hemoglobin levels at birth, frequent infant infections, introducing cow’s milk before nine months of age, excessive tea intakes, vegetarian diets and a low consumption of vitamin C.
Premature and low birthweight babies need extra
Low-birthweight and premature infants have special requirements because of low iron stores at birth and a growth rate faster than full term babies. The Canadian Pediatric Society recommends an iron supplement be given to them beginning at eight weeks of age and continuing until the child turns one year old. Iron-fortified formula for bottle-fed infants or commercial iron drops for breastfed pre-term infants are recommended.
Women’s iron needs
Women are more likely than men to be iron deficient because of menstrual blood losses, weight-loss regimes and diets low in meat. In one Canadian study,m the mean intake or iron among women in Nova Scotia was less than 85 per cent of the RNI. Premenopausal women on vegetarian diets find it especially hard to meet their iron requirements. Once past menopause, iron deficiency is less common.
Iron needs go up during pregnancy to meet the increased blood volume and demands of the developing fetus. Iron requirements are greater during the second and third trimester than in the first, Even if a woman has high iron stores at the beginning of pregnancy, it’s generally believed that she cannot fulfil her iron requirements through diet alone during the last two trimesters. The current RNI for pregnant women is 18 mg per day during the second trimester, and 23 mg per day during the last trimester. If iron stores are inadequate, an iron supplement of 10 to 30 mg per day is advised after about the fourth month of pregnancy, or earlier in women who start pregnancy with low iron stores.
Can too much iron be harmful?
Too much iron can be as or more harmful than too little. However, since our bodies carefully regulate the amount of iron absorbed, for the great majority of people there is no risk of iron toxicity even from the largest amounts of iron that anyone is likely to ingest from food. One rare example of iron overload is described among Bantu populations that consume large quantities of beer brewed in iron containers. Iron overload has also been observed in alcoholics who consume a lot of iron-rich wine.
Hemochromatosis is a genetic disorder affecting people of European origin which disrupts the body’s natural iron regulation so that an excess builds up. People with hemochromatosis need medical supervision to prevent their bodies from becoming dangerously overloaded with iron.
Warning: The iron in vitamin-mineral supplements can threaten health if taken in excess, and the tablets may have dangerous, even lethal, results if accidentally eaten by children. Iron tablets look like candy and, if swallowed by children, can make them acutely ill with iron toxicity. So it is best to regard iron pills as “medicine” and lock them away beyond the reach of children.
Possible link between iron and heart disease
Recent studies have raised suspicions that a high blood ferritin (iron) level may increase cardiovascular risks. One study of 2,000 Finnish men who had very high blood iron concentrations and high heart attack rates led to speculation that iron raises the risk of heart attack, perhaps by promoting the formation of free radicals that lead to atherosclerosis (artery hardening). However, other factors could explain the increase in heart disease. Death rates from heart disease in Finland are among the world’s highest, attributed to a very high animal fat consumption. The Finns have higher blood LDL (“bad”) cholesterol levels than most Western populations, perhaps partly explaining their elevated heart attack rates. More studies are under way to investigate the connection, particularly as blood ferritin levels seem to be increasing among U.S. men.
Iron deficiency and iron-deficiency
anemia: What’s the difference?
Iron deficiency can develop because of an inadequate supply of dietary iron, because too little is absorbed or because of blood losses. Menstrual losses are a key cause of iron deficiency in women. Besides menstruation, other causes include uterine growths, gastrointestinal disorders, bleeding ulcers and hemorrhoids. In men typical causes of anemia include intestinal blood loss, stomach ulcers, cancer or a parasitic infection (e.g., hookworms). Iron deficiency usually starts slowly with gradual depletion of the body’s iron stores. As stores dwindle, iron absorption from food increases. But when the body’s iron stores are gone and the diet can no longer supply enough, the red blood cells may contain less hemoglobin and eventually get smaller, leading to iron-deficiency anemia.
In those who have anemia, the heart must work harder to supply enough oxygen. This extra load makes people look pale, feel weak and constantly tired, perhaps short of breath – typical signs of anemia. Severe anemia may lead to an irregular or increased heart rate. Besides nutritional iron deficiency and menstrual or other blood losses, different forms of anemia can arise for other reason – such a s faults in red blood cell formation, infections and genetic disorders (e.g., sickle-cell anemia). Anemia is cured not by iron supplements alone, but by treating the underlying cause(s). A physician should always be consulted if anemia is suspected.
Amounts of iron recommended at various ages
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