Iron Supplements Review
Initial Posting: 12/28/17 Last Update: 11/16/19
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What is It?
What It Is:
Iron is essential to manufacture hemoglobin, which enables red blood cells to transfer oxygen to the body's tissues. It is widely available in foods including meat, fish, grains and vegetables and the average diet provides sufficient iron (See What It Is
Symptoms of deficiency:
Iron deficiency (which is treatable with iron supplements) can cause symptoms such as fatigue, shortness of breath, dizziness, headache and pale skin. It is most common in menstruating women but also is commonly seen in children and pregnant women (few men are deficient in iron, and some may be at risk for iron excess
Iron supplementation may reduce unexplained fatigue in women of child-bearing age
who are not anemic but have ferritin levels in the lower end of normal range, inhibit dry cough associated with ACE inhibitors, and help to reduce symptoms of restless leg syndrome in people with low ferritin levels (see What It Does
Iron comes in many forms. If taken with just water, all are about equally well-absorbed, so less expensive forms, such as ferrous sulfate, are fine. However, with larger doses, some people experience gastric discomfort and/or constipation. Taking with food may reduce discomfort, but also reduces absorption of certain forms of iron, such as ferrous sulfate, while other forms are better absorbed in the presence of food, such ferrous bisglycinate and ferrous glycinate. Note that some supplements include vitamin C to increase iron absorption but this is unlikely have a significant effect, and there is concern that slow- or timed-release products may lead to reduced absorption of iron (see Forms of Iron and Avoiding Stomach Upset
One product was Not Approved for failing to disintegrate within the required time (See What CL Found
). Among the products that passed testing and were "Approved" for their quality, CL selected its Top Picks
based on quality, cost, dose, and absorption.
How much to take?
For correcting iron-deficiency anemia in adults: 100 mg to 200 mg daily, divided into two or three separate doses; this should be done only under physician supervision. When used as a treatment for other conditions, doses between 40 mg and 250 mg have been used. Unless treating a deficiency or specific condition, limit your daily intake of iron from supplements and fortified foods to no more than 45 mg to avoid side-effects and the harmful effects of excessive iron. Iron can also interfere with certain drugs. (See How much to take?
and Concerns and Cautions
Don't take iron with tea, as well as other minerals, as this may decrease iron absorption (See What to avoid when taking
Iron is an essential mineral that the body requires in small amounts. It is widely available in foods including meat, poultry, and fish, as well as dried fruits, grains, and green leafy vegetables. Iron from plant sources is absorbed half as well as that from animal sources. The average diet provides about 10 to 20 mg of iron per day.
What It Does:
Iron Deficiency and Anemia
Iron is needed to manufacture hemoglobin, which enables red blood cells to transfer oxygen to the body's tissues. Severe or prolonged iron deficiency is the leading cause of anemia in the United States, affecting about five percent of women and two percent of men. Symptoms of iron deficiency anemia include easy fatigability, shortness of breath, dizziness, headache, coldness of hands and feet, pale skin, chest pain, weakness, and lethargy. Other symptoms can include brittle nails, swelling or soreness of the tongue, cracks in the sides of the mouth, loss of taste, an enlarged spleen, and frequent infections. Iron deficiency has also been associated with recurrent aphthous stomatitis (canker sores) (Akintoye, Dent Clin North Am 2014). Some people with iron-deficiency anemia develop restless legs syndrome (see more about this in Benefits of Correcting Iron Deficiency below). Iron deficiency anemia can also cause irregular heartbeats (arrhythmias), a heart murmur, an enlarged heart, and heart failure (Kettaneh, Appetite 2005; NIH, 2014).
Iron deficiency is most common in menstruating women but also is commonly seen in children and pregnant women. According to the CDC, 9.5% of women 12 - 29 years are deficient, as are 6.7% of children ages 1 to 5. There are higher rates of iron deficiency in Mexican-American children aged 1 to 5 years (11%) and in non-Hispanic black (16%) and Mexican-American women (13%) of childbearing age (12 to 49 years) when compared to other race/ethnic groups. Low iron levels also may result from excessive bleeding, burns, and hemodialysis, as well as stomach and intestinal problems. Drugs that reduce stomach acid may also impair iron absorption (see What to avoid when taking).
During pregnancy, iron deficiency can result in preterm delivery and low-birth-weight babies.
Among children, iron deficiency is most common from ages 6 to 24 months, where it can cause developmental and behavioral problems. If iron deficiency is extremely severe, some of these problems can be irreversible.
Although few men are deficient in iron, 29% are at-risk for iron excess (CDC 2012).
Benefits of Correcting Iron Deficiency
Some evidence suggests that even mild iron deficiency, too mild to cause anemia, may cause fatigue and impair sports performance. Iron supplementation has been shown to reduce unexplained fatigue in women of child-bearing age who are not anemic but have ferritin levels in the lower end of normal range (less than 50 ug/L) (ferritin is an indicator of total iron stored in the body). A 12-week study of 198 such women (ages 18 to 53) found that those who received 80 mg of iron from ferrous sulfate daily from a time-release pill experienced a 47.7% decrease in fatigue, compared to a 28.8% decrease in the placebo group — a significant difference (Vaucher, CMAJ 2012), although there was no significant effect on anxiety or depression. Ferritin levels increased by 11.4 ug/L compared with placebo.
Among blood donors with normal hemoglobin levels, low-dose iron supplementation (37.5 mg of iron as ferrous gluconate daily) reduces the time by more than half for hemoglobin and ferritin levels to recover after donating a unit of blood. A study showed that those receiving iron recovered most of their decrease within about 30 days versus 78 to 158 days for those not receiving iron, depending on whether their ferritin levels were initially high or low. For those getting the iron supplement, ferritin levels returned to normal within 76 days while 67% of those not receiving supplementation had not fully recovered iron stores after 168 days -- when the study ended (Kiss, JAMA 2015). The researchers noted that although the hemoglobin decrease after donation is relatively small (about 10%) and of marginal clinical significance, for frequent donors it is important to be recovered before the next donation; suggesting that the current waiting period of 8 weeks (56 days) in the U.S. may be too short.
Verbal learning and memory have been shown to improve when adolescent girls with iron deficiency (although not anemia) are treated with iron supplementation (Bruner, Lancet 1996).
Unfortunately, among patients with heart failure and iron deficiency, giving high-dose iron (150 mg as iron polysaccharide) twice daily for 16 weeks did not improve peak oxygen uptake nor exercise capacity (6-minute walking distance) and only minimally improved iron levels (a 3% increase). A possible reason for the failure (which was not expected, as iron given intravenously in such patients raises iron by about 70%), was abnormally high blood levels in these people of hepcidin, an iron regulatory hormone that lowers iron levels by reducing iron absorption and trapping iron in while blood cells and liver cells (Lewis, JAMA 2017).
People with low or deficient levels of iron may be more likely to suffer from restless legs syndrome. Guidelines from the American Academy of Neurology advise that taking 65 mg of iron (from 325 mg ferrous sulfate) and 200 mg vitamin C (to help with iron absorption) twice daily may improve symptoms in individuals with restless legs syndrome who have ferritin levels below 75 ng/mL (Winkelman, Neurology 2016). This recommendation is based on a small study that gave a similar treatment (although half the vitamin C: 100 mg twice daily) to older men and women with low-normal blood ferritin levels (15 - 75 ng/mL) for three months. The severity of restless legs symptoms decreased by an average of 10 points on a scale of 0 to 40, while it decreased by just 1 point among those who took a placebo (Wang, Sleep Med 2009). Overall quality of life, however, did not improve in either group. Taking the iron increased blood ferritin levels from an average of 40 ng/mL to 65 ng/mL. Be aware that restless legs syndrome may also occur as a result of hereditary hemochromatosis (a disorder in which too much iron is absorbed from the diet and ferritin blood levels can get too high) and this treatment would not seem appropriate in such a situation (Cotter, Ther Clin Risk Manag 2006).
Iron supplements have shown some promise for reducing the dry cough caused by drugs in the angiotensin-converting enzyme inhibitor family (ACE inhibitors).
A small study of iron in children with ADHD showed improvement in some symptoms comparable to that with stimulant medicines (Konofal,Pediatr Neurol 2008).
A lower risk of suffering PMS (premenstrual syndrome) has been associated with a high intake of iron (over 20 mg per day) from supplements or plant-based foods (as opposed to meats) (Chocano-Bedoya, Am J Epidem 2013). Compared to women with the lowest daily intakes of iron (median of 9.4 mg) from these sources, the risk of PMS was reduced by 29% among those with a median intake of 21.4 mg, and by 36% among those with a median intake of 49.2 mg. Interestingly, the same study found that women consuming higher amounts of potassium from their diet (median intake of 3,717 mg daily) had a higher risk of PMS than those consuming less potassium.
See ConsumerTips for information about the forms of iron in supplements and dosage.
Quality Concerns and What CL Tested For:
In 1997, the U.S. Food and Drug Administration (FDA) reported that several iron-containing supplements had been recalled because of excessive levels of lead. Subsequent testing by ConsumerLab.com similarly found some iron products to be contaminated with lead -- a potentially harmful contaminant. However, tests by ConsumerLab.com since 2011 have found few instances of lead contamination, although some supplements have been discovered to contain less than their claimed amounts of iron.
Because no government agency is responsible for routinely testing iron supplements for their contents or quality, ConsumerLab.com independently evaluated iron products to determine whether they contained the iron stated on their labels. Products containing whole herbs and/or 250 mg or more of minerals per daily serving were also tested for contamination with lead, cadmium and arsenic. Iron tablets and caplets that were not chewable or time-release were additionally tested for their ability to break apart ("disintegrate") as needed for absorption. (See Testing Methods and Passing Score.)