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Iron Supplementation


Inexpensive, convenient and widely available, oral iron supplements effectively correct uncomplicated iron deficiency anemia.   A number of oral preparations are available, differing in the chemical state of iron, the type of its salt, dosage, and pharmaceutical formulation (tablets, liquid, quick or slow release). Intravenous iron injections are also available as an alternative for people who cannot tolerate or are unresponsive to oral supplements.


Many iron supplements are available over the counter but do not be tempted to start taking iron without your doctor’s guidance. Remember, iron is an essential micronutrient, but it can be harmful if taken in excess! Consult your doctor about the type of iron supplementation that is right for you.

The supplement you select will depend on your specific situation –the reason for and the extent of your deficiency, your age, gender and physical condition. 

Iron supplements, types, advantages

Ferrous (Fe2+) or ferric (Fe3+) salt or something else?  In our body, iron is found in one of two oxidation forms, ferric (Fe3+) and ferrous (Fe2+).  Iron can easily shift between these two states. For example, iron changes from ferric to ferrous form in order to be absorbed by the cells in the gastrointestinal tract. Conversely, extra ferrous iron is converted to the ferric form for storing.


The majority of oral supplements contain iron in the same two states. Generally, ferrous salts offer better therapeutic efficacy over ferric salts and are less expensive.   For this reason, the most commonly used iron supplements are ferrous salts, such as sulfate, gluconate, and fumarate.


Relatively novel iron preparations such as heme iron polypeptide (HIC) or carbonyl iron (elemental, uncharged iron) aim to improve absorption and reduce side effects.  However, ferrous salts remain the most recommended and used oral supplements, as there is not enough evidence to support the advantages of these newer, generally more expensive, iron preparations. 

Salt type and Dosage. For the most part, when taken as recommended, supplements containing different ferrous salts are equally effective in correcting iron deficiency. However, not all iron salts contain the same amounts of iron per dose. This means that different iron salts will require different dosing regimens in order to meet your doctor’s recommendation (see example below). Always check the label to see what type of iron (ferrous, ferric, heme, or uncharged iron) and how much of it is in your supplement! 




how to read iron supplement labels

In the above example, ferrous gluconate (A) contains 27mg of iron; ferrous sulfate (B) contains 65mg; and, polysaccharide iron complex (iron is in Fe3+, ferric state) and heme iron polypeptide (HIC) together (C) contain 28mg. If your doctor recommends 100mg of iron per day, you would have to take 4 pills of A, 2 pills of B and 4 pills of C to meet the recommended dose.


Solid or liquid? Oral supplements come in many formulations: liquid, tablets, capsules, and chewables. Adults most commonly use tablets. Liquid is well suited for children as it is easy to administer and can be “disguised” in food. Liquid supplements also offer an easy way to adjust the dose. Dose adjustments are very helpful for people who experience significant gastrointestinal side effects and cannot tolerate iron supplements. In those cases, instead of stopping the supplementation altogether, the dose should be reduced to the maximum tolerated level. 


Enteric coated, quick- or slow-release? Gastrointestinal side effects associated with oral iron therapy are very common and include abdominal pain, nausea, flatulence, diarrhea, constipation, etc. Enteric coated and slow-release supplements are an attempt to reduce these side effects by controlling the location and the amount of iron released. Indeed, enteric coated and slow-release iron supplements are better tolerated, but this comes at a cost. Most of the iron absorption takes place in the upper part of the small intestine, where enteric coated and slow-release supplements deliver only small amounts of iron. For this reason, enteric coated and slow-release preparations are not as therapeutically efficacious as their quick-release counterparts.   For an efficient and fast correction of iron deficiency, choose quick-release supplements.


How to use


Typically prescribed dose for adults is 100-200mg of iron a day, administered as two or three pills. To get an optimal amount of iron from your supplement, take it on an empty stomach between meals and at bedtime. If you experience gastrointestinal side effects, take the supplement with food. However, this will reduce its efficacy, so make sure you optimize it by avoiding the inhibitors and adding the enhancers of iron absorption. Vitamin C is the most powerful enhancer of iron absorption. Take your iron with freshly squeezed lemonade or orange juice that are rich in vitamin C and boost its absorption. 


Symptoms of anemia such as tiredness and weakness resolve quickly, usually within a week of oral iron therapy. However, do not stop iron supplementation after you begin to feel better. It will take a few months until your iron status goes back to normal.




Gastrointestinal side effects, such as nausea, abdominal pain, bloating, diarrhea, constipation and black stools are rather common. If side effects become too bothersome, talk to your doctor about ways to minimize them. Changing the type of supplement, dose or frequency, may greatly reduce gastrointestinal discomfort and allow for a successful continuation of the therapy.


Iron interacts with many drugs, such as antacids, antibiotics, bisphosphonates and others. Check with your doctor if the drugs you are taking interact with iron.


Iron supplements are extremely dangerous for young children. Always keep your supplements away from children.


Iron supplements


One of the least expensive and longest used supplement is ferrous sulfate.

USP (United States Pharmacopeia) certified supplements are available from Nature made.​

Last updated: October 23, 2016

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