Best Iron Supplement?

  1. Iron Bisglycinate is regarded as the best iron formula because of high bioavailability and it shouldn’t cause gastric problems (including constipation). Iron bisglycinate (ferrous form of iron called Ferrous Bisglycinate) (HealthAid Iron Bisglycinate has 30mg per tablet with 120 mg Vitamin C which doubles absorption of iron) is a patented chelated form more effectively absorbed than other types of iron chelate. Regarded as better than other iron supplementations, including forms such as ferrous sulfate, as they can cause gastric problems nausea, constipation, and diarrhoea – due to lower absorption.
  2. The next type of iron supplement after Bisglycinate is probably Ferrous Fumarate found for example in Haemovit Plus which contains 50mg of highly absorbable Ferrous Fumarate per capsule. Haemovit Plus, however, might be too high in iron for an average person and should be recommended rather for individuals with already diagnosed iron deficiency or women with heavy menstruation as too much iron in the body leads to overproduction of free radicals. Ferrous Fumarate (best among ferrous irons) is better as far as bioavailability and tolerability is concerned as ferric forms (they have few times lower bioavailability). However, Iron Bisglycinate (also ferrous type) is regarded as better than Ferrous Fumarate because it doesn’t cause constipation, nausea and other gastric symptoms.
  3. Ferrous Gluconate (HealthAid Iron formula contains 17mg per 3 tablets) – lower bioavailability than fumarate.
  4. Iron Citrate (ferric type) has lower bioavailability than the ferrous forms but it is the best option among 3 different ferric irons as it doesn’t cause toxicity. Ferric Ammonium Citrate (Iron citrate) is found in Haemovit Gold.


There are two types of iron that are prescribed: ferric and ferrous iron.

The different forms of iron in supplements contain varying amounts of elemental iron. For example, ferrous fumarate is 33% elemental iron by weight, whereas ferrous sulfate is 20% and ferrous gluconate is 12% elemental iron. Ferrous sulphate preparations usually present good bioavailability (between 10 and 15%), while bioavailability of iron ferric preparations is 3 to 4 times lower than that of conventional FS. This is due to the extremely poor solubility of ferric iron in alkaline media and the fact that ferric iron needs to be transformed into ferrous iron before being absorbed.


According to Linus Pauling Institute:

ferrous fumarate is 33% elemental iron

ferrous sulfate monohydrate is 33% elemental iron

Ferrous sulfate heptahydrate is 20% elemental iron

ferrous gluconate is 12% elemental iron


Ferrous iron is better absorbed by the body than ferric iron. Three types of ferrous iron are typically prescribed: ferrous sulfate, ferrous fumarate, and ferrous gluconate.

Because ferric iron is not absorbed as well as ferrous iron, it is not prescribed as often. In addition, studies have shown that ferrous iron is tolerated better by patients than ferric iron. Because the gastrointestinal tract has less ability to reduce ferric iron to its ferrous form, there is a reduced chance of iron poisoning with iron citrate, which is the most commonly used form of ferric iron.


IRON BISGLYCINATE (Ferrous bisglycinate) is a patented chelated form of non-haem iron that passes through the stomach and small intestine without breaking apart. It has been shown to be more effectively absorbed than other types of iron chelate in healthy people with different iron levels. (Fairweather-Tait SJ, Wawer A, Gillings R, et al. Iron status in the elderly. Mech Ageing Dev 2014;136-137(100):22-28)

Conventional iron supplementation, including forms such as ferrous sulfate, can cause gastrointestinal side effects – including nausea, vomiting, constipation, diarrhea – because these conventional forms of iron are poorly absorbed. Iron Bisglycinate is high in elemental iron and should be combined with glycine and vitamin c for optimal absorption in the gastrointestinal tract, thus preventing the typical gastrointestinal side effects.

In the June 2000 issue of the Journal, Bovell-Benjamin et al (1) compared the absorption of iron from ferrous sulfate, ferrous bisglycinate, and ferric trisglycinate added to a whole-maize meal. They concluded that iron absorption was better from ferrous bisglycinate than from ferrous sulfate or ferric trisglycinate and that ferrous bisglycinate was an effective and safe source of iron that was particularly useful as an iron fortificant in diets rich in phytate.

Ferrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg according to a study.


Ferrous salts and in particular prolonged release FS preparations are the treatment of choice given their high effectiveness, acceptable tolerability, and low cost.

Preparations with iron III hydroxide polymaltose generally display poorer bioavailability and their clinical efficacy is yet to be established.

The claimed superiority of ferric iron preparations over sustained-release ferrous sulphate preparations is also questionable.

Ferrous and ferric iron salts, such as ferrous sulfate, ferrous gluconate, ferric citrate, and ferric sulfate.

Because of its higher solubility, ferrous iron in dietary supplements is more bioavailable than ferric iron. High doses of supplemental iron (45 mg/day or more) may cause gastrointestinal side effects, such as nausea and constipation.

Other forms of supplemental iron, such as heme iron polypeptides, carbonyl iron, iron amino-acid chelates, and polysaccharide-iron complexes, might have fewer gastrointestinal side effects than ferrous or ferric salts.

Fortunately, elemental iron is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of iron supplied by various forms of iron supplements.

Calcium might interfere with the absorption of iron. For this reason, some experts suggest that people take individual calcium and iron supplements at different times of the day.


There are two forms of dietary iron, “heme” iron and “non-heme” iron. Heme iron is iron bound to hemoglobin (the oxygen transporting protein in blood); non-heme iron is not bound to hemoglobin. Heme iron is the most efficiently absorbed form of iron.

The absorption rate of non-heme iron supplements, such as ferrous sulfate and ferrous fumarate, is 2.9% on an empty stomach and 0.9% with food. This is much less than the absorption rate of heme iron, as found in liver, which is as high as 35%. In addition, heme iron is without the side effects associated with non-heme sources of iron, such as nausea, flatulence, and diarrhoea.

Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron

Despite the superiority of heme iron, non-heme iron salts are the most popular iron supplements. One reason is that even though heme-iron is better absorbed, it is easy to take higher quantities of non-heme iron salts so that the net amount of iron absorbed is about equal. In other words, if you take 3 mg of heme iron and 50 mg of non-heme iron, the net absorption for each will be about the same. The best form of non-heme iron is ferrous succinate.


Vitamin C strongly enhances the absorption of nonheme iron by reducing dietary ferric iron (Fe3+) to ferrous iron (Fe2+) and forming an absorbable, iron-ascorbic acid complex.

Other organic acids: Citric, malic, tartaric, and lactic acids have some enhancing effects on nonheme iron absorption.


Elemental Iron Content

Iron supplements contain different amounts of elemental iron, which is the amount of iron that is available for absorption, depending on which form of iron is used in the supplement. For example, ferrous gluconate only contains 12 percent elemental iron, ferrous sulfate contains 20 percent elemental iron and ferrous fumarate contains 33 percent elemental iron.

Supplements containing ferrous fumarate and ferrous gluconate usually contain only half of the amount of elemental iron found in ferrous sulfate supplements due to the differing molecular weights of these types of iron, meaning you need to take twice as much to get the same dose of iron.

Side Effects

Iron supplements can cause side effects including diarrhea, vomiting, nausea, upset stomach and constipation. Slowly working up to the full dose can limit these side effects, as can taking iron with food. However, taking iron with some foods and beverages limits the absorption of the iron, especially if you take it along with dairy products, tea, cereal or coffee. While ferrous sulfate is the most commonly used type of iron supplement, switching to a different form of iron and lowering the daily dose may help limit side effects in some people while still gradually increasing iron stores.



Although you may be tempted by the coated and slow-release forms of iron supplements, since these don’t usually cause the same side effects as uncoated iron supplements, doctors don’t usually recommend them. They are more expensive as well as being less effective.