Answer:

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 (sold as "Gentle Iron") 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. For more details see the Forms of Iron and Avoiding Stomach Upset section of our Iron Supplements Review. Also see our overall Top Picks among the iron supplements we tested.

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2 Comments

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Vicki17506
January 30, 2019

What about iron carbonyl such as EZ Melts?

ConsumerLab.com
February 4, 2019

Hi Vicki - You can find information about carbonyl iron in the "Forms of Iron and Avoiding Stomach Upset" section of the Iron Supplements Review: https://www.consumerlab.com/reviews/iron-supplements-review/iron/#carbonyl

Elizabeth17505
January 30, 2019

I am surprised you did not mention carbonyl iron. It is the only type of iron that I have been able to take without significant gastric discomfort.

ConsumerLab.com
February 6, 2019

Thank you for sharing this, Elizabeth, it may helpful to other members. As noted in our response above, carbonyl iron is discussed in the "Forms of Iron and Avoiding Stomach Upset" section of the Iron Supplements Review: https://www.consumerlab.com/reviews/iron-supplements-review/iron/#carbonyl

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