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Using the best form of iron: fumarate vs glycinate

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What forms of iron are there?

In supplements, iron generally comes in the following forms:

  • Iron fumarate
  • Iron gluconate
  • Iron sulfate
  • Iron glycinate


The difference?

There are lots of different kinds of iron. The three most popular forms are iron fumarate, iron gluconate, and iron sulfate. Please keep in mind that the terms “ferrous” and “iron” are interchangeable when it comes to supplements.

Each of the three most popular forms of iron supplements is problematic. Iron is a tricky mineral to handle, but your body needs it. Forms of iron like ferrous sulfate, however, can do more harm than good. Research suggests that even a single dose of ferrous sulfate can cause oxidative damage, which means that daily dosing with this substance could cause irreparable harm.

Ferrous fumarate, for its part, may be harmful to people who have Crohn’s disease and other digestive conditions, and there are concerns about the bioavailability of this form of iron. Lastly, ferrous gluconate contains very little elemental iron despite the fact that it’s the most popular form of iron supplement.

Iron glycinate, however, belongs to a new class of nutrients called glycinates or bisglycinates. These types of supplement ingredients consist of essential minerals that have been bonded to glycine with citric acid, and they are far more bioavailable and less harmful than previous supplement-grade nutrient classes.



  • Iron fumarate has poor bioavailability and significant side effects
  • Iron gluconate contains hardly any elemental iron
  • Iron sulfate has terrible bioavailability, and it may be dangerous
  • Iron glycinate is new, safe, and highly bioavailable


Why is iron in glycinate form better?

Since they are relatively new, the science on glycinates like ferrous glycinate is nowhere near definitive. However, initial research suggests that ferrous glycinate could be as many as four times more bioavailable than iron sulfate, and this type of iron also appears to have a very mild side effect profile.

Simply put, glycinates are the next generation of essential mineral supplementation. Figuring out how to provide people with the essential minerals they need has always been a struggle since it’s relatively easy to overdose with these types of supplements. Especially for people with anemia, having easy access to safe iron supplements is a must, and iron glycinate represents the next leap forward in making iron safe and bioavailable.



  • Having access to safe forms of iron is a matter of life and death for some people, but iron gluconate, iron sulfate, and iron fumarate all disappoint in their safety and bioavailability
  • Ferrous glycinate, however, appears to be safe and vastly more bioavailable than other forms of iron.


Why do we use iron glycinate instead of other forms?

Our Feel Multivitamin™ is designed to be a supplement you can trust to get you through the day no matter what. Going into developing Feel’s earlier version of the multivitamin, we wanted to make a multivitamin that skipped all the nonsense and got straight to the point by delivering the nutrition you need.

Along the way, we learned that we hadn’t fully cracked the code when it comes to vitamins and minerals. Nutritional scientists are constantly determining new ways to make nutrients safer and more bioavailable, and here at WeAreFeel, it’s our vow to stay abreast of these industry developments to consistently bring you the best daily multivitamin ever devised.

The Feel Multivitamin™ is the next stage in the evolution of the best multivitamin in the world, and switching to ferrous glycinate is a big part of this upgrade. Enjoy your daily Feel Multivitamin™ knowing that it’s now equipped with the best form of dietary iron that science can (currently) devise.

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WeAreFeel Nutrition Team - All content provided on our blog is created exclusively for our readers by our research and nutrition team. We try to provide as much scientific backing as possible with references to support any claims made.
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