Iron Supplements: Ferrous Fumarate, Sulfate And Gluconate

Have you been told by your doctor to start taking iron supplements?

You may have been surprised to learn how many different kinds of iron supplements there are, among them being ferrous fumarate, ferrous sulfate, and ferrous gluconate.

So what’s the difference between these different types of iron? Does it matter which one you take?

Read below to find out why iron is important, reasons you may want to supplement, and what the difference is between these three types of supplements.

Importance of Iron

Most of the body’s iron, about 70%, is found within the blood and the muscles.

In blood, iron helps to form a protein that lives in red blood cells called hemoglobin. This protein transports oxygen through the blood stream.

In muscle, iron helps form a protein very similar to hemoglobin called myoglobin. Myoglobin also carries oxygen but works specifically with muscles.

Aside from carrying oxygen throughout the body, iron also makes up many of the enzymes found in the body. Enzymes help to speed up chemical reactions that are responsible for forming and breaking down molecules in your body like collagen, a protein important to the strength and flexibility of your skin.

Reasons To Take Iron Supplements

According to the World Heath Organization, iron deficiency is the most common nutritional disorder in the world. A deficiency of iron can eventually lead to anemia, a condition where there are lower levels of hemoglobin in the blood.

Your doctor or dietitian may put you on an iron supplement if you are iron deficient to prevent you from developing anemia. Once you develop anemia, higher levels of iron may be needed for a short period of time (usually about 3 months) to get your levels up to a normal amount.

Women are much more vulnerable to iron-deficiency than men. Men have about 3-years-worth of iron stored in their bodies, while women only have 6-months-worth.  Women who have a monthly menstrual cycle are even more susceptible because they lose iron during their bleed.

Iron can be found in foods like meat, seafood, dark leafy greens, and tofu. People with severe iron deficiencies or iron-deficiency anemia may not be able to bring their levels back up to normal using food alone, because iron is not very easily absorbed.

Women who are menstruating need 18 mg/day of iron, while men and post-menopausal women need 8 mg/day. Because of iron’s low bioavailability, iron supplements can much more iron than the daily recommended amount.

Symptoms of Iron-Deficiency

  • Trouble concentrating
  • Fatigue
  • Memory problems or brain fog
  • Spoon-shaped nails
  • Sore tongue
  • Cracks at the corners of your mouth
  • Restless Leg Syndrome
  • Pica – craving non-food substances like chalk, dirt, or clay

What’s the Difference Between Ferrous and Ferric?

Ferrous and ferric are simply different forms of iron.

Ferrous is the type of iron preferred by your body – this means it is more easily absorbed. Ferric iron must be converted into ferrous iron before the body can use it. While both still work, ferrous iron is usually the preferred type when selecting a supplement.

Ferrous Sulfate

Ferrous sulfate is an iron salt. The word salt refers to any substance that is a metal (like iron) combined with a nonmetal (like sulfate).

This form of iron is the easiest for your body to absorb. This is because sulfate is an organic molecule, meaning that it contains carbon. Organic molecules are easier to separate from inorganic molecules like iron, allowing your body to use them more efficiently.

Ferrous sulfate supplements contain more iron than gluconate and fumarate forms. This is helpful for people with deficiencies but can have a downside. Many people react poorly to higher amounts of iron and can experience nausea, vomiting, or stomach cramps.

If you react poorly to ferrous sulfate, your doctor may choose a different form or recommend that you take smaller doses throughout the day.

Ferrous Gluconate

If you do have issues with nausea while taking iron supplements, ferrous gluconate tends to be much better tolerated. Ferrous gluconate tablets contain less iron per dose than ferrous sulfate.

A downside of ferrous gluconate is that it is not as easily absorbed as the sulfate form. This is because gluconate is an inorganic molecule. Two inorganic molecules are harder for your body to break apart, meaning you will absorb less.

That being said, ferrous gluconate is still a good option – it has about 90% the absorption rate of ferrous sulfate.

Ferrous Fumarate

Ferrous fumarate is the least absorbable form of the three ferrous iron supplements. Like gluconate, fumarate is an inorganic molecule. This means your body has a harder time removing it from the iron.

This form of iron also takes longer to absorb. It must spend more time in your stomach so that it can be broken down by stomach acid.

Even though ferrous fumarate spends more time in your stomach, it is thought to be the most gentle form of iron to take.

Even with their differences, the truth is that any of these three iron supplements will work just fine. It’s all about which form you tolerate best and making sure you take the amount your doctor has prescribed.

How Should You Take Iron Supplements?

You can affect how well your body absorbs the iron you take by what you eat or drink with your iron supplement.

Iron needs vitamin C to be absorbed properly. Taking your iron supplement with a small glass of orange juice can protect the iron while it’s being transported. This is also helpful if you’re taking a ferric iron supplement, as your body needs vitamin C to turn it into the ferrous form.

Coffee, tea, and anything containing calcium should be avoided with iron supplements. These all reduce your body’s ability to absorb iron.

If you do decide to take your iron supplement with orange juice, watch out for brands that fortify their orange juice with calcium.

It is not recommended to take iron supplements with food, but some doctors will recommend it if you experience nausea or other unpleasant symptoms. Always listen to your doctor’s advice and take the amount that they recommend.

Takeaway Notes

  • Ferrous fumarate, sulfate, and gluconate are all forms of iron supplements.
  • Iron is important for the transport of oxygen through blood and to muscles.
  • Women are at a higher risk for iron deficiencies. This is because women store less iron and lose some when they menstruate.
  • Ferrous sulfate is the form that is easiest for your body to absorb but can cause stomach upset.
  • Ferrous fumarate is the form that is easiest on the stomach but is not as easily absorbed.
  • Take iron with a beverage containing vitamin C to help with absorption.
  • Avoid taking iron supplements with coffee, tea, or beverages containing calcium.
Kelli Yates
Kelli Yates
Kelli Yates is a health and nutrition writer, dietetics student, and co-host and creator of The Nutrition Nerds Podcast. In her spare time she teaches the free class Well-Fed Survival: Eating Healthy After A Disaster, which helps people build nutritious emergency food supplies and prepare for natural disasters.
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