Ferrous Gluconate vs. Ferrous Sulfate: What’s the Difference?

If your doctor has prescribed oral iron supplements to treat iron deficiency anemia, you will find different types of supplements available. In this article, we will compare two types of oral iron supplementation—ferrous sulfate and ferrous gluconate.

What is iron deficiency anemia (IDA)?

Iron deficiency anemia is the most common nutritional deficiency worldwide. This condition, which affects 4-5 million Americans, is characterized by not having enough red blood cells in your blood due to low levels of available iron. Red blood cells are needed to carry oxygen to the various tissues in the body. As the name suggests, iron deficiency anemia occurs when there is a deficiency of iron (ferrous) in the body. Iron is necessary for the body to make hemoglobin, which is the substance that carries oxygen.

Causes of Less Elemental Iron in the Body

Iron deficiency anemia can occur due to excessive blood loss, a lack of sufficient iron in your diet, or digestive conditions like inflammatory bowel disease that reduce the body’s ability to absorb iron from food. People on kidney dialysis and pregnant women are at higher risk of iron deficiency.

Symptoms of Iron Deficiency

Symptoms of iron deficiency anemia include fatigue, weakness, pale skin, fast heartbeat, headaches, dizziness, sensitivity to cold, hair loss, brittle nails, and unusual food cravings.

Recommended Daily Amount of Iron

The recommended intake of iron for adults is 18 mg daily for women, 8 mg daily for men, 27 mg daily in pregnant women, and 9 mg daily in lactating women.

There are two forms of iron found in food sources—heme iron in foods from animal sources and non-heme iron in foods from plant sources. If you are a vegetarian and do not get heme iron from meats, you are at risk of developing an iron deficiency. It’s important for you to include enough non-heme iron foods in your diet. Keep in mind that non-heme iron is less well-absorbed and you need to consume bigger quantities of these foods.

Note: Too much iron can be harmful. You should limit intake of iron from dietary sources and supplements to 45 mg daily for men and women aged 14 years and above and 40 mg daily for younger individuals to avoid complications related to excessive iron. Remember that iron is present as a food additive in many foods like cereals.

Treatment for Iron Deficiency

Your doctor may recommend taking an iron supplement to treat or prevent iron deficiency anemia. Iron supplements are available as different types of ferrous salts. While the ferric iron in supplements essentially serves the same function, there are subtle differences between the different iron salts such as ferrous gluconate and ferrous sulfate.

How to read iron supplement labels?

If you have iron deficiency anemia and are taking iron supplements to get enough iron, you will notice that there are two amounts indicated on the label. The bigger number is the compound form of iron bound to a salt, for example, ferrous sulphate or ferrous gluconate. The smaller number is the actual quantity of elemental iron in the supplement. For example, a 325 mg tablet of ferrous sulfate contains 65 mg of elemental iron.

It’s important to check the smaller number, which indicates the quantity of elemental iron in an iron supplement. This is the iron that will be available to your body.

When your physician writes a prescription for iron supplements, ask them to specify whether they mean iron salt or elemental iron to ensure you are taking the correct dose.

What is the difference between gluconate and sulfate?

The main difference between ferrous sulfate and ferrous gluconate—the two forms of ionic compound present in iron supplements—is in the percentage of elemental iron they contain.

Ferrous sulfate contains 20% elemental iron by weight.
Ferrous gluconate contains 12% elemental iron by weight.

Ferrous sulfate is commonly available as a 325 mg tablet. The 325 mg refers to the ferrous sulfate compound. The actual amount of elemental iron in the tablet is 65 mg (this is indicated on the label). In contrast, a 240 mg ferrous gluconate tablet contains 27 mg of elemental iron.

When comparing iron supplements, ferrous gluconate vs. ferrous sulfate, be sure to read the drug label and check how much elemental iron it contains. You would need to take approximately two and a half tablets of a 240 mg ferrous gluconate supplement to get the same amount of elemental iron as one tablet of a 325 mg ferrous sulfate supplement.

Other forms (compounds) of iron supplements are also available, such as ferrous fumarate and ferrous ascorbate.

What is better ferrous sulfate or ferrous gluconate?

Both ferrous sulfate and ferrous gluconate are equally safe, well tolerated, and effective when used at equal doses of elemental iron. Again, whatever iron products you take, make sure you are getting the correct dose of elemental iron.

Is ferrous gluconate easier on the stomach than ferrous sulfate?

Iron supplements can cause gastrointestinal side effects like nausea, vomiting, and abdominal pain. In general, ferrous gluconate tends to be easier on the stomach because it contains less elemental iron.

If you are having trouble tolerating ferrous sulfate, talk to your doctor about taking ferrous gluconate instead and dosing it 2-3 times daily to get the correct dose of supplemental iron.

Newer slow-release formulations of iron supplements are available. They cause fewer gastrointestinal side effects, but contain less iron and are generally more expensive.

Which form of ferrous is best absorbed?

Studies have found that the liquid form of ferrous gluconate is better absorbed than the tablet form of ferrous sulfate. Again, remember that compared to ferrous sulfate, ferrous gluconate has less elemental iron. Therefore, you need to take a bigger dose of ferrous gluconate to correct iron deficiency. Also, ferrous gluconate supplements tend to cost more than ferrous sulfate.

How to take iron supplements?

If your doctor has recommended taking iron supplements to replenish iron reserves and get your blood levels up, it’s important to take the correct dose. You can improve iron absorption by:

Taking iron tablets on an empty stomach. However, if the iron tablets cause upset stomach, you may need to take them with food.
Taking iron tablets with vitamin C, which improves the absorption of iron. The vitamin C can be in the form of a glass of orange juice or a supplement.
Not taking iron with antacids, calcium-rich foods, or calcium supplements. These substances can interfere with iron absorption. Make sure you take your iron supplements two hours before or four hours after antacids and calcium supplements.

Keep in mind that an iron deficiency will not be corrected in a few days or even weeks. Most people need to take iron supplements for several months, perhaps even a year or longer, to restore iron stores. However, you should start to feel better after about one week of treatment. Check with your doctor when to have a blood test to measure iron levels. It is important to look for the cause of the iron deficiency in order to make the correct indication of iron supplementation.

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