In this guide, we’ll help you understand the types of iron supplements and what to look for in an iron vitamin.


By Halle Tecco

Iron is a micronutrient vital to disease prevention, health, and wellbeing. Although iron is found naturally in many foods, it is difficult for your body to absorb, especially during pregnancy. Without enough iron, your body cannot make hemoglobin, and you may develop anemia. Anemia is the most common blood disorder, and according to the National Heart, Lung, and Blood Institute, it affects more than three million Americans. 

According to the Centers for Disease Control and Prevention (CDC),

  • Iron is critical for motor and cognitive development. Children and pregnant women are especially vulnerable to the consequences of iron deficiency.
  • Iron is a leading cause of anemia which is defined as low hemoglobin concentration. Anemia affects 43% of children younger than five years of age and 38% of pregnant women globally.
  • Anemia during pregnancy increases the risk of death for the mother and low birth weight for the infant. Worldwide, maternal and neonatal deaths total between 2.5 million and 3.4 million each year.
  • The World Health Organization (WHO) recommends iron and folic acid supplements for reducing anemia and improving iron status among women of reproductive age.

One way doctors treat iron deficiency and anemia is through oral iron supplements, intended to increase the levels of iron and hemoglobin in your body. But with so many options on the market, how do you know which type of iron supplement is best for you? 

Look for elemental iron on the “Supplement Facts”

Elemental iron is the form of iron used by your body, and each type of iron has a different percent of elemental iron. Often, two iron amounts are listed on the label: the larger number being the chemical compound form and the smaller number being the amount of iron in the compound (aka the elemental iron). 

Elemental iron is the more important number because this is the amount available for the body to absorb. When choosing a supplement, look at the amount of elemental iron in the formula (it may differ from the total amount of iron). For instance, 

  • Carbonyl has 98-100% elemental iron
  • Ferrous fumarate has approximately 33% elemental iron
  • Ferrous sulfate has 20% elemental iron
  • Ferrous gluconate has 12% elemental iron

Read the label closely. For example, 54 mg of carbonyl contains 54 mg of elemental iron, but 54 mg of ferrous sulfate contains only 10.8 mg of elemental iron.

Look for Carbonyl iron 

Not only does Carbonyl iron contain the most elemental iron, it is often preferred by physicians because it is less toxic to children who might take an accidental overdose. Carbonyl iron is significantly less toxic than the other options due to the fact that it must first be solubilized by gastric acid.

One research paper called Carbonyl iron “an effective, inexpensive treatment for iron deficiency anemia” because it is “accompanied by tolerable side effects and may have an advantage over therapy with iron salts by substantially reducing or eliminating the risk of iron poisoning in children.”

Look for an iron supplement that is slow-release 

If you’re pregnant, a slow-release tablet is the best choice. Research shows that controlled-release iron causes less nausea and constipation and is also better tolerated. Three large randomized trials assessed tolerability of controlled-release iron compared to quick-release. The double blinded study found a lower rate of nausea and epigastric pain in the controlled-release iron formulation among 1,376 blood donors receiving 200 mg of elemental iron every day. 

💊 Shop Slow-release Iron

Decide if you prefer a tablet or liquid

Iron supplements generally come in liquid, tablet, or capsule form. We haven’t found a manufacturer that makes iron gummies, probably due to the unpleasant taste of iron alone (or the fact that gummies look like candy to children). Gummy multivitamins are also more likely to fail ConsumerLab's tests of quality than tablets, as they often contain much less or much more of the listed amounts of ingredients.

If you have difficulty swallowing pills, then liquid may be a good alternative. However, liquid is often harder on the stomach, so there’s a tradeoff. The Natalist Iron supplement is a small tablet, which has low toxicity and is easy on the stomach. 

Choose a brand that is GMP certified

GMP (which stands for 'Good Manufacturing Practices') is a set of best practices for dietary supplement manufacturing in the United States that are maintained by the FDA. These regulations establish the baseline quality requirements for dietary supplement companies and manufacturers. In addition to ensuring quality control and assurance, GMP’s requirements help ensure that dietary supplement products consistently meet specifications for purity, strength, and composition. Manufacturers get GMP certified through an audit by a third-party organization like NSF. If you don’t see GMP or NSF certification, R-U-N. 

All Natalist vitamins are made in an NSF-certified facility, which exceeds the FDA cGMP (Good Manufacturing Practices) manufacturing standards. Certificates of analysis are reported for every batch of manufactured vitamin to ensure final product integrity and quality. 

Ask your physician for the right dosage

Too much iron can be toxic to the liver and cause serious health problems. The best way to determine your optimal dose is to talk to your doctor and take an iron supplement as instructed. For pregnant women, the CDC recommends treating anemia through an oral dose of 60 to 120 mg per day of iron. Always check with your physician before starting an iron supplement, and be sure to get a specific recommendation for the type of iron and dosage.

Learn more about proper nutrition for fertility and pregnancy.