Iron deficiency anemia is one of the most common nutrient deficiencies worldwide. Iron is essential for forming red blood cells and delivering oxygen throughout the body. Anemia occurs when there are not enough healthy red blood cells in the body.

Iron supplements help increase iron levels in the body, especially when getting iron through diet alone isn’t enough. All iron supplements treat anemia, but their absorption rates and side effects vary.

How Do Iron Supplements Help Anemia?

Iron supplements help increase the amount of iron and hemoglobin in your body when consuming iron-rich food isn’t enough. This helps treat and resolve the symptoms of iron deficiency anemia.

Iron deficiency anemia results from low hemoglobin levels. Hemoglobin is a red blood cell protein that holds iron and delivers oxygen from the lungs to tissues in the body.

Anemia affects mood, cognition, energy levels, and countless other bodily activities. Symptoms of mild anemia include the following:

• Fatigue
• Irritability
• Loss of appetite
• Headaches or trouble concentrating or thinking
• Numbness or tingling of the extremities

Symptoms become more severe as anemia worsens. Symptoms of more severe anemia include the following:

• Brittle nails
• Lightheadedness with standing
• Shortness of breath
• Sore or inflamed tongue; mouth ulcers
• Desire to eat ice or other nonfood items (pica)

How Long Do Iron Supplements Take to Work?

Generally, it takes two months of iron supplementation for serum levels to return to normal. However, continued supplementation may be recommended to build up your body’s iron stores.

That said, how long you will need to take iron supplements depends on the severity of your anemia, the supplement form, and how you take it.

A blood test after eight to 12 weeks of supplementation helps you and your healthcare provider monitor changes in iron levels. Even when iron levels return to normal, you may still need to retake supplements in the future.

Prioritizing iron-rich foods and periodically checking iron levels enables you to make better informed decisions about your supplement routine.  

Who Should Consider Supplementation?

Specific factors increase the risk of iron deficiency and may affect its severity. More severe iron deficiency likely requires higher supplement doses.

You lose some of the iron in your body through urine, feces, the digestive system, and skin. However, the following individuals may be at a greater risk of iron deficiency:

• People who menstruate due to blood loss, especially heavy periods (ex., in endometriosis)
• Runners who lose iron from the impact of their soles hitting the ground
• People who are pregnant have increased iron needs and may require higher dosages
• People with cancer (especially colon cancer)
• People with inflammatory bowel disease (IBD)
• People with a history of gastrointestinal surgery
• People who have kidney disease and have trouble making red blood cells

A blood test is required to diagnose anemia. The blood test checks hemoglobin, hematocrit, mean corpuscular volume (MCV) levels, transferrin, and ferritin. Hematocrit reflects the proportion of red blood cells in the blood, and MCV measures red blood cell size. Your blood test may point to iron deficiency anemia if you have:

• Low hemoglobin
• Low hematocrit
• Low MCV
• Low transferrin
• Low ferritin levels

Types of Iron Supplements

Iron supplements are available as capsules, tablets, chewable tablets, and liquids. 

Types of iron supplements for anemia include:

• Ferrous sulfate
• Ferrous gluconate
• Ferrous fumarate
• Ferrous bisglycinate
• Ferric citrate
• Ferric sulfate

Aside from their varying physical forms, their chemical composition also differs. Many supplements are ferrous or ferric iron salts. Iron also attaches to carbohydrates, amino acids, or other minerals to form supplements. Iron carbohydrate supplements are in the ferric form.

Choosing the Right Supplement for You

Considerations when choosing a supplement include the following:

• Elemental iron (the amount of iron the body absorbs from a supplement): The amount of elemental iron in a supplement varies depending on the form. For example, ferrous sulfate contains roughly 20% elemental iron compared to ferrous fumarate, which is 33% elemental iron. Look on your label’s supplement facts panel to see the amount of elemental iron in the supplement.
• Different iron forms: Ferrous iron dissolves easier than ferric iron, so the body absorbs it and uses it more easily. Ferric iron requires acidity for absorption. Iron carbohydrate supplements are in the ferric form. They may be more palatable but are less bioavailable and require a longer supplement duration.
• Vegetarian- or vegan-friendly options: The iron in iron supplements is chemically formulated and not specifically heme (from animal sources) or non-heme (from plant sources). Therefore, iron supplements are vegetarian- and vegan-friendly. However, some iron supplements may contain other ingredients that are not vegetarian- or vegan-friendly, such as gelatin. 

Potential Side Effects

Potential Side Effects

Possible side effects of iron supplements include the following:

• Abdominal pain and cramping
• Upset stomach
• Diarrhea
• Constipation
• Black stools 

The severity of side effects depends on the supplement dosage, form of iron, and other factors. Higher doses may cause nausea and vomiting.

You can minimize certain side effects by:

• Taking smaller doses throughout the day to reduce nausea.
• Taking your supplement with food to reduce gastrointestinal effects. However, this may also interfere with absorption.
• Mixing iron with other liquids or brushing your teeth with baking soda to reduce teeth staining caused by liquid iron.
• Choosing a supplement that is gentler on the gastrointestinal tract. Chelated iron supplements bound to an amino acid like iron bisglycinate may cause fewer side effects than iron salts. Opt for a ferrous iron form instead of a ferric iron one to minimize side effects.   

Long-Term Effects

Achieving sufficient iron levels is vital for health. However, too much iron can be toxic to your body.

Additionally, long-term supplementation can impact your bowel function. Chronic constipation contributes to bloating and may affect appetite. Difficulty with bowel movements, such as straining, pain, or even bleeding, can lead to hemorrhoids. Persistent diarrhea affects electrolyte levels.

How to Maximize the Benefits of Iron Supplements

Optimize Dosage

Tips for maximizing the absorption of iron supplements include:

• Take it on an empty stomach: Your body absorbs iron best on an empty stomach Taking iron on an empty stomach one hour before or two hours after a meal helps with absorption.
• Take it in the morning: Some research suggests the best time of day to take iron supplements is the morning. Taking it in the morning increases hepcidin levels, which may aid absorption. Hepcidin is the primary regulator of iron absorption.
• Talk to your healthcare provider about your dosing schedule: Some research suggests that multiple dosages per day may improve iron levels faster than once daily or alternate-day supplementation. Additionally, other research suggests that taking high-dose iron supplements on alternate days may be more effective and beneficial for improving nutrient stores. Still, follow your healthcare provider’s guidelines regarding single, multiple, or alternate-day dosing.
• Pair your supplement with a source of ascorbic acid (vitamin C): For optimal absorption, include a vitamin C-rich drink alongside your supplement. For example, pair an iron supplement with an 8-ounce (oz) glass of orange juice, which contains roughly 84 milligrams (mg) of vitamin C.
• Be consistent: Pick a time of day that works best for you and try to be consistent when taking the iron supplement. 

You should not stop taking iron supplements even once your symptoms improve. Only discontinue if your healthcare provider recommends it. Periodic blood work and consultations with your healthcare provider will indicate whether you need to stop taking your iron supplements, increase their dosage, or switch their forms. 

Avoid Interactions

Certain foods inhibit iron absorption, including the following:

• Calcium
• Milk
• Coffee
• Tea
• High-fiber foods

Take iron separately from these foods to minimize any adverse effects. Adjust your diet to ensure you’re consuming these foods at least an hour apart from your iron supplement.

Other factors, such as exercise and medication, affect iron absorption. Exercise increases hepcidin levels, so taking iron after exercise may inhibit absorption. 

Medications that interact with iron supplements include the following:

• Penicillin
• Levothyroxine (treats hypothyroidism)
• Levodopa (treats Parkinson’s disease)
• Proton pump inhibitors
• Antacids

Take medication two hours apart from iron supplements.

Iron-Rich Foods vs. Iron Supplements for Anemia

Plant-based and animal foods contain iron. Eating an iron-rich diet may help maintain iron levels, but supplementation is required to resolve deficiencies.

Heme vs. Non-Heme Iron

Two forms of iron exist: heme and non-heme iron. Animal products like meat, fish, and poultry contain a mix of heme and non-heme iron. Approximately 40% of the iron in animal products is heme iron, whereas 60% is non-heme. 

Plant-based foods like fruits, vegetables, beans, nuts, and grains contain only non-heme iron. Plant-based foods like legumes (beans and lentils), nuts, seeds, and leafy greens contain non-heme iron.  

Iron Absorption From Food

The body absorbs heme iron more easily. Still, iron has a low absorption rate from food. The amount of iron absorbed from foods is roughly the following:

• Dried beans: 2%
• Grains: 4%
• Leafy green vegetables: 7% to 9%
• Organ meats: 25% to 30%

However, people who follow specific diets may need to avoid meats.

Cooking Methods to Boost Iron

Cooking with cast iron pans adds non-heme iron to foods. Consider cooking red meat in a cast iron pan to boost iron content. Vegetarians and vegans should cook iron-rich legumes or leafy greens in a cast iron pan with vitamin C-rich foods like citrus to augment iron content and make it more bioavailable.

The Importance of Food and Supplements

Food may not always be the best way to resolve anemia because of its low absorption rate. Supplements supplement the diet, providing additional nutrients to support health. Prioritizing an iron-rich diet alongside an iron supplement may be most effective for increasing nutrient stores and resolving deficiency. 

Always defer to your healthcare provider about iron supplementation.

Summary

Supplements for anemia resolve iron deficiencies, improving health and physical functioning. Multiple iron supplements exist, but some are more effective and gentler on the body. 

Depending on your anemia’s severity, your healthcare provider will recommend a specific iron dosage to resolve it. To maximize absorption and effectiveness, take iron supplements on an empty stomach with a glass of orange juice unless your healthcare provider or pharmacist suggests you avoid orange juice. Although some evidence suggests consuming iron in the morning may be optimal, regularly and consistently taking your supplement is what matters most.