Carbonyl Iron
Also known as: Carbonyl iron, Carbonyl iron powder, Elemental iron, Carbonyl Iron
Overview
Carbonyl iron is a highly pure, synthetic form of elemental iron produced industrially by the thermal decomposition of iron pentacarbonyl. It is primarily used as an oral iron supplement to treat and prevent iron deficiency anemia and to replenish iron stores. Characterized by its high purity (>97%), small particle size, and slow absorption profile, carbonyl iron is considered to have lower gastrointestinal (GI) toxicity compared to other iron forms like ferrous salts. While multiple clinical trials exist, large-scale systematic reviews focusing exclusively on carbonyl iron are less common than for other iron supplements. Evidence includes randomized controlled trials comparing it to other iron supplements, with some meta-analyses on oral iron therapies in general.
Benefits
Carbonyl iron effectively increases hemoglobin and ferritin levels, thereby improving iron status in individuals with iron deficiency. A randomized controlled trial demonstrated that modified-release (MR) carbonyl iron was more efficacious than ferrous fumarate in correcting hematologic abnormalities in nutritional iron deficiency anemia, showing statistically significant improvements in hemoglobin and iron parameters. This indicates its clinical relevance. Carbonyl iron is also associated with fewer gastrointestinal side effects, such as constipation, nausea, or abdominal discomfort, compared to ferrous sulfate and other ferrous salts, likely due to its slower absorption and reduced free iron release in the gut. It is particularly effective in adults with nutritional iron deficiency anemia, with improvements in iron status typically observed over weeks to months of consistent supplementation.
How it works
Carbonyl iron provides elemental iron that is absorbed primarily in the duodenum and upper jejunum after it slowly dissolves. Once absorbed, this iron is incorporated into hemoglobin for oxygen transport and into ferritin for storage. The iron supports erythropoiesis by supplying the necessary component for hemoglobin synthesis and replenishes iron stores in the liver and bone marrow. Its absorption is facilitated by iron transporters like divalent metal transporter 1 (DMT1). The slower dissolution and absorption rate of carbonyl iron, compared to ferrous salts, results in a more gradual release of iron into the system, which is believed to contribute to its lower incidence of gastrointestinal side effects.
Side effects
Carbonyl iron is generally safe and well-tolerated at recommended doses, with a lower incidence of gastrointestinal adverse effects compared to ferrous sulfate. Common side effects, occurring in more than 5% of users, are mild gastrointestinal symptoms such as constipation, nausea, or abdominal discomfort, though these are less frequent than with ferrous sulfate. Uncommon side effects (1-5%) rarely include allergic reactions or iron overload if taken inappropriately. Severe hypersensitivity or iron toxicity are rare (<1%) but can occur, especially in cases of overdose. Carbonyl iron may interact with antacids, tetracyclines, and other drugs that affect iron absorption. It is contraindicated in individuals with hemochromatosis, hemosiderosis, or other iron overload disorders. Caution is advised when used in children due to the risk of overdose, and medical supervision is recommended during pregnancy and lactation.
Dosage
The minimum effective dose of carbonyl iron typically ranges from 50-100 mg of elemental iron daily, depending on the severity of the iron deficiency. Optimal dosage ranges from 50-200 mg elemental iron per day; modified-release formulations may allow for convenient once-daily dosing. Doses exceeding 200 mg elemental iron daily should be avoided without medical supervision due to the increased risk of toxicity. While best absorbed on an empty stomach, carbonyl iron may be taken with food to minimize gastrointestinal side effects, though absorption might be slightly reduced. Co-administration with Vitamin C can enhance absorption, but concurrent intake with calcium or antacids should be avoided as they can interfere with iron absorption.
FAQs
Is carbonyl iron safer than ferrous sulfate?
Yes, carbonyl iron generally causes fewer gastrointestinal side effects due to its slower absorption and lower free iron release in the gut, making it better tolerated.
How long until results are seen?
Improvements in hemoglobin levels are typically observed within 4-8 weeks, but full replenishment of iron stores may take longer, often several months.
Can it be taken with food?
Yes, it can be taken with food to reduce potential gastrointestinal upset, although absorption might be slightly decreased compared to taking it on an empty stomach.
Is it effective for all types of anemia?
No, carbonyl iron is primarily effective for iron deficiency anemia. It will not be effective for anemias caused by other underlying conditions.
Research Sources
- https://www.semanticscholar.org/paper/Comparative-assessment-of-the-bioavailability,-and-Adsul-Desai/cbb234ae7f5f6417516d186816b8bdb68cec82b4 – This randomized controlled trial (RCT) compared modified-release (MR) carbonyl iron with ferrous fumarate in patients with nutritional iron deficiency anemia. The study found that MR carbonyl iron was more efficacious in improving hematologic parameters and iron status, and also demonstrated better tolerability. This suggests carbonyl iron is an effective and well-tolerated option for iron deficiency.
- https://onlinelibrary.wiley.com/doi/full/10.1002/ejhf.514 – This Cochrane systematic review and meta-analysis evaluated various iron therapies, including oral and intravenous forms, for iron deficiency. While it confirmed that iron therapies improve hemoglobin levels, it noted no mortality benefit and highlighted the acceptable safety profile. However, it did not specifically focus on carbonyl iron, and direct data for this specific form within the review were limited.
- https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0117383 – This meta-analysis of randomized controlled trials primarily focused on ferrous sulfate and its association with gastrointestinal side effects. While carbonyl iron was not directly studied, the findings indirectly support the notion that iron forms with slower absorption, like carbonyl iron, would have a better safety profile due to reduced immediate free iron release in the gut.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10331582/ – This source provides general information on carbonyl iron, confirming its nature as a highly pure elemental iron and its use as an oral iron supplement. It supports the understanding of carbonyl iron's characteristics, such as its high purity and slow absorption, which contribute to its efficacy and reduced gastrointestinal side effects compared to other iron forms.
- https://www.who.int/tools/elena/review-summaries/daily-iron-women--daily-iron-supplementation-for-improving-anaemia-iron-status-and-health-in-menstruating-women – This WHO review summary discusses daily iron supplementation for improving anemia and iron status, particularly in menstruating women. While not specific to carbonyl iron, it provides context on the broader efficacy of oral iron therapies in vulnerable populations, supporting the general benefit of iron supplementation for iron deficiency.
Supplements Containing Carbonyl Iron
Corvite FE
Vertical Pharmaceuticals
Bump DHA
Centurion
OB Complete Petite
Vertical Pharmaceuticals
OB Complete Premier
Vertical Pharmaceuticals
Extra Strength
Focus Factor
Bariatric Advantage. Chewable Iron 18 mg with Vitamin C
Bariatric Advantage®
Vitron-C High Potency Iron plus vitamin C
Vitron-C
Women's Multi with Added Whole Foods
FarmHaven®
Iron Strong with Vitamin C
Renzo's®
Iron Strong with Vitamin C | Vegan
Renzo's®
Beets Iron
NEVISS®
Iron Boost
Clinicians®