Iron Supplement Comparison Tool
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Comparison Table
| Form | Elemental Iron % | Daily Dose (mg) | Absorption | GI Side-effects | Cost (£/month) |
|---|---|---|---|---|---|
| Ferrous sulfate | 20% | 100-200 | High | Moderate-high | £3-£5 |
| Ferrous gluconate | 12% | 100-200 | Moderate | Low | £5-£7 |
| Ferrous fumarate | 33% | 100-200 | High | Moderate | £4-£6 |
| Carbonyl iron | 20% | 100-200 | Moderate | Very low | £6-£9 |
| Iron polysaccharide | 20% | 60-120 | Very high | Very low | £8-£12 |
| Iron bisglycinate | 20% | 30-60 | Very high | Very low | £10-£15 |
When you need a boost of iron, the shelves are crowded with names like Ferrous sulfate is a widely used iron salt that delivers a high dose of elemental iron per tablet. But is it the right choice for you? This guide compares ferrous sulfate with the most common alternatives, breaks down how they differ in absorption, side‑effects, cost, and helps you pick the supplement that matches your health goals.
Quick Take
- Ferrous sulfate offers the highest elemental iron (around 20% by weight) but can cause stomach upset.
- Ferrous gluconate is gentler on the gut, supplies less iron per pill, and is good for chronic users.
- Ferrous fumarate sits between the two in potency and tolerability.
- Carbonyl iron provides pure elemental iron with minimal gastrointestinal irritation.
- Iron polysaccharide and iron bisglycinate are newer, highly absorbable forms suitable for sensitive stomachs.
What Is Ferrous Sulfate?
Ferrous sulfate is a salt of iron (Fe²⁺) and sulfuric acid. In supplement form it usually appears as ferrous sulfate heptahydrate, delivering about 20mg of elemental iron per 325mg tablet. It’s inexpensive, widely available, and has a long track record for treating iron‑deficiency anemia.
Because the iron is in a simple ionic form, the body can absorb it quickly-provided the stomach is acidic enough. The downside is that the same chemical reactivity can irritate the lining of the stomach and cause constipation, nausea, or dark stools.
Common Alternatives to Ferrous Sulfate
Below are the five most popular iron salts you’ll see on pharmacy shelves.
- Ferrous gluconate: Iron bound to gluconic acid; milder on the stomach, about 12% elemental iron.
- Ferrous fumarate: Iron bound to fumaric acid; 33% elemental iron, decent absorption, moderate side‑effects.
- Carbonyl iron: Microparticulate elemental iron; virtually no gastrointestinal irritation, about 20% elemental iron.
- Iron polysaccharide (e.g., ferric maltol): Iron complexed with a carbohydrate matrix; high bioavailability and low discomfort.
- Iron bisglycinate: Iron chelated with two glycine molecules; excellent absorption and minimal side‑effects.
Each form changes how much iron you actually get per pill and how your gut reacts.
How the Supplements Differ
| Form | Elemental Iron % | Typical Daily Dose (mg elemental) | Absorption (relative) | GI Side‑effects | Cost (UK £ per month) |
|---|---|---|---|---|---|
| Ferrous sulfate | 20% | 100-200mg | High | Moderate‑to‑high | £3-£5 |
| Ferrous gluconate | 12% | 100-200mg | Moderate | Low | £5-£7 |
| Ferrous fumarate | 33% | 100-200mg | High | Moderate | £4-£6 |
| Carbonyl iron | 20% | 100-200mg | Moderate | Very low | £6-£9 |
| Iron polysaccharide | 20% | 60-120mg | Very high | Very low | £8-£12 |
| Iron bisglycinate | 20% | 30-60mg | Very high | Very low | £10-£15 |
The numbers above are averages from UK NHS formularies, product labels, and clinical studies published up to 2024.
Choosing the Right Iron Supplement
Think of the decision as matching three pieces: how much iron you need, how your stomach reacts, and your budget.
- Severity of deficiency. If blood tests show severe anemia (hemoglobin<10g/dL) you may need the highest elemental iron-ferrous sulfate or ferrous fumarate.
- Tolerance. If you experience nausea, constipation, or black stools with ferrous sulfate, switch to a gentler form like carbonyl iron or iron bisglycinate.
- Frequency of dosing. Some forms (polysaccharide, bisglycinate) are effective at lower doses taken once daily, which can simplify routines.
- Cost considerations. Generic ferrous sulfate remains the cheapest option, but the price gap has narrowed as newer formulations become more common in UK pharmacies.
Here’s a quick rule‑of‑thumb:
- First‑line, short‑term therapy for most adults: Ferrous sulfate (unless you’ve already had GI trouble).
- Long‑term maintenance or sensitive stomachs: Carbonyl iron or Iron bisglycinate.
- Budget‑tight patients who can tolerate mild side‑effects: Ferrous gluconate or Ferrous fumarate.
Practical Tips for Maximizing Iron Absorption
- Take your supplement on an empty stomach with a full glass of water, unless it upsets you.
- VitaminC boosts absorption-drink orange juice or chew a vitaminC tablet 30minutes before or after the iron dose.
- Avoid calcium‑rich foods, tea, coffee, or antacids within two hours of taking iron, as they hinder uptake.
- Check your lab results after 4-6weeks; adjust dose based on hemoglobin and ferritin trends.
- If you’re pregnant, consult your GP-iron needs rise to about 30mg elemental iron daily.
Mini‑FAQ
Can I switch from ferrous sulfate to another iron supplement without a doctor’s note?
Most healthy adults can change over‑the‑counter iron types on their own, but if you’ve been diagnosed with anemia, it’s wise to let your GP know. They can retest your blood levels after a few weeks to make sure the new form is working.
Why do iron pills turn my stool black?
Unabsorbed iron reacts with digestive enzymes and bacteria, forming ferric sulfide-a black compound. It’s harmless, but if you notice blood‑red stool, contact a doctor.
Is iron polysaccharide better than ferrous sulfate for vegetarians?
Yes, because it’s highly absorbable and doesn’t rely on meat‑derived heme iron. Vegetarians often benefit from the gentler gut profile of polysaccharide or bisglycinate forms.
How long should I stay on an iron supplement?
Typically 3-6months after blood levels normalize, then shift to a maintenance dose (often half the therapeutic dose) to keep ferritin stable.
Do iron supplements interact with other medications?
Yes. Antibiotics like tetracycline and fluoroquinolones, thyroid meds, and bisphosphonates can bind iron and reduce absorption. Space them at least two hours apart.
Bottom Line
If you need a fast, cost‑effective way to replenish iron stores and can handle a bit of stomach upset, ferrous sulfate remains the go‑to choice. For chronic users, sensitive intestines, or when you’re looking for the highest absorption per milligram, explore carbonyl iron, iron polysaccharide, or iron bisglycinate. Always pair the supplement with vitaminC, monitor your labs, and talk to a healthcare professional if you’re unsure which form fits your lifestyle.
1 Comments
Sharon Lax
October 1, 2025While the article offers a decent overview, it fails to acknowledge the pharmacokinetic nuances that differentiate ferrous sulfate from chelated complexes. The discussion could benefit from integrating bioavailability coefficients and the impact of gastric pH on iron oxidation states.