Quick Summary
- Three factors matter when choosing iron: absorption pathway, elemental iron content, and tolerability profile.
- Elemental iron content varies by form — 325 mg ferrous sulfate contains only 65 mg elemental iron.
- Bisglycinate's dual-pathway absorption (DMT1 + PepT1) means effective doses at lower elemental iron.
- The best iron supplement is the one you'll actually take consistently — tolerability drives compliance.
Choosing an iron supplement comes down to three pharmacokinetic questions: (1) Does the iron form minimise colonic free-iron exposure? (2) Is the elemental iron dose within the DMT1 absorption window? (3) Does the formulation account for hepcidin timing?
If you understand these three factors, you can evaluate any iron supplement on the market — regardless of branding.
Why iron form matters more than iron dose
Iron supplements fail for one reason: more iron enters the colon than the duodenum can absorb. The unabsorbed fraction catalyses the Fenton reaction — free Fe²⁺ reacts with hydrogen peroxide to produce hydroxyl radicals (OH·), the most reactive oxygen species in biology.
These radicals damage the colonic mucosa, disrupt the gut microbiota (shifting populations away from Lactobacillus and Bifidobacterium toward pathogenic Enterobacteriaceae), and trigger the nausea, cramping, and constipation that cause 30–50% of patients to discontinue iron therapy (Tolkien et al. 2015).
The solution is not "less iron." It is more efficient absorption per milligram — so less iron reaches the colon in the first place.
Two absorption pathways: DMT1 vs PepT1
Traditional iron salts (ferrous sulfate, fumarate, gluconate) dissociate in gastric acid to release free Fe²⁺ ions. These ions are absorbed exclusively through the DMT1 transporter (divalent metal transporter 1) on the apical membrane of duodenal enterocytes.
DMT1 is saturable. It handles a fixed throughput of Fe²⁺ per unit time. When the dose exceeds DMT1 capacity, the excess free iron transits to the colon unabsorbed.
The chelation advantage: Ferrous bisglycinate keeps iron bonded to two glycine molecules through gastric transit. This intact chelate can be absorbed via the PepT1 peptide transporter — which treats the chelated complex as a dipeptide. Dual-pathway access (DMT1 + PepT1) means more iron is absorbed before DMT1 saturates, reducing the fraction that spills into the colon (Pineda & Ashmead 2001).
Elemental iron: the number that actually matters
Supplement labels show compound weight (e.g., "325 mg ferrous sulfate"), but absorption depends on elemental iron content — the actual absorbable iron fraction:
| Iron Form | Compound Weight | Elemental Iron | % Elemental |
|---|---|---|---|
| Ferrous sulfate | 325 mg | ~65 mg | ~20% |
| Ferrous fumarate | 200 mg | ~66 mg | ~33% |
| Ferrous gluconate | 300 mg | ~35 mg | ~12% |
| Ferrous bisglycinate | Varies | 25–36 mg typical | ~20% |
The critical insight: a 65 mg elemental dose from sulfate at ~10% bioavailability delivers ~6.5 mg to the bloodstream — but dumps ~58 mg into the colon as free Fe²⁺. A 36 mg dose from bisglycinate at ~30% bioavailability delivers ~11 mg — with only ~25 mg reaching the colon, mostly as intact chelate rather than free ions.
Lower elemental dose + higher bioavailability = more iron absorbed, less iron causing damage.
The hepcidin timing window
Even with the right form and dose, when you take iron matters. Hepcidin — the liver-produced peptide hormone that regulates iron absorption — rises 6–8 hours after an iron dose and stays elevated for ~24 hours (Moretti et al. 2015).
During this window, hepcidin binds ferroportin on enterocytes, blocking iron export to the bloodstream. A second dose taken within this window encounters a partially closed gate — absorption drops to 35–45% of the first dose's efficiency (Stoffel et al. 2017).
Practical implication: Once-daily dosing is pharmacokinetically superior to split dosing. Alternate-day dosing allows full hepcidin reset and has shown comparable haemoglobin outcomes in clinical trials. The iron form should be efficient enough to deliver adequate iron in a single moderate dose.
A pharmacokinetic checklist for choosing iron
Based on the mechanisms above, evaluate any iron supplement against these criteria:
- Iron form: Does it access PepT1 (chelated) or only DMT1 (ionic salt)? Dual-pathway = less colonic spillover
- Elemental dose: Is it 25–36 mg (the absorption sweet spot) or 65+ mg (beyond DMT1 capacity)?
- Vitamin C inclusion: Does it include ascorbic acid to enhance Fe³⁺→Fe²⁺ reduction at the enterocyte surface?
- Dosing frequency: Once daily or alternate-day? Split dosing wastes the second dose against elevated hepcidin
- Cofactors: Does it include B12 (Methylcobalamin), Folate (5-MTHF), and B6 (P5P) for downstream erythropoiesis?
How Hemascore applies this framework
Hemascore was designed around these pharmacokinetic principles:
- 36 mg elemental iron from ferrous bisglycinate — dual DMT1/PepT1 absorption, within the saturation-avoidance window
- Vitamin C included — enhances Fe³⁺→Fe²⁺ reduction at the enterocyte brush border
- Active B-vitamin cofactors: P5P (B6), Methylcobalamin (B12), 5-MTHF (Folate) — supporting erythropoiesis downstream of iron absorption
- Once-daily after food — aligned with hepcidin timing for maximal ferroportin availability
To see the full ingredient list, visit the Hemascore product page.