Solgar vs Thorne Iron Bisglycinate 25 mg (2026)
Solgar Gentle Iron (Iron Bisglycinate) 25 mg and Thorne Iron Bisglycinate 25 mg deliver the same 25 mg of elemental iron as bisglycinate in a single capsule, the chelated form chosen specifically because it is gentler on the stomach than ferrous sulfate. The gap is the listing: Thorne lists NSF Certified for Sport (we did not find it in a public registry); Solgar lists no third-party certification. Solgar costs less per day; Thorne costs more for the listed certification.
Informational comparison of label data and cost, not medical advice. Prices are per-serving figures as checked on the date shown below; formulas are each brand’s published Supplement Facts.
The numbers, side by side
| Solgar Gentle Iron (Iron Bisglycinate) 25 mg | Thorne Iron Bisglycinate 25 mg | |
|---|---|---|
| Form | Iron bisglycinate (chelated) | Iron bisglycinate (chelated) |
| Dose / serving | 25 mg | 25 mg |
| Serving size | 1 capsule | 1 capsule |
| Servings / container | 90 | 60 |
| Third-party cert | None | NSF Certified for Sport |
| Public registry | not found | NSF Certified for Sport, listing #1205059 (read 2026-10-01) |
| Price | $9.65 | $16.00 |
| Cost / day | $0.11 | $0.27 |
| Buy | Check price → | Check price → |
Prices are Amazon figures ÷ pack serving count, as checked 2026-10-05. Formula details are each brand’s published Supplement Facts panel.
The real difference
Both products use iron bisglycinate, a chelate in which iron is bound to two glycine molecules. That chelation is the whole point of the form: it is the reason bisglycinate is tolerated by people who cannot take ferrous sulfate without constipation or nausea. Both land at 25 mg of elemental iron per capsule, so the active ingredient and the dose are the same.
What separates them is the certification: Thorne is in the NSF Certified for Sport registry (listing #1205059, the 60-capsule bottle), and Solgar lists no certification. A certification would not change the iron itself.
25 mg against the reference intakes
The NIH Office of Dietary Supplements puts the adult RDA at 8 mg a day for men and for women over 50 and 18 mg for women aged 19 to 50, with a tolerable upper intake level of 45 mg a day for adults from all sources. One capsule of either product therefore covers a menstruating woman’s full RDA with room to spare and sits just over half of the upper level; two capsules a day would exceed it. That is the arithmetic behind the advice to test first and to ask your clinician about any dose.
How you take the capsule changes how much of the 25 mg you keep. In two randomised trials in 40 iron-depleted women, a 60 mg dose of iron given on alternate days was absorbed at 21.8% cumulatively against 16.3% when the same dose was given on consecutive days, because each daily dose raises hepcidin and blunts absorption from the next (Stoffel 2017, PMID 29032957). Those trials used ferrous sulfate, not bisglycinate, so the exact percentages do not transfer, but the hepcidin mechanism does, and it is the reason a 25 mg capsule every other morning is the schedule those studies point to; ask your clinician before choosing one for either of these products.
Timing matters as much as the schedule. Supplemental iron is absorbed best away from meals, and the NIH Office of Dietary Supplements fact sheet notes that calcium can interfere with its absorption, that polyphenols in tea and coffee reduce non-heme iron uptake, and that vitamin C improves it. In practice that means the capsule first thing with water or a glass of orange juice, not with breakfast cereal, milk or a calcium supplement, and not with the morning coffee. Bisglycinate is the form most people can manage on an empty stomach; if it still causes nausea, taking it with a small amount of food loses some absorption but keeps the habit, which over months matters more.
What the NSF listing does and does not tell you
Thorne Iron Bisglycinate is in the NSF Certified for Sport registry (listing #1205059, 60 capsules, read 2026-10-01), and Solgar states no third-party certification on the label. NSF Certified for Sport means the finished product is tested against its label and screened for substances banned in sport. It would not change the iron: the bisglycinate chelate, the 25 mg dose and the single-capsule serving are the same in both products, and no certification programme measures how well a person absorbs or tolerates a product.
The cost of the listing, at the prices we checked, is $0.16 a day or about $58 a year against Solgar; at one capsule a day Thorne runs $99 a year. The best iron bisglycinate page ranks every buyable product on the same three columns.
Who each one is for
Choose Solgar if you do not need a certification mark. It is the same 25 mg chelated bisglycinate for less per day.
Choose Thorne if an NSF Certified for Sport listing matters to you. It is in the NSF registry (listing #1205059).
Before either iron is the one supplement worth testing before taking. Excess iron accumulates and is genuinely harmful. Ask for ferritin and transferrin saturation rather than supplementing on suspicion.
Our picks
25 mg chelated iron bisglycinate, no third-party certification. $0.11/day.
Same 25 mg bisglycinate; the listing says NSF Certified for Sport. $0.27/day.
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Frequently asked questions
Is Solgar or Thorne iron bisglycinate better?
Same active ingredient and dose: 25 mg of elemental iron as chelated bisglycinate in one capsule. Thorne is in the NSF Certified for Sport registry (listing #1205059, the 60-capsule bottle); Solgar does not list a third-party certification. Solgar costs less per day. If you are drug-tested for sport, check the lot on your bottle at nsfsport.com.
Why is iron bisglycinate gentler than ferrous sulfate?
Bisglycinate binds iron to two glycine molecules, which keeps more of it chelated through the gut rather than free. Free iron is what drives the constipation, cramping and nausea that make ferrous sulfate hard to tolerate. Both products here use the bisglycinate form.
Should I take iron without a blood test?
Generally no. Unlike most nutrients the body has no active route to excrete excess iron, so it accumulates. Supplementing without confirmed deficiency risks overload, and the symptoms people self-treat as low iron often are not. Ferritin plus transferrin saturation is the standard pair of tests.
Related
- Best iron bisglycinate: whole dose per capsule, verification, cost
- Ferrous sulfate vs bisglycinate: why the form changes tolerability
- Iron dosage guide: RDA and timing
- All iron bisglycinate products: ranked by cost per dose
Sources
- NIH Office of Dietary Supplements. “Iron: Health Professional Fact Sheet.” ods.od.nih.gov
- NSF. “Certified for Sport”: what the programme tests. nsfsport.com
- Stoffel NU, et al. “Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials.” Lancet Haematol. 2017. PMID: 29032957
- Product labels and Amazon pricing for both products, as checked 2026-10-05.