01Iron Forms at a Glance
| Form | Elemental Iron | Tolerance | Notes |
|---|---|---|---|
| Ferrous sulfate | High (~20%) | Harshest — nausea, constipation common | Cheapest; the standard prescription form |
| Ferrous bisglycinate | Moderate | Gentlest — "gentle iron" | Chelated; well absorbed with fewer GI effects |
| Ferrous fumarate | High (~33%) | Middle ground | More iron per tablet, moderate tolerance |
| Ferrous gluconate | Low (~12%) | Milder than sulfate | Less iron per tablet; easier on the stomach |
| Heme iron (e.g., from beef liver) | Varies | Generally well tolerated | Absorbs via a different pathway; pricier |
| Iron + vitamin C combos | Varies | Depends on the iron form | Vitamin C boosts non-heme iron absorption |
02Why Bisglycinate Is Called "Gentle Iron"
Ferrous bisglycinate (iron chelated to the amino acid glycine) absorbs through a different pathway than iron salts, which means less free iron sitting in the gut causing irritation. Studies comparing it to ferrous sulfate generally find similar or better absorption with significantly fewer digestive complaints. If you've quit iron before because of nausea or constipation, bisglycinate is the form to try — it's the single most useful distinction on this page.
03Elemental Iron: The Number That Matters
Labels list the compound weight, but your body cares about elemental iron. A 325 mg ferrous sulfate tablet contains about 65 mg of elemental iron; a 300 mg ferrous fumarate tablet has about 100 mg. When comparing products — or following a provider's recommendation of a specific elemental dose — do the conversion. The NIH lists the RDA at 8 mg/day for adult men and 18 mg/day for premenopausal women (27 mg in pregnancy).
04Test Before You Supplement
Unlike most supplements on this site, iron deserves a blood test first (ferritin plus hemoglobin/hematocrit). Too little iron causes fatigue and anemia; too much accumulates — the body has no active way to excrete excess iron, and overload damages the liver, heart, and pancreas. Men and postmenopausal women rarely need iron unless a cause is identified. If you're tired and guessing, test first; don't supplement on a hunch.
05Tips for Absorption (and Tolerance)
- Take with vitamin C (or orange juice) — it meaningfully boosts non-heme iron absorption.
- Avoid taking with coffee, tea, or calcium — tannins and calcium inhibit absorption. Space them an hour or two apart.
- Take on an empty stomach if you can tolerate it — absorption is best, but if it causes nausea, taking it with a small meal is far better than quitting.
- Start low — you can split tablets or take every other day; alternate-day dosing may actually absorb better per dose.
Frequently Asked Questions
Which iron is easiest on the stomach?
Ferrous bisglycinate — widely sold as "gentle iron." It's chelated to glycine, absorbs well, and causes far fewer digestive complaints than ferrous sulfate in comparative studies. If iron has ever made you nauseous, start here.
How much elemental iron is in ferrous sulfate 325 mg?
About 65 mg. The 325 mg is the weight of the whole compound; only ~20% is elemental iron. Always convert when comparing products or following dosing advice.
Can I take iron every day?
Only if you have a reason to — confirmed low ferritin or a provider's recommendation. The body can't excrete excess iron, so indefinite daily use without monitoring isn't wise, especially for men and postmenopausal women.
Why does iron cause constipation?
Unabsorbed iron irritates the gut lining and alters gut motility — ferrous sulfate is the worst offender because a larger fraction goes unabsorbed. Bisglycinate, lower doses, and adequate hydration and fiber help.
Where can I buy gentle iron in Richmond, CA?
William's Natural Foods at 12249 San Pablo Ave, Richmond, CA 94805 carries iron in gentle forms including bisglycinate, plus vitamin C to pair with it. Open Monday–Friday 9 AM–7 PM, Saturday 9 AM–6 PM, Sunday 10 AM–5 PM. Call (510) 232-1911 to check what's on the shelf.
Still Have Questions? Come Talk to Us In Store
The fastest way to get answers is to talk it through in person. Here's how:
This article is for informational purposes only and is not medical advice. Get your iron levels tested (ferritin) before supplementing, and keep iron supplements away from children — overdose is dangerous. Talk to your healthcare provider first. These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease.