Iron
Best-in-class: Iron Bisglycinate
Essential for hemoglobin, oxygen transport and energy. Thorne's bisglycinate is gentle on the gut versus ferrous sulfate, which commonly causes constipation and nausea.
Iron quick facts
| Suggested dose | 25 mg every other day is often as effective as daily and improves absorption (per recent hepcidin research). Take away from calcium/coffee. |
| How often | every other day |
| Who it's for | Menstruating women, endurance athletes, plant-based eaters, and anyone with confirmed low ferritin. |
The single most important test-first supplement there is. Ferritin under 30 causes fatigue, hair shedding, restless legs and flat mood well before hemoglobin drops — so the full blood count reads normal and the person feels terrible. Equally, iron is a pro-oxidant you cannot excrete: men and post-menopausal women rarely need it, and anyone with undiagnosed hemochromatosis is harmed by it. Never take it on a guess. Take away from calcium, coffee and tea, which all block absorption; vitamin C alongside improves it.
How Iron actually works
Iron sits at the center of the heme ring in hemoglobin and myoglobin, where it reversibly binds oxygen — that is the job everyone knows. The less discussed roles matter as much: it is the catalytic metal in the cytochromes of the electron transport chain, and a required cofactor for tyrosine hydroxylase and tryptophan hydroxylase, the rate-limiting enzymes making dopamine and serotonin. Bisglycinate is chelated to two glycine molecules, which lets it use amino-acid transport rather than competing at the DMT1 iron transporter, so absorption is better and the gut irritation that makes people abandon iron is much reduced.
Where to get Iron
Buy Iron Bisglycinate at Thorne →The evidence for Iron
Graded by what exists behind each claim.
✅ Clinically validated
- Corrects iron-deficiency anemia and reliably raises ferritin, hemoglobin and energy in deficient individuals (well-established in RCTs).
- Improves fatigue and exercise capacity in iron-deficient (even non-anemic) menstruating women.
📊 Correlative data
- Low ferritin is associated with fatigue, hair shedding, restless legs and reduced endurance performance.
🧪 Theoretical / extrapolated benefits
- Bisglycinate's chelated absorption pathway is proposed to reduce the pro-oxidant gut exposure of free iron — plausible but not a proven clinical outcome.
How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →
What Iron actually does
Iron is the supplement on this estate where a schedule beats a dose, and the reason is a 25-amino-acid peptide called hepcidin. Hepcidin is made by the liver, binds ferroportin -- the only known cellular iron exporter -- and causes it to be internalized and degraded. With ferroportin gone from the basolateral surface of the enterocyte, absorbed iron is trapped in a cell that will be shed in a few days.
Hepcidin responds to an oral iron dose, and it stays up for about a day. A study in iron-depleted women showed that oral iron supplements increase hepcidin and decrease iron absorption from doses given later Moretti 2015. That single observation is what makes daily dosing self-defeating: the second dose arrives while the first is still suppressing the door.
Absorption itself is a two-step process with a redox requirement. Ferric iron is reduced to ferrous by duodenal cytochrome b at the brush border, taken up by divalent metal transporter 1, and exported by ferroportin after re-oxidation by hephaestin. Ascorbate helps the first step, which is why vitamin C is co-administered; polyphenols in coffee and tea and divalent cations such as calcium compete at the second.
Exercise adds a third clock that athletes rarely account for. Iron status and the acute post-exercise hepcidin response have been characterized in athletes Peeling 2014: a hard session raises interleukin-6 and hepcidin with it, so a dose taken in the hours after training lands in the worst absorption window of the day. That is a timing fact with a practical consequence and it is on no label.
Cell, rodent, human — and where it stops
The schedule question has been tested directly, twice, and the answer is unusually clean for a supplement.
What has been measured in people. Two open-label randomized controlled trials in iron-depleted women compared iron absorption from supplements given on consecutive versus alternate days, and single morning doses versus twice-daily split dosing, using isotopic labels to measure fractional and total absorbed iron rather than inferring it Stoffel 2017. A subsequent randomized double-blind placebo-controlled study compared alternate-day against consecutive-day supplementation in iron-depleted women von Siebenthal 2023. A randomized trial had already shown that iron supplementation reduces fatigue in non-anemic menstruating women with low ferritin Vaucher 2012.
The first obstacle is that absorption efficiency and total absorbed iron are not the same endpoint. Alternate-day dosing raises fractional absorption; whether it raises total absorbed iron over a week depends on the comparison being made, which is exactly why both trials measured both Stoffel 2017 von Siebenthal 2023.
The second obstacle is that the trials were in iron-depleted women. Hepcidin is suppressed by iron deficiency, so the dynamics in a depleted person are not the dynamics in a replete one. The reviews of iron in human nutrition treat status as the governing variable rather than dose Brittenham 2023.
What would close the gap. Report hemoglobin and ferritin recovery over 12 weeks rather than absorption over one day, and include tolerability, because the reason alternate-day dosing may win in practice is that people keep taking it von Siebenthal 2023.
Iron — which form, and does it matter
Bisglycinate, sulfate, fumarate and gluconate differ in elemental percentage and in gut irritation, and the elemental number is the one to compare. Ferrous sulfate is roughly 20 percent elemental iron; fumarate about 33 percent; a glycine chelate delivers its elemental content with less local irritation. Whichever form, the hepcidin response is to absorbed iron, so a gentler salt does not escape the interval problem Moretti 2015.
Gentle describes the stomach and not the overload risk. That sentence is worth stating twice on any iron page, because the marketing for chelated forms implies a safety property they do not have Brittenham 2023.
Liquid and low-dose formulations exist for the same reason alternate-day dosing does. Lower single doses raise hepcidin less, which is the mechanistic argument for splitting the difference between dose and interval Stoffel 2017.
No filed panel for the vendor iron product on this site has been read. supplements_data.BLENDS holds no record for the Thorne iron bisglycinate product, so this page states no per-capsule elemental amount for it. The number to find on any iron label is elemental iron in milligrams.
What would have to be true, and how you would know it was not
1. The schedule prediction, which is the reason this page exists. Same weekly elemental iron, daily for 6 weeks against alternate-day for 6 weeks, with ferritin and hemoglobin at each end. Predict alternate-day dosing achieves at least as much repletion with better tolerance, because hepcidin stays elevated for roughly a day after a dose Stoffel 2017 von Siebenthal 2023 Moretti 2015.
2. The training-timing prediction, for athletes. Take the dose on a rest day morning rather than after a hard session. Predict better absorption, because post-exercise hepcidin rises Peeling 2014. Nobody has trialed this schedule directly and the mechanism is explicit.
3. The symptom prediction, in non-anemic deficiency. A fatigue scale plus ferritin at baseline and 12 weeks in a menstruating person with a low ferritin and a normal hemoglobin. Predict fatigue improves, which is the specific randomized finding Vaucher 2012.
4. The co-ingestion prediction. Two weeks with coffee or tea at the same time, two weeks separated by two hours. Predict a measurable difference in the ferritin trajectory, because polyphenols and calcium compete at the absorption step.
5. The stopping prediction, which cuts against habit. Predict that continuing past repletion raises ferritin without benefit, and that iron has no regulated excretion route to correct it Brittenham 2023. Iron supplementation is a course with an endpoint, not a daily habit.
What nobody has tested yet
Nobody has run the alternate-day schedule to a clinical endpoint over months. The absorption result is established Stoffel 2017 von Siebenthal 2023; hemoglobin recovery curves over a full repletion course have not been compared head to head at scale.
Nobody has tested the post-exercise timing rule. The hepcidin response to exercise is characterized Peeling 2014 and no trial has randomized dose timing around training.
Nobody has established the schedule in men or in post-menopausal women. The trials are in iron-depleted premenopausal women Stoffel 2017 Vaucher 2012, and hepcidin dynamics differ with baseline status Brittenham 2023.
And nobody has defined the ferritin at which to stop. Starting thresholds are debated and stopping thresholds are convention Brittenham 2023.
Iron — its own safety story, not its category's
The rule that belongs to iron above every other supplement is that nobody should take it without a measured reason. There is no regulated excretion route; absorbed iron leaves only through bleeding and cell loss, and overload damages liver, heart and pancreas silently before it declares itself Brittenham 2023. A ferritin, ideally with a transferrin saturation and an inflammatory marker, is what turns this from a guess into a decision.
Iron is the leading cause of fatal poisoning in young children. Child-resistant closure, high shelf, no exceptions. This is the one place where a supplement's packaging is a genuine safety control.
Gastrointestinal effects are the ordinary problem and they have a schedule solution. Constipation, nausea, dark stools and cramping are dose-related and are the usual reason people stop; alternate-day dosing improves both absorption and tolerability at once Stoffel 2017 von Siebenthal 2023, which is a rare case of the two pulling the same way.
The interactions are all absorption interactions. Iron binds levothyroxine, tetracyclines, quinolones and levodopa in the gut, so separate by four hours for thyroid hormone and two for the rest; coffee, tea and calcium reduce the iron. Anyone with hemochromatosis genes, and roughly one in two hundred people of Northern European descent carries them, reaches overload far more easily Brittenham 2023. Nothing here is medical advice or a diagnosis, and none of these statements has been evaluated by the Food and Drug Administration.
Sources read for this page
- Stoffel NU. 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
- von Siebenthal HK. Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study. EClinicalMedicine 2023 · PMID 38021373
- Moretti D. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood 2015 · PMID 26289639
- Peeling P. Iron status and the acute post-exercise hepcidin response in athletes. PLoS One 2014 · PMID 24667393
- Vaucher P. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ 2012 · PMID 22777991
- Brittenham GM. Iron. Adv Nutr 2023 · PMID 37422198
How you would know if it worked
These are the markers that recommend this product on their own pages, so they are the ones that should move if it is doing what it is sold for.
- Iron Panel (Iron, TIBC, Transferrin Saturation) — Iron bisglycinate, alternate-day dosing (better absorption than daily — daily dosing raises hepcidin and blocks uptake) Retest: With ferritin, every 3–6 months if supplementing or donating.
- Complete Blood Count (CBC) with Differential — Iron only if ferritin confirms deficiency (iron supplementation without deficiency is harmful) Retest: 3 and 6 months after starting TRT, then every 6–12 months.
- Ferritin — Iron bisglycinate 25–50 mg every other day — alternate-day dosing produces better absorption than daily, because daily dosing raises hepcidin and blocks uptake Retest: 8–12 weeks after starting iron; every 6 months if donating blood.
- TSH (Thyroid-Stimulating Hormone) — Zinc and iron support T4→T3 conversion Retest: 6–8 weeks after any dose change; annually if stable.
- Free T3 (Triiodothyronine) — Selenium 200 mcg (required cofactor for deiodinase enzymes), zinc 15–30 mg, iron if ferritin is low Retest: 6–8 weeks after intervention.
The cheapest panel carrying Complete Blood Count (CBC) with Differential and at least one other of these is Am I Iron Deficient?, at $18 — the panel is named for a different question, and the marker is the same marker. That is the whole cost of finding out.
Draw before you start, not after. A result with nothing to compare it to answers nothing.
Iron — safety & side effects
- Constipation, nausea, dark stools and stomach pain — extremely common, dose-related, and the main reason people stop. Taking it every other day rather than daily improves absorption *and* tolerability.
- Do not supplement iron without knowing your ferritin. Iron overload damages the liver, heart and pancreas, it is silent until it is not, and roughly 1 in 200 people of Northern European descent carry hemochromatosis genes that make it far easier to reach.
- Iron is the leading cause of fatal poisoning in children under six. Child-resistant cap, high shelf, no exceptions.
- Separate from thyroid medication by four hours. Minerals bind levothyroxine in the gut and reduce absorption enough to shift a stable TSH. It also binds tetracycline and quinolone antibiotics, and levodopa.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this against it with a pharmacist or doctor — pharmacists are underused and free.
- When to take it, and what to take it with
- Which form actually absorbs
- Who it's worth it for
- Best-in-class brand pick
- Coach Cam's stacks and notes
- Fasted or with food, and when in the day
- Morning or night, and why that window
- Around training, or deliberately away from it
- What it must not share a window with
Everything above is free and stays free. Skool is where it becomes a plan — Iron in an order, with the rest of what you're running.
Unlock in Skool — $10/mo →Bloodwork to run alongside Iron
Baseline first, then again at 8–12 weeks.
| Marker | What it’s watching for |
|---|---|
| Ferritin | Never supplement iron without this. Overload is harder to fix than deficiency |
| Iron Panel (Iron, TIBC, Transferrin Saturation) | Transferrin saturation catches overload that ferritin alone can miss |
| Hereditary Hemochromatosis, DNA | 1 in 200 carry it. Iron supplements are actively dangerous if you do |
| Complete Blood Count (CBC) with Differential | Confirms whether the deficiency has reached anemia yet |
The “Am I Iron Deficient?” panel covers these in one order — 2 markers, $16.20 with the discount applied.
Check results you already have → · All 103 markers A–Z
Iron — frequently asked questions
What is Iron?
Essential for hemoglobin, oxygen transport and energy. Thorne's bisglycinate is gentle on the gut versus ferrous sulfate, which commonly causes constipation and nausea.
What is the suggested dose of Iron?
25 mg every other day is often as effective as daily and improves absorption (per recent hepcidin research). Take away from calcium/coffee. This is a general reference for education only — statements have not been evaluated by the FDA and this is not medical advice.
Where can I find Iron dosing and the full breakdown?
The suggested dose and the full evidence — clinical, correlative and theoretical — are on this page. What's inside Skool is when to take it, which form actually absorbs, the brand worth buying and Coach Cam's stacks.
Where can I buy Iron?
Coach Cam sources Iron from Thorne, with 10% off auto-applied at checkout — use the buy link on this page.
Iron inside a finished plan
One arm of 4 Protocol Blueprints, free to read in full.
What Iron is used for
Iron appears under 6 goals in the goal router.
Related Minerals supplements
Where this goes next
Iron is the upstream-cause arm of this plan. The page above is the free breakdown of one compound; the plan it belongs to — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.