I will give you the short answer first, because most pages on this question bury it.
Everything below is why that gap exists, what it costs, and where the ceiling is. This last part matters, because the honest answer includes a limit that most content on this topic leaves out.
Why nobody can give you one number
A laboratory reference range is a statistical description of a sampled population. It is not a definition of health, and it was not built with trained female athletes in mind.
An athlete's iron demand is different in ways that compound. Higher red cell turnover, losses through sweat and gut, foot-strike haemolysis in running sports, and for many, menstrual blood loss on top of all of it. The same ferritin value does not carry the same meaning in a sedentary population and in someone training fifteen hours a week.
So rather than looking for an authoritative number that does not exist, the more useful question is what threshold the research on athletes actually uses when it decides who counts as deficient.
What the athlete research uses
The most relevant piece of work here is a 2024 systematic review in the Journal of Sport and Health Science, covering 23 studies and 669 female athletes aged 13 to 47 across 16 sports.
Its inclusion criteria are the interesting part. It defined its population as high-level female athletes with serum ferritin below 40 micrograms per litre, where high-level meant a maximal oxygen uptake above 45 mL/kg/min or more than five hours of training a week.
It also reports that up to 60 per cent of female athletes experience iron deficiency. That is not a fringe problem in this population. It is closer to a default.
The mismatch with your lab slip
Most laboratory lower limits for ferritin sit somewhere between about 10 and 30 micrograms per litre depending on the lab. A threshold of 40 sits above all of them.
That mismatch is the whole reason this question keeps getting asked. An athlete gets a result of 25, is told it is within range, and is left with no explanation for why her sessions feel harder than they should.
What the deficiency actually costs
The same review puts numbers on it, and they are worth knowing because they are smaller than the internet suggests and larger than a dismissive GP suggests.
| Measure | What the review found |
|---|---|
| Endurance performance, when deficient | reduced by 3 to 4 per cent |
| Endurance performance, after treatment | improved by 2 to 20 per cent |
| Maximal aerobic capacity, after treatment | improved by 6 to 15 per cent |
| Isokinetic strength and anaerobic power | may be impeded, but the range spans -23 to +4 per cent |
Three to four per cent does not sound like much until you convert it. In a three-hour event that is five to seven minutes. In a field of closely matched athletes it is the difference between selection and not.
The treatment figures came from about 100 mg of elemental iron per day for up to 56 days in the oral studies, and aerobic capacity gains came from 16 to 100 mg a day across 36 to 126 days. These are not overnight interventions.
The strength and power picture is genuinely unclear
Notice the width of that last row. The review found effects on isokinetic strength and anaerobic power ranging from a 23 per cent decrement to a 4 per cent improvement, and the effect of supplementation on anaerobic power varied from -5 to +9 per cent.
A range that crosses zero in both directions means the honest answer is that we do not know yet. Anyone quoting you a confident strength benefit from iron is reading a range as a result.
My own work on this, including what is wrong with it
I led a systematic review and meta-analysis on intravenous iron in adults with iron deficiency without anaemia, published in the Journal of Cachexia, Sarcopenia and Muscle. It pooled 21 randomised controlled trials and 3,514 participants.
What we found: intravenous iron significantly improved physical function, measured as peak oxygen consumption, by a mean difference of 1.77 mL/kg/min, with a 95 per cent confidence interval of 0.57 to 2.97. Fatigue improved. Quality of life did not shift overall.
What I want to be straight about, because it is in our own abstract: we rated the quality of the evidence low or very low for every outcome except fatigue, mostly because most included studies carried a high risk of bias. That is our conclusion about our own paper, and it should temper how hard anyone leans on the number.
A second meta-analysis, in women of reproductive age specifically, found daily oral iron improved relative maximal oxygen uptake by 2.35 mL/kg/min, 95 per cent confidence interval 0.82 to 3.88, across 18 studies. It also found submaximal benefits, a lower heart rate and a lower percentage of maximum required to hold a given workload. Only three of its studies were at overall low risk of bias.
So the direction of effect is consistent across three independent bodies of work. The precision is not what anyone would like it to be.
The ceiling, which is the part usually left out
Everything above is about correcting a deficiency. It is not an argument for pushing iron as high as possible, and the distinction is the one that matters most for an athlete who already tests fine.
Raising iron status in someone who is not deficient has not been shown to consistently improve performance. Iron is also not a free intervention. The body has no mechanism for actively excreting it, oral supplements carry a real side-effect burden, and iron overload is a genuine clinical problem rather than a theoretical one.
The benefit lives in avoiding deficiency, not in accumulating iron. Treating ferritin as a score to maximise is a misreading of the whole literature.
What to do with this
- Get the number, and get it with company. Ferritin alone is the weakest version of the test. Transferrin saturation tells you about iron in circulation, and CRP tells you whether inflammation is inflating the ferritin reading.
- Time the test sensibly. Ferritin rises with inflammation, and hard training is inflammatory. A sample taken the morning after a brutal session can read higher than your real status.
- Do not accept "normal" as the end of the conversation if you are training seriously and your result is in the twenties or thirties. Ask specifically how your number sits against the thresholds used in athlete research rather than against the general population range.
- Budget months, not weeks. The trials that showed benefit ran 36 to 126 days.
- Find the cause. If you are losing iron faster than you can absorb it, supplementation is holding a line rather than fixing anything.
The bottom line
There is no single ferritin number every female athlete should hit, and the pages that give you one are inventing certainty.
What is defensible: the athlete literature works below 40 micrograms per litre, that threshold sits above most lab lower limits, up to 60 per cent of female athletes are deficient, deficiency costs roughly 3 to 4 per cent of endurance performance, and correcting it reliably helps while over-correcting it does not.
If you are training hard, feeling flat, and have been told your bloods are fine, the number is worth looking at again rather than accepting.
Work out your iron risk, and what to ask for
The individuals page has the free iron risk questionnaire, and plain-language guides.
See the individuals pageSources
Every figure above was read from one of these three papers directly.
- Pengelly M, Pumpa K, Pyne DB, Etxebarria N. Iron deficiency, supplementation, and sports performance in female athletes: a systematic review. Journal of Sport and Health Science 2025;14:101009. doi:10.1016/j.jshs.2024.101009
- Dugan C, Cabolis K, Miles LF, Richards T. Systematic review and meta-analysis of intravenous iron therapy for adults with non-anaemic iron deficiency: an abridged Cochrane review. Journal of Cachexia, Sarcopenia and Muscle 2022;13(6):2637-2649. doi:10.1002/jcsm.13114
- Pasricha SR, Low M, Thompson J, Farrell A, De-Regil LM. Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis. The Journal of Nutrition 2014;144(6):906-14. doi:10.3945/jn.113.189589
This article is educational and not medical advice. Never begin iron supplementation without testing, and always discuss changes to supplementation or testing with a qualified clinician who knows your full history.