Endurance sport, iron and the transition: why the ferritin test matters more, not less

The HerStack editors. 2026-09-15.

There is a tidy story about iron and midlife that goes: periods stop, monthly iron loss stops, so iron stops being a question. For a woman who is still training hard, the research does not support the tidy story. A 2025 survey of 187 female runners, cyclists, swimmers and triathletes aged 40 to 60 found a population that keeps training and racing straight through the transition [7]. For those women, the sport itself moves iron around, and the one study that has looked at post-menopausal endurance runners suggests the effect lasts longer after menopause, not shorter.

What the female-athlete literature already knows

Iron is a working part of oxygen transport and energy metabolism, and it is the nutrient athletes most often come up short on. A 2019 narrative review put low iron status at roughly 15 to 35 per cent of female athlete cohorts, against 5 to 11 per cent of male cohorts, with endurance athletes over-represented [1]. A 2025 systematic review of 23 studies in 669 high-level female athletes, aged 13 to 47, opened with the figure that up to 60 per cent of female athletes experience iron deficiency, and found that deficiency was associated with endurance performance around 3 to 4 per cent lower [6]. The supplementation studies in that review were of athletes with a diagnosed deficiency, at daily doses of elemental iron far above what a shelf supplement provides, under supervision.

Why athletes, and why endurance in particular? Menstrual loss is one route, but it is not the only one [2]. Three mechanisms belong to the training itself.

Hepcidin. Exercise raises hepcidin, the hormone that governs iron absorption and recycling. An individual-participant meta-analysis pooling the available studies found exercise associated with a 1.5 to 2.5-fold rise, peaking three to six hours after a session, with the size of the rise driven mostly by how long the session lasted [3]. While hepcidin is up, iron from the meal you eat afterwards is absorbed less well. Long sessions, day after day, mean more of each day spent in that window.

Losses through the body. Foot-strike haemolysis (red cells damaged by impact), sweat, urine and the gut all cost iron. A study of 98 middle-aged men and women walking for nearly nine hours a day on four consecutive days watched plasma iron fall day on day: 8 per cent of participants were below the reference value at baseline and 43 per cent were by day four, with the authors attributing the change to haemolysis, sweat and urine losses and the body's immune response to prolonged exercise [4]. Those were walkers, not racers, aged 51 to 59 on average.

The immune signal. The rise in hepcidin follows a rise in interleukin-6, an immune messenger released by working muscle [3]. That is why the hepcidin response scales with duration, and why baseline ferritin, the body's stored iron, shapes how big the response is.

The one study in post-menopausal endurance runners

The 2020 study by Alfaro-Magallanes and colleagues is small, 13 endurance-trained post-menopausal women in their early fifties, and it is the only one of its kind we could find [5]. They ran eight three-minute efforts at 85 per cent of maximal aerobic speed and gave blood before, immediately after, and three and 24 hours later.

Hepcidin peaked at three hours, as it does in pre-menopausal women. The difference was at 24 hours: it had not returned to the pre-exercise level, where the literature in younger women would expect it to have done. The authors read this as a slower return of baseline hepcidin after menopause, and they raised the practical implication themselves: the timing of iron intake around training may need to be different for post-menopausal athletes than the standard advice assumes [5].

They also made the point that cuts the other way. Once menstrual losses stop, iron tends to accumulate in the body over the years, and the authors note that accumulation is not benign [5]. A post-menopausal athlete can be iron-low because training drains her, or iron-high because nothing is draining her any more. The two call for opposite responses, and neither can be told apart from the outside.

What a UK reader can take from this

Test before you supplement, and that applies more after menopause, not less. Our exercise guide already says ferritin first, dose second. This literature is the reason. The supplementation studies that show anything were in athletes with a measured deficiency, at medical doses [6], and the 2015 review of dietary approaches for female athletes notes that supplementation has been criticised for side effects and for the risk of iron toxicity [2]. A ferritin test through a GP or a reputable UK testing service settles which side of the line you are on.

Food first, and timing may matter. The same 2015 review found that dietary approaches, an iron-rich diet with haem sources and iron-rich products added to daily meals, can assist in maintaining iron status in female athletes during heavy training [2]. Haem iron comes from meat and fish; non-haem iron from pulses, dark green vegetables and fortified breakfast cereals, absorbed better alongside vitamin C and less well alongside tea or coffee. Given the hepcidin window, the iron-rich meal is better placed well away from the hard session than straight after it [3, 5].

What the register lets us say. Iron carries GB-authorised health claims, and we quote them as written: "Iron contributes to normal formation of red blood cells and haemoglobin", "Iron contributes to normal oxygen transport in the body" and "Iron contributes to the reduction of tiredness and fatigue". Each applies to a food or supplement that is at least a source of iron. We make no statement beyond that wording, and none of it is a reason to take iron without a test.

For the full picture on loading muscle and bone through the transition, including the iron form we card and why, see our exercise guide. For the testing options available in the UK, see our testing guide.