The Athlete Paradox: Why Active Women Are Often the Most Iron-Deficient

You exercise regularly. You eat reasonably well. You prioritise recovery. So why does every session feel harder than it should? Why is your stamina not matching your effort?

Before you assume you've overtrained, there's a question worth asking first: when did you last check your ferritin?

For active women, iron deficiency is one of the most common and consistently under-diagnosed performance blockers, not because it's rare, but because its symptoms look exactly like what we expect training fatigue to feel like. And by the time standard blood tests catch it, you've often been running on empty for weeks.

Why Active Women Are Specifically at Risk

Women already have a higher baseline iron requirement than men, primarily because of monthly menstrual blood loss. Add regular training to that, and multiple mechanisms begin working against iron retention simultaneously.

A retrospective study of 336 female Division I collegiate athletes found that 57.7% had ferritin levels below 40 ng/mL at pre-participation screening — a level that many sports medicine practitioners consider sub-optimal for athletic function. A separate 2022 case study of highly trained non-professional female endurance athletes found that 46% had sub-optimal iron stores, despite training at volumes comparable to elite competitors and winning international age-group competitions.

Iron deficiency is estimated to affect 15–35% of female athletes compared to just 3–11% of male athletes. 

The pattern is consistent across sport types, age groups, and training levels. Being active and being iron-sufficient are not the same thing — and for women, the gap between them is particularly wide.

What Training Does to Your Iron Stores

Foot-Strike Hemolysis

Every ground contact during running creates mechanical force that ruptures red blood cells in the capillaries of your feet. A scoping review of marathon and ultramarathon runners found that iron levels dropped by 28% post-race — from 103 µg/dL to 73 µg/dL with foot-strike hemolysis identified as a key contributor. Minimally cushioned footwear and hard surfaces amplify this effect.

The Hepcidin Spike

This is the mechanism that catches most people off guard. After intense exercise, the liver releases a hormone called hepcidin, which actively suppresses iron absorption from the gut — precisely when the body is trying to recover.

A study published in The Journal of Nutrition measured this directly: a single prolonged run increased hepcidin by 51% and reduced fractional iron absorption by 36%. Hepcidin typically peaks 3–6 hours post-exercise and can remain elevated for up to 24 hours. This means the meal you eat after training delivers meaningfully less iron than the same meal eaten at rest.

Practically: taking iron supplements immediately post-workout may be the worst timing possible. First thing in the morning, before training, is when hepcidin tends to be lowest making it the most effective window for absorption.

Why Your Blood Test Might Miss It

This is where most people get tripped up. A standard blood panel checks haemoglobin which is the protein that carries oxygen in red blood cells. But haemoglobin can read as completely normal while iron stores are already depleted.

That's because the body prioritises red blood cell production for as long as possible, drawing down on stored iron first. Ferritin is the protein that stores iron and falls well before haemoglobin does. By the time haemoglobin drops, you've often been iron-depleted for weeks.

What to ask for specifically: serum ferritin.

In general medicine, the clinical threshold for deficiency is often set at 12–15 ng/mL. That's where symptoms of overt anemia appear. Sports medicine practitioners increasingly use a higher functional benchmark for active women like 35-40 ng/mL as a floor, with a range of 50–70 ng/mL considered optimal for training, recovery, and injury resilience. Below 30 ng/mL, even without anaemia, athletes commonly experience impaired oxygen delivery, elevated perceived effort, and reduced capacity to adapt to training.

What Low Iron Actually Feels Like

Iron deficiency without anaemia doesn't announce itself clearly. It creeps in gradually, and it looks like this:

• Effort that feels disproportionate to pace or output

• Heavy legs from the start of a session, before you've warmed up

• Fatigue that rest doesn't seem to resolve

• Slower recovery between training days

• A steady, unexplained decline in performance over weeks

• Elevated heart rate at moderate intensities

• Reduced motivation and flat mood

This overlaps almost completely with overtraining syndrome. The natural response is to back off, rest more, reduce load. But if the underlying cause is iron deficiency, rest doesn't restore it. The deficit remains, and performance continues to decline while you wait for a recovery that isn't coming from rest alone.

The Absorption Problem

Even when active women increase dietary iron, absorption is the limiting factor. Non-heme iron — from sources like lentils, spinach, and fortified foods  absorbs at just 2–5%. Heme iron from animal sources absorbs better, at 15–25%, but many women, particularly those eating plant-forward or vegetarian diets, rely heavily on non-heme sources.

Layer that with post-exercise hepcidin suppressing absorption, and it becomes clear why eating more iron-rich food doesn't always close the gap. How iron is absorbed matters as much as how much you consume.

For pairing: vitamin C consumed alongside iron meaningfully improves non-heme absorption. Calcium, tea, coffee, and most mineral supplements compete for the same absorption pathway and should be separated by at least an hour or two.

One Caveat: More Is Not Always Better

Iron is not a supplement you should increase without testing first. The body has a limited capacity to excrete excess iron, and elevated ferritin can reflect iron overload, chronic inflammation, or underlying conditions like haemochromatosis. Supplementing without knowing your baseline is guesswork and potentially harmful.

Get tested before supplementing. Then retest. The goal is a specific target range, not an indefinite increase.

The Takeaway

If you're a woman who trains regularly and is experiencing fatigue, stalled performance, or recovery that never quite completes — iron is worth investigating before you assume you've done too much.

The research is consistent: active women are at significantly elevated risk of iron deficiency; the symptoms are easy to misread as overtraining; standard haemoglobin tests miss it; and the performance cost is real and measurable.

Ask for ferritin. Know your number. Your training is doing the work — make sure your body has what it needs to actually recover from it.

References: 

• Prevalence of Iron Deficiency in Female Collegiate Athletes, Journal of Women's Sports Medicine (2022)

• Sims et al., Iron Deficiency in Highly Trained Non-Professional Female Endurance Athletes, IJERPH (2022)

• Iron Deficiency in Athletes: Prevalence and Impact on VO2 Peak, Nutrition / ScienceDirect (2024)

• A Prolonged Bout of Running Increases Hepcidin and Decreases Dietary Iron Absorption, The Journal of Nutrition (2022)

• Iron Deficiency, Supplementation, and Sports Performance in Female Athletes: A Systematic Review, ScienceDirect (2024)

• Foot-strike Hemolysis: A Scoping Review of Long-Distance Runners, Kansas Journal of Medicine (2025)