- Ferritin is your iron storage protein; low levels are associated with reduced VO₂ max, slower recovery, and persistent fatigue
- Research consistently finds that a significant proportion of female endurance athletes, in some studies approaching half of those tested, have ferritin below thresholds associated with optimal performance[1]
- Standard blood panels often omit ferritin entirely; a full blood count (FBC) does not include it
- Addressing low ferritin is a gradual process that typically unfolds over months, under the guidance of a healthcare professional
- A blood test is the only way to know your level; always consult a healthcare professional before supplementing iron
What is ferritin and why does it matter for athletes?
Ferritin is the protein your body uses to store iron in your cells. When blood iron runs low, ferritin reserves are broken down to release iron for use. For endurance athletes, this chain matters enormously: iron is the backbone of haemoglobin, which carries oxygen from your lungs to your working muscles.
The pathway is direct:
Low ferritin → less available iron → lower haemoglobin → reduced oxygen delivery → lower VO₂ max
Because the depletion is gradual, most athletes with suboptimal ferritin have no idea. The decline feels like general fatigue, slower recovery, or a training plateau, easy to attribute to overtraining, poor sleep, or life stress.
What's the optimal ferritin level for an endurance athlete?
This is where standard medical advice and performance medicine diverge.
Laboratory "normal range" for ferritin is typically 12–300 µg/L for women and 30–400 µg/L for men. By these standards, a female athlete with ferritin at 14 µg/L is "normal."
Sports medicine research has proposed higher thresholds for endurance performance, with some studies suggesting that athletes may notice performance differences at levels well above the clinical lower limit. Commonly cited research thresholds are:
- Women: ≥60–80 µg/L
- Men: ≥80–100 µg/L
These are not clinical diagnostic thresholds; they are reference points from sports medicine literature. Your individual target should be determined in consultation with a healthcare professional based on your symptoms, training history, and full blood picture.
Athletes in that suboptimal zone, technically "normal" but below the performance threshold, frequently experience:
- Unexplained fatigue during training
- Slower recovery between sessions
- Declining performance despite consistent training
- Breathlessness at intensities that previously felt manageable
- Persistent low-grade illness
Why do endurance athletes deplete ferritin faster?
Several mechanisms drive iron depletion in endurance sport:
1. Foot-strike haemolysis. Repeated impact (running, Hyrox, triathlon) physically destroys red blood cells, releasing iron that's then excreted in urine. This is unique to impact sports.
2. Sweat losses. Iron is lost in sweat. Higher training volumes mean higher cumulative losses.
3. Hepcidin elevation. Intense exercise triggers a post-training rise in hepcidin, a hormone that blocks iron absorption from the gut for 3–6 hours. Athletes who train twice daily or eat immediately after sessions absorb less dietary iron than they expect.
4. Inadequate dietary intake. Plant-based athletes are particularly vulnerable; non-haem iron (from plants) is absorbed at roughly 5–10% efficiency, versus 15–35% for haem iron from meat.
Worth knowing: Low ferritin without anaemia is called "iron deficiency without anaemia." It's the earliest and most common stage, and the stage at which research suggests athletic performance may already be affected, even before haemoglobin falls outside the reference range.
How is ferritin measured?
Ferritin is measured via a standard venous blood draw. It's a single marker in a blood panel: simple, accurate, and available within 72 hours.
The key is that ferritin must be specifically requested. A standard full blood count (FBC) does not include ferritin. Many athletes have had "normal blood tests" that simply never tested it.
At Honed Health, ferritin is included in the Performance Panel alongside:
- Serum iron and transferrin saturation: to assess how well iron is being transported
- Haemoglobin and haematocrit: to detect functional anaemia
- Full blood count: for a complete picture of red blood cell health
What happens if you find low ferritin?
Restoring ferritin stores takes time. This is the most important thing to understand. If a blood test shows low ferritin, your healthcare professional may explore:
- The underlying cause: dietary insufficiency, absorption issues, blood loss, or haemolysis each have different management approaches
- Supplementation: oral iron is a common approach; intravenous iron may be used in more significant depletion under medical supervision
- Absorption factors: the timing and co-administration of iron supplements can affect how well they are absorbed
- Monitoring progress: ferritin levels respond gradually; retesting is typically recommended after an appropriate period, as guided by your healthcare professional
Important: Iron supplementation in people with normal or high ferritin can cause oxidative stress and harm. Always test before supplementing. Never supplement iron based on symptoms alone.
How long does recovery take?
Research suggests that changes in ferritin levels occur gradually, typically over several months rather than weeks. Subjective improvements in energy are often reported before measurable changes in laboratory markers, though individual responses vary significantly based on the degree of depletion, the underlying cause, and whether management is appropriately tailored.
Periodic retesting, as advised by a healthcare professional, is the most reliable way to track whether ferritin levels are trending in the right direction over time.
FAQ
Can I just take iron supplements without testing first?
No. Iron overload (haemochromatosis) is a real risk, and it's more damaging than deficiency. Iron supplementation should only be used when a blood test confirms deficiency, and should be supervised by a GP.
Is ferritin included in a standard blood test?
Not automatically. Ferritin is not part of a standard full blood count (FBC) and must be specifically requested as part of a blood panel. At Honed Health, ferritin is included in every Performance Panel as standard.
What foods are highest in iron?
Red meat, liver, oysters, and sardines are the richest sources of haem iron (highest absorption). Lentils, tofu, spinach, and fortified cereals provide non-haem iron (lower absorption; enhance with vitamin C).
How often should I test ferritin?
If you're actively correcting deficiency, retest every 12 weeks. Once in the optimal range, testing every 6–12 months is sufficient to catch seasonal depletion before it impacts performance.
Does running specifically cause more iron depletion than cycling?
Yes. Foot-strike haemolysis makes impact sports (running, Hyrox, triathlon) significantly more depleting than cycling or swimming. Runners need to monitor ferritin more frequently.
