Running is one of the highest-demand sports for iron, vitamin D, and cardiac health. Yet most runners only get their bloods checked when something goes wrong. A proactive panel — run at least once a year — can be the difference between a personal best and a plateau.
Why Runners Are at Higher Risk of Deficiency
Running creates specific physiological demands that raise your risk of several deficiencies:
- Foot-strike haemolysis — each footstrike mechanically destroys red blood cells in the plantar capillaries, increasing iron turnover
- GI blood loss — endurance running causes low-level gut bleeding in around a third of marathon runners
- Sweat losses — zinc, magnesium, and sodium are all lost in significant quantities during long runs
- Cortisol elevation — high training loads chronically elevate cortisol, suppressing recovery and immune function
- Relative Energy Deficiency in Sport (RED-S) — underfuelling relative to training volume causes hormonal disruption in both men and women
The Recommended Runner's Blood Test Panel
| Test | Why It Matters for Runners | Target |
|---|---|---|
| Ferritin | Iron stores — depleted by haemolysis, sweat loss, and GI bleeding | >70 µg/L for athletes |
| Haemoglobin + MCV | Confirms anaemia and guides cause | Women ≥130, Men ≥140 g/L |
| Transferrin saturation | Confirms iron is being delivered to cells | >20% |
| Vitamin D | Critical for bone health, muscle function, and injury prevention | 75–150 nmol/L |
| B12 + Folate | Needed for red cell production — plant-based runners especially at risk | Normal range |
| CRP + ESR | Inflammation screen — elevated after overtraining or stress fractures | CRP <3 mg/L |
| Cortisol (morning) | High cortisol = overtraining; low cortisol = adrenal fatigue | 350–550 nmol/L (8–9am) |
| Testosterone (men) | Suppressed by high training volume — affects recovery, libido, motivation | 12–35 nmol/L |
| Oestradiol + LH/FSH (women) | RED-S and low bone density risk if oestrogen is suppressed | Normal for cycle phase |
| Thyroid (TSH + free T4) | Subclinical hypothyroidism impairs aerobic capacity and recovery | TSH 0.4–2.5 mIU/L |
| Troponin + BNP (marathon runners) | Cardiac strain markers — elevated acutely post-race but worth checking at rest | Undetectable at rest |
| Lipids + HbA1c | Cardiovascular baseline — running protects but doesn't guarantee | LDL <3.0 mmol/L |
When to Test
Timing matters. Test after a rest day — not within 48 hours of a hard session, as CRP, ferritin, and even haemoglobin can be artificially skewed. Ideal timing is mid-base phase, when training load is moderate and you haven't recently raced. Annual testing is a reasonable minimum; twice yearly for those training for marathons or ultras.
Signs You Should Test Sooner
- Unexplained performance drop — particularly aerobic capacity (high RPE at low pace)
- Fatigue that isn't resolving with rest
- Recurrent infections, particularly upper respiratory
- Muscle cramping or weakness beyond normal DOMS
- Mood changes, irritability, or loss of motivation to train
- Hair thinning, especially in female runners
Runner's Blood Test in Surbiton
Our sport-focused panel covers iron, hormones, inflammation, and cardiac markers — with same-week results and GP review.
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