Iron deficiency without anaemia affects 15 to 35% of female runners and 5 to 11% of males. Haemoglobin stays normal. Your GP says you're fine. But ferritin is depleted, performance declines 3 to 4%, and every run feels harder than it should. The only way to catch it is a blood test that actually checks ferritin. Most GP panels don't. A comprehensive panel like the TrueVitals Ultimate checks ferritin alongside 113 other markers that matter for endurance athletes.
Every stride you take destroys red blood cells. It's called foot-strike haemolysis: the mechanical impact of your foot hitting the ground ruptures erythrocytes in the capillaries of your feet. Research in the Journal of Applied Physiology confirmed that foot-strike is the primary cause of exercise-induced haemolysis in runners. A single run is not a problem. But across months of 40, 50, or 80-mile weeks, the cumulative damage drains your iron stores.
Foot-strike haemolysis is not the only mechanism. Runners lose iron through increased GI blood loss during long runs (blood diverts away from the gut, causing micro-bleeding), iron loss in sweat (significant in high volumes), menstrual losses in female runners, and increased red blood cell turnover from training stimulus. All of these compound.
Your reserves are draining but your body is still compensating. No obvious symptoms yet, but training adaptation may already be blunted. This is where most runners sit without knowing it. Your GP says everything is fine because haemoglobin is normal.
Reserves are critically low. Fatigue creeps in. Workouts feel harder than they should. Recovery takes longer. A 2025 systematic review (Pengelly et al., Journal of Sport and Health Science) found that IDNA reduces endurance performance by 3 to 4% and impairs VO2 max and mitochondrial function. In a half-marathon, that's 3 to 6 minutes. Your GP still says you're fine.
Only now does haemoglobin fall below range. Only now does your GP detect it. By this stage, performance has been declining for months or years, training has felt progressively harder, and the runner has likely blamed fitness, motivation, or overtraining. The problem was detectable at stage 1 with a ferritin test.
The target: Sports medicine practitioners recommend a minimum ferritin of 30 to 40 ng/mL for female runners and 40 to 50 ng/mL for males. Optimal endurance ranges are 50 to 70 ng/mL or higher. The NHS flags ferritin as low only below 15 ng/mL. That 15 to 50 gap is where most runner iron problems live: technically "normal," functionally depleted.
Iron is the most common deficiency. It's not the only one. Runners have specific physiological demands that affect multiple systems.
Vitamin D insufficiency increases stress fracture risk by up to 3.6 times in athletes. It affects approximately 57% of UK adults in winter. For runners putting repetitive impact through their bones, vitamin D status is directly relevant to injury risk. Aim for 75 to 125 nmol/L. The NHS flags deficiency only below 25 nmol/L.
Thyroid dysfunction mimics overtraining exactly: fatigue, weight gain, poor recovery, declining performance. Without testing, the two are indistinguishable. A runner who reduces training volume because they think they're overtrained when they actually have subclinical hypothyroidism will get worse, not better. Full thyroid (TSH, Free T3, Free T4, antibodies) separates them in a single test. Thyroid blood test guide.
Overtraining syndrome produces a characteristic blood pattern: suppressed testosterone, elevated or persistently high cortisol, rising cortisol-to-testosterone ratio, depressed Free T3, elevated hs-CRP that doesn't resolve between sessions, and suppressed white blood cell count. No single marker diagnoses it. The pattern across markers does. Serial testing (every 3 to 6 months during heavy training blocks) tracks whether you're adapting or accumulating fatigue.
hs-CRP rises acutely after hard training. That's normal and desirable — it's the inflammatory stimulus that drives adaptation. The problem is hs-CRP that fails to return below 1.0 mg/L between sessions. Persistently elevated CRP indicates insufficient recovery, chronic overload, or underlying illness. CK (creatine kinase) is also elevated after training but should return to baseline within 7 to 14 days. CK that doesn't resolve suggests ongoing muscle damage beyond normal training stress.
B12 and folate are essential for red blood cell production and oxygen transport. Deficiency impairs haemoglobin synthesis and reduces oxygen-carrying capacity — exactly what a runner cannot afford. Magnesium is depleted through sweat and is required for muscle contraction, nerve function, and energy metabolism. HbA1c and fasting insulin reveal metabolic efficiency, which directly affects fuel utilisation during long runs.
The TrueVitals Ultimate panel covers ferritin, full iron studies, vitamin D, full thyroid with antibodies, cortisol, testosterone, SHBG, hs-CRP, B12, folate, and 100+ additional markers. 114 biomarkers. Results in 48 hours. £349.
NHS lab reference ranges are derived from general population data. They define "normal" as the central 95% of the population — most of whom do not run 30+ miles per week. For athletes, "normal" is not optimal and "in range" can mask significant deficiency.
The TrueVitals report uses evidence-based optimal ranges alongside standard reference ranges. It flags markers that are technically "in range" but functionally suboptimal for an active person. Your ferritin at 22 ng/mL is not "normal." It's depleted for a runner, and the report will tell you that.
Pre-season baseline (October-November): test before UK vitamin D levels drop and before marathon training blocks intensify. This is your reference point for the training cycle ahead.
Mid-season check (March-April): for runners doing spring marathons, test midway through the training block. Iron, thyroid, and cortisol are the markers most likely to shift during heavy training.
Post-race recovery (2-3 weeks after a target race): CK, hs-CRP, and iron markers are elevated immediately after a marathon. Wait 2 to 3 weeks for acute inflammation to resolve, then test to see what the training block actually cost your body and where repletion is needed.
Minimum recommendation: annual testing for any runner doing 25+ miles per week. Twice-yearly for competitive runners, those with a history of iron issues, or anyone training for marathons or ultras.
Timing tip: avoid testing within 48 hours of a hard session or long run. CK, CRP, cortisol, and liver enzymes (AST, ALT) are all transiently elevated by intense exercise and will give misleadingly high readings. Test after a rest or easy day.
Most blood test reports are written for the general population. A CK of 300 U/L gets flagged as "high." For a runner 3 days after a long run, it's expected. The TrueVitals report applies athlete-aware context where relevant. It identifies the iron-thyroid-cortisol patterns that indicate overtraining, flags nutrient levels against optimal ranges for active people, and provides specific recommendations for supplementation doses, timing, and forms that address the unique demands of endurance training.
Serial testing builds the picture. Your first test is a snapshot. Your second, 6 to 12 months later, shows what the training block did to your body. Ferritin trending down? Iron supplementation or dietary changes before the next block. Cortisol trending up while testosterone trends down? Training load may be outpacing recovery. These trends are only visible with repeat testing.
114 biomarkers including ferritin, full iron studies, vitamin D, thyroid, cortisol, testosterone, and every marker that reveals whether your body is adapting or breaking down. Results in 48 hours.
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