Supplements for Runners: What the Evidence Says
The Nutritional Demands of Running
Running β particularly high-mileage training β creates nutritional demands that differ from gym-based training:
- Iron loss: Foot-strike haemolysis (red blood cells are destroyed by the impact of each footstrike) increases iron losses. Sweating adds to this. - Bone stress: Repeated impact increases bone remodelling demands, requiring calcium and vitamin D. - Inflammatory load: Endurance running is an inflammatory stress β anti-inflammatory nutrients become more important. - Glycogen depletion: Long runs require carbohydrate replenishment strategies. - Electrolyte loss: Substantial sodium, magnesium, and potassium lost in sweat.
Priority 1: Iron
Iron deficiency anaemia is one of the most common performance-limiting conditions in female runners. A 2019 review found that 17β35% of female distance runners have iron deficiency (measured by ferritin < 20 ΞΌg/L), compared to 3β7% of the general female population.
Symptoms of deficiency: Unexplained fatigue, reduced VO2 max, impaired recovery, increased perceived exertion at usual paces.
Testing: Ask your GP for a ferritin test alongside a full blood count. A ferritin of < 20 ΞΌg/L in an athlete warrants treatment; many sports medicine practitioners target > 50 ΞΌg/L for optimal athletic performance.
Supplementation: Iron bisglycinate is best tolerated. 14β25mg elemental iron for maintenance; higher doses under GP supervision for repletion.
Priority 2: Vitamin D3
Stress fractures are a significant injury risk for runners. Vitamin D is essential for bone mineralisation and calcium absorption.
A 2012 study of military recruits found that stress fracture incidence was inversely correlated with baseline vitamin D levels. Studies in athletes show vitamin D supplementation may also support muscle recovery and reduce inflammation.
Dose: 2,000 IU D3 daily through autumn and winter. Test at start of season.
Priority 3: Omega-3
Endurance running creates significant inflammatory load. EPA and DHA act as precursors to anti-inflammatory prostaglandins and reduce exercise-induced inflammation.
A 2015 study found omega-3 supplementation reduced soreness and improved neuromuscular function after eccentric exercise. For runners: potential reduction in DOMS, improved recovery between sessions.
Dose: 2β4g EPA+DHA daily.
Priority 4: Magnesium
Magnesium losses in sweat during long runs are significant. Deficiency impairs muscle function, increases cramping risk, and disrupts sleep (which is when recovery occurs).
Dose: 300β400mg magnesium glycinate or malate daily. Malate may be particularly appropriate (malic acid is involved in energy production).
Priority 5: Caffeine
The most evidence-based acute performance-enhancing substance in endurance sport. Meta-analyses consistently show 2β3% improvement in endurance performance at doses of 3β6mg/kg.
Protocol: 3β5mg caffeine per kg bodyweight, 45β60 minutes before a race or quality session. Most useful for races and hard efforts β not every run.
For Marathon Training Specifically
Beetroot / Dietary Nitrate: Dietary nitrates (from beetroot juice or concentrate) reduce the oxygen cost of submaximal exercise by improving mitochondrial efficiency. A 2011 meta-analysis showed improvements in time trial performance. Most effective in trained athletes at higher intensities.
Protocol used in research: 500ml beetroot juice daily for 6 days before an event, or 70β140ml concentrated shot 2β3 hours before.
Carbohydrate + Electrolytes: Not a supplement per se, but for runs over 90 minutes, consuming 30β60g carbohydrate per hour with electrolytes (particularly sodium) is evidence-based. Practice this in training before racing.
Supplements with Little Evidence for Runners
| Supplement | Reality | |-----------|---------| | BCAAs | If you're eating adequate protein (1.4β1.7g/kg for endurance), redundant | | Glutamine | No benefit for immune function or recovery in healthy athletes with adequate nutrition | | HMB | Modest evidence in strength sports; weaker for endurance | | Adaptogen stacks | May reduce training adaptation signal if cortisol is suppressed too aggressively |
Recovery-First Principle
For runners, sleep and adequate calorie intake are the highest-leverage recovery factors. No supplement stack overcomes a chronic calorie deficit (a significant issue in female runners, contributing to Relative Energy Deficiency in Sport β RED-S).
If you're tired all the time and not recovering between sessions, address your total energy intake before adding supplements.
Get a blood test (ferritin, vitamin D, full blood count) before your training season starts. Identify deficiencies, then correct them.
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