REF-776 · Hew-Butler et al., 2015 · Clinical Journal of Sport Medicine, Vol. · Paper · PubMed

Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

A-fairly strong evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

The third international consensus defines exercise-associated hyponatraemia (EAH) as a blood sodium concentration below the laboratory's normal range — for most laboratories below 135 mmol/L (full text, checked 2026-09-29: Definition).

Its central conclusion is that EAH, and every known death from it, is caused by drinking hypotonic fluid (water or sports drinks) beyond what is lost in sweat and urine, usually together with non-osmotic secretion of the antidiuretic hormone (full text, checked 2026-09-29: Summary of recommendations, Etiology 1, Grade 1A).

Prevention therefore targets drinking behaviour: drinking to thirst is the recommended strategy, sodium in drinks cannot prevent EAH in someone who overdrinks, and education plus fewer aid stations have lowered incidence in events.

Symptoms range from mild non-specific complaints to severe encephalopathy, and severity — not the sodium number — guides treatment, which for severe cases is intravenous hypertonic saline without waiting for a lab value.

Participants

Not applicable (consensus statement). Panel of 17 clinicians and scientists in sports medicine, nephrology, endocrinology, emergency medicine, exercise physiology and nutrition (full text, checked 2026-09-29: author list). Epidemiology cited in the statement: pooled from 27 studies, only 0.8% (19 of 2262) of recreational athletes started a race already hyponatraemic (full text, checked 2026-09-29: Epidemiology).

Protocol

Third international consensus development conference (Carlsbad, California, 2015), building on the 2005 and 2007 statements; recommendations graded with the American College of Chest Physicians scheme (full text, checked 2026-09-29: Table 1).

Key Results

Cause: over-consumption of hypotonic fluid relative to exchangeable sodium, likely with non-osmotic antidiuretic hormone secretion — the mechanism behind EAH and all known fatalities (Grade 1A). Under-replaced sodium losses lower sodium at any distance (Grade 1A), but there is little evidence that sodium loss is the primary mechanism of symptomatic EAH even in long, hot events (Grade 2C) (full text, checked 2026-09-29: Summary of recommendations).
Main risk factor: sustained fluid intake greater than sweat, respiratory and urine losses, so that a positive water balance builds; almost all symptomatic cases occurred in people who gained or held body weight during activity where some weight loss would be expected. Body-weight loss under 0.75 kg after a standard marathon has been associated with asymptomatic EAH (full text, checked 2026-09-29: Risk factors).
Prevention — thirst: using thirst to guide drinking should limit overdrinking while still preventing excessive dehydration (Grade 1C); the cues to drink persist in hot and cold conditions (full text, checked 2026-09-29: Prevention).
Prevention — sodium: sodium-containing sports drinks can slow the fall of blood sodium when intake roughly matches losses, but cannot prevent EAH when fluid intake stays excessive, because all sports drinks (about 10-38 mmol/L sodium) are far below blood (about 140 mmol/L) (Grade 1C) (full text, checked 2026-09-29: Sodium supplementation).
Prevention — events: athlete education and limiting fluid availability lowered EAH incidence in an Ironman; aid stations about 20 km apart on the Ironman bike and 5 km apart in a marathon have been associated with less EAH, though the optimal spacing needs study (Grade 1C) (full text, checked 2026-09-29: Education and event management).
Recognition and treatment: symptoms range from mild non-specific complaints to severe encephalopathy, and symptom severity, not the absolute sodium value, guides therapy (Grade 1A). In a hyponatraemic athlete, hypotonic or isotonic fluids are withheld until urination (Grade 1C).Suspected severe EAH is treated immediately with intravenous hypertonic saline (for example a 100 mL bolus of 3% NaCl, repeatable) without waiting for a lab value (Grade 1B); mild cases may get hypertonic saline, oral hypertonic fluids or observation until urination (full text, checked 2026-09-29: Treatment, Table 6).

Practical Application

For a marathon, ultra or Ironman, plan to drink to thirst, not to a fixed schedule: the international consensus (Hew-Butler 2015, A-) attributes exercise-associated hyponatraemia — and all known deaths from it — to drinking more than you lose, and says salt or sports drink cannot protect someone who keeps overdrinking. Finishing heavier than you started, or not losing any weight over a long race, is the warning sign.
Sodium in drinks and gels has a role when drinking roughly matches losses in long events, but it is not a licence to drink more (Grade 1C; see REF-220, REF-223 for sodium planning).
Not from this paper's wording; the base's own practice built on its treatment section: during or after a long event, a worsening headache, nausea or vomiting, confusion or unusual drowsiness after drinking a lot mean medical attention now and no more water or sports drink until assessed — the assistant never advises drinking more to fix these symptoms. The statement itself says only that symptoms run from mild non-specific complaints to severe encephalopathy.
Treatment (hypertonic saline) is for medical staff; the athlete's job is prevention and early help.

Limitations

Consensus of experts over mostly observational data, case series and field studies; most recommendations are graded 1C (strong recommendation, low-quality evidence).
The hypovolaemic form of EAH in very long, hot events (ultras, hot Ironman races) remains debated in the statement itself; data on the contribution of sodium losses are limited.
The optimal number and spacing of aid stations and the effect of event-management strategies need further study.
How this entry was checked and changed
Why this level

the reference consensus on exercise-associated hyponatraemia (EAH); most recommendations are graded 1C (strong recommendation, low-quality evidence), a few 1A/1B, so the direction is firm while the underlying data are mostly observational and case series

Content correction 2026-09-27
2026-09-29: first added as a record-only pointer (no abstract exists). Rewritten the same day from the full text (publisher's version held by the Gettysburg College repository, cupola.gettysburg.edu/healthfac/66): definition, cause, risk factors, prevention (thirst, sodium, events) and treatment added with their grades; level C (pointer) -> A- (consensus).