Electrolytes for Hyponatremia

The short answer is no. In a randomised trial at the Cape Town Ironman, triathletes who took salt tablets swallowed an extra 3.6 g of sodium, yet finished with the same serum sodium and weight change as those on placebo or nothing [1]. In a desert ultramarathon study of 266 runners, neither the rate nor the total of supplemental sodium was linked to hyponatremia [2], and in the Boston Marathon, weight gain raised the odds 4.2-fold while the type of fluid people drank made no difference [3].

Electrolytes are not useless: sodium in a drink slowed the fall in plasma sodium compared with water in several lab trials [4, 5]. But when women drank 1 L an hour for 4 hours, 46% still became hyponatremic on the saltiest drink [4]. The protection that works is not drinking more than you lose [6].

In 2,135 weighed athletes, post-race sodium fell in a straight line as body weight rose, and weight gain from drinking too much was the main cause of low sodium [6]. The same analysis found that the athletes who developed it also retained the extra water, because vasopressin (antidiuretic hormone) was not adequately suppressed. A 2026 review agrees that excess fluid and vasopressin drive the condition, and that sweat sodium loss plays a less important role [7].

Sodium in a drink offsets only part of the dilution. A typical sports drink holds about 20 mmol/L of sodium [8], while hyponatremia is defined as blood sodium below 135 mmol/L [9]. Drinking large volumes of a fluid that dilute still adds more water than salt.

When athletes drink only enough to replace heavy sweat losses in the heat, sodium makes a measurable difference. Replacing sweat with distilled water lowered plasma sodium 2.48 mmol/L per hour versus 0.86 with an 18 mmol/L sports drink, and one man fell to 128 mmol/L on water [10]. A 60 mmol/L drink kept plasma sodium and volume steadier than a 21 mmol/L one over 3 hours at 34 °C [8].

These are small shifts in lab volunteers who did not become ill. Hyponatremia also appears in dehydrated runners: in 161-km races in northern California, 35.6% of those with it had lost more than 3% of body weight [11]. The mechanism doesn't tell you how much salt any one athlete needs, and the field studies show salt supplements did not separate who got sick [12].

No electrolyte dose has been shown to prevent hyponatremia. Salt tablets taken at a suggested 1-4 an hour (620 mg each) made no difference in the Ironman trial [1]. A 2026 review recommends drinking when thirsty instead of drinking ahead of thirst [7], and tracking intake and losses so you don't gain weight; sodium and heat acclimatisation may help attenuate declines in sodium [13].

If you sweat heavily in long, hot sessions and drink to replace those losses, a sodium-containing drink keeps blood sodium steadier than plain water [5, 8]. For general rehydration targets, see electrolytes for hydration. Treatment is different: concentrated 3% saline, given by medical staff, reversed mild-to-moderate symptoms in a randomised trial [14].

The only large randomised trial gave 413 Ironman finishers salt tablets, starch placebo or nothing; serum sodium, weight change and finishing time did not differ, and the authors concluded supplementation was not necessary [1]. In 13 women drinking 1 L an hour for 4 hours, plasma sodium fell 2.5 mmol/L on a 680 mg/L sodium drink versus 6.2 mmol/L on water (p < 0.001), but mild hyponatraemia still hit 46%, 69% and 92% on high-sodium, low-sodium and water trials, and the fall tracked weight change [4].

When men drank only enough to match sweat loss at 30 °C, serum sodium ended at 137.3 and 136.7 mmol/L with sodium drinks versus 134.5 and 134.4 mmol/L with the waters (P < .05) [5]. These trials show that sodium shifts the numbers; they do not show it prevents illness in athletes who overdrink.

At the 161-km Western States race, 93.9% of runners used sodium supplements; the 6.6% who became hyponatremic took salt at the same rate as the rest, and the authors judged low salt intake to have minimal responsibility [12]. In desert ultramarathons, supplemental sodium neither prevented hyponatremia nor caused the high sodium seen in 17.2% of runners [2]. In the Boston Marathon, 13% of 488 runners finished hyponatremic and 0.6% critically so; composition of fluids ingested was not associated [3].

A case report shows the limit plainly: a runner with previous hyponatremia took more than 6,500 mg of sodium on advice, drank 9.2-10.6 L of water over 17 hours, and still reached 122 mEq/L [15]. An international consensus panel calls exercise-associated hyponatremia a preventable and treatable fluid imbalance [16].

For athletes with mild-to-moderate symptoms, a bolus of oral 3% saline led to discharge after 50.3 minutes versus 75.8 minutes for IV saline (P = 0.02) in a 20-person trial [14]. In an 8-runner pilot of asymptomatic cases, the same 100 mL dose raised sodium only when given IV [17]. Guidelines stress telling it apart from heat exhaustion and heat stroke, which look similar [9].

Outside sport, hyponatremia usually has a medical cause. In the syndrome of inappropriate antidiuresis, management includes fluid restriction, salt tablets and medicines [18], but in a 92-patient trial, 3 g/day of salt plus furosemide added nothing to fluid restriction alone [19]. In cholera, reduced-osmolarity oral rehydration solution raised the risk of biochemical hyponatremia compared with standard solution (RR 1.67) [20]; see oral rehydration for diarrhoea.

Exercise-associated hyponatremia is defined as blood sodium below 135 mmol/L during or up to 24 hours after prolonged activity, and severe cases need rapid recognition and treatment [9]. Symptoms range from nausea, vomiting and headache to confusion, coma and death; life-threatening cases need intravenous 3% saline [7]. Relying on salt tablets can give false reassurance, as the case of a runner who took over 6,500 mg of sodium shows [15].

Too much sodium is not harmless either: in hot 161-km races, researchers judged excessive sodium supplementation and drinking beyond thirst ill advised [11]. Low sodium found on a blood test outside sport needs a diagnosis, not an electrolyte drink. For cramps, see electrolytes for muscle cramps.

Medicines that affect water and salt handling change the picture. In the SIAD trial, furosemide raised the rate of acute kidney injury and low potassium without speeding sodium correction [19]. Non-steroidal anti-inflammatory drugs are a smaller risk factor in one review [13], but were not associated with hyponatremia in the Boston Marathon [3]. If you have been told to restrict fluid or take salt tablets for a medical reason, follow that plan rather than sports guidance; see electrolyte supplements for product types.