22 juin 2025

Hydration and electrolytes for vegetarian athletes: what the research shows

For almost every session under two hours in a temperate climate, drinking when you feel thirsty is enough, and tap water does the job. The one hydration accident that kills otherwise healthy athletes is not dehydration. It is exercise-associated hyponatraemia, caused by drinking beyond thirst. Advice of the sort “drink before you are thirsty, take a sip every ten minutes” comes straight from that misunderstanding.

The second point is less intuitive. Exercise-associated muscle cramps are not explained by losing salt or magnesium. In an ultra-trail race where runners were sampled before and after, those who cramped were no more dehydrated and no more sodium-depleted than the others. What set them apart was muscle damage markers two to three times higher, and far less regular strength training.

The third point is specific to a vegetarian diet. Sodium, potassium and magnesium are not the nutrients that become difficult when you drop meat. Potassium and magnesium are, if anything, better covered by a plant-based plate than by a meat-based one. The genuine concerns for a vegetarian athlete sit elsewhere: iron, vitamin B12, iodine and total energy intake.

Those three claims lead to the practical questions: how much sweat you actually lose, how to measure it at home in one session, when salt is worth adding and how much, which drinks hold up in controlled trials, and which signals mean stop.

What water and salts actually do during exercise

When you sweat, you lose water and dissolved salts, but not in the same proportion. Sweat is hypotonic relative to plasma, meaning it is more dilute than your blood. The sweat duct reabsorbs part of the sodium before the droplet reaches the skin, and how efficiently it does this varies a great deal between people.

The direct and counter-intuitive consequence is that sweating heavily without drinking concentrates the blood rather than diluting it. Plasma sodium rises, it does not fall. Thirst appears at that point, and it turns out to be a remarkably well-calibrated signal for that concentration. Drinking large volumes of plain water beyond thirst does the opposite: it dilutes plasma sodium and pulls the concentration down.

Extracellular sodium, intracellular potassium and magnesium each have a role in the excitability of muscle and nerve membranes. Those roles are real and well described in physiology. But having a physiological role says nothing about how likely a deficit is during a training session, or whether swallowing more of it helps. That leap is exactly what sports drink marketing makes, and it is the leap that most hydration guides made before it.

Exercise-associated hyponatraemia, the only fatal fluid risk in a healthy athlete

Exercise-associated hyponatraemia is defined as a blood sodium concentration below 135 mmol/L developing during exercise or within 24 hours of it. The 2017 review in Frontiers in Medicine is explicit about the cause: drinking beyond the dictates of thirst, combined with non-osmotic vasopressin release that stops the kidney clearing the excess, is the primary mechanism.

The orders of magnitude explain where the limit sits. An adult with normal renal function eating a Western diet can excrete between 500 and 1,000 mL of dilute urine per hour. Adding non-renal losses, sweat and insensible losses included, total clearance capacity reaches 1,000 to 1,500 mL per hour. Beyond that, water accumulates. That is why “a sip every ten minutes whatever happens” becomes dangerous the moment somebody with a low sweat rate follows it literally over a long duration.

A field review published in 2025 in Open Access Journal of Sports Medicine went through 56 field studies and 220 cases of hyponatraemia across seven outdoor endurance activities lasting 5 to 29.5 hours. Its findings are worth knowing:

A greater percentage of women were affected than men, though not the greater absolute number.
The absolute plasma sodium value is not a reliable predictor of clinical severity.
Running and hiking produced far more cases than cycling, swimming or triathlon.
The most common mild complaints were nausea, weakness or lethargy, dizziness, headache and swelling of the extremities.
Moderate-to-severe signs were altered mental status, vomiting, seizure, agitation, collapse and loss of consciousness.

The item that deserves attention is that swelling of fingers, hands or ankles. It is a sign of water excess, and it appears in somebody who feels they are doing everything right. A ring that gets tight late in a long event, together with nausea and a headache, means stop drinking, not drink more.

Taking salt does not reliably protect against this. A study on a 161 km ultramarathon found that hyponatraemia, muscle cramping, dehydration and nausea were all unrelated to participants’ total sodium intake. A published case report documented symptomatic hyponatraemia despite oral sodium supplementation. What protects you is not drinking to excess.

The practical conclusion of the 2017 review is stated plainly: drinking according to the dictates of thirst, during and immediately after exercise, prevents exercise-associated hyponatraemia when the exercise is performed in a temperate climate and lasts less than 17 hours.

What that means for an ordinary session

A 45-minute run, an hour of bike commuting, a yoga class, a gym strength session: thirst is enough, and there is no reason to leave home with a numerical plan. The question becomes legitimate beyond two to three hours of continuous effort, in serious heat, or in a race where you sweat heavily and have continuous access to drink stations.

Cramps almost never come from electrolytes

This is the most firmly established belief in sports nutrition, and the one field data contradicts most bluntly.

A 2026 study in the Journal of Strength and Conditioning Research followed 58 finishers across two editions of the same ultra-trail race, with blood and urine sampling and body mass measured before and after. Nine runners, 16%, had exercise-associated muscle cramps diagnosed immediately after finishing. The results:

Body mass change did not differ between crampers and non-crampers.
Post-race urine specific gravity did not differ.
Post-race serum sodium did not differ.
Post-race potassium was in fact higher in crampers (5.04 versus 4.66 mmol/L).
Creatine kinase at 24 hours was 5,166 versus 1,940 U/L, and at 48 hours 3,194 versus 894 U/L.
Lactate dehydrogenase followed the same pattern at both time points.
55.6% of crampers did regular lower-limb strength training, against 87.5% of non-crampers.

In other words, the crampers were neither more dehydrated nor more sodium-depleted. They had more muscle damage and had trained their legs less. That fits the altered neuromuscular control theory: fatigue disturbs the balance between excitatory input from muscle spindles and inhibitory feedback from Golgi tendon organs, and the muscle locks into involuntary contraction.

A 2026 systematic review with meta-analysis in the International Dental Journal, covering 13 randomised trials, reaches consistent conclusions on supplementation. Magnesium reduces the frequency of pregnancy-related cramps (4 trials, roughly 364 participants, pooled risk ratio 1.35, 95% CI 1.05 to 1.74). For nocturnal or persistent cramps in adults (4 trials, roughly 396 participants) the effect is not significant: mean difference of -0.42 cramps per week, 95% CI -1.15 to 0.31. The authors conclude that calcium and potassium remain unsupported by the data, and that sodium-based interventions are context-specific.

What still stands up in practice if you cramp regularly: stretch the muscle during the episode, which remains the most effective measure; narrow the gap between race intensity and training intensity; and strengthen the muscles involved, which was the one factor that clearly separated the two groups in the ultra-trail study. Swallowing magnesium before every outing has no basis for this purpose.

How much you really sweat, and how to find out

Most hydration advice rests on a sweat estimate nobody ever measured. Sweat rate and sodium concentration vary enormously with the individual, the intensity and the climate.

A cross-sectional study published in Nutrients in 2026, on 285 Chinese adults under controlled temperate conditions, gives usable orders of magnitude. Mean sweat rate was 0.71 L/h and mean body mass loss 0.78%. Running produced higher values (0.92 L/h, 1.16% mass lost) than brisk walking or cycling. Whole-body sweat sodium concentration averaged 34.1 mmol/L, with 59.3% of participants in the moderate 30 to 60 mmol/L band. Men sweated more and lost more sodium; women showed higher potassium, zinc and copper.

A second study, published in Physiological Reports in 2026 on 15 trained athletes, shows sweat sodium rising with intensity: 44.5 mmol/L at low intensity, 54.9 at moderate, 61.3 at high. A third, also in Nutrients in 2026, on eight highly trained cyclists across two five-hour sessions at 30 °C, shows that an individual’s sweat sodium concentration varies only trivially between sessions and can be predicted with good precision from a single sample taken at 40 minutes.

Two sentences summarise the practical reading. Your own sweat is relatively stable and therefore worth measuring once. But it may sit a long way from the average, and no generic recommendation can guess it for you.

The weigh-in, in practice

This is the one useful measurement you can make without equipment, and it costs you one session.

Empty your bladder, then weigh yourself naked before the session on a scale accurate to 100 g.
Do your usual session, recording exactly how much you drink, in millilitres.
Towel off, remove soaked clothing, weigh yourself naked again without having been to the toilet.
Sweat loss in litres = mass lost in kilos + volume drunk in litres.
Divide by duration in hours to get your hourly rate.

An example: 71.4 kg before, 70.5 kg after, 500 mL drunk over 1 hour 15. Total loss = 0.9 + 0.5 = 1.4 L, so roughly 1.1 L/h. Repeat it in hot and in cold weather; the gap is often twofold.

The number is not there to let you programme intake minute by minute, which would take you straight back to the original problem. It tells you whether you are somebody who loses 0.4 L/h, in which case salt will never be a question, or somebody who loses 1.8 L/h, in which case a long summer outing needs real preparation.

When salt becomes useful, and how much

A litre of sweat at 40 mmol/L of sodium carries away roughly 0.9 g of sodium, about 2.3 g of table salt. An hour of moderate sweating therefore costs something like 0.5 to 1 g of salt. That is small against ordinary dietary intake: the global mean for adults was 4,278 mg of sodium per day in 2021 according to the WHO, equivalent to about 11 g of salt, more than double the recommended threshold of less than 2,000 mg of sodium a day.

That contrast is why most recreational athletes need no added salt at all. The next meal covers the loss without anybody thinking about it.

Salt becomes a real subject in three specific situations:

Continuous effort over three hours, particularly in heat, where cumulative losses reach several grams.
A measured high sweat rate, above roughly 1.5 L/h, combined with visibly salty sweat: white marks on skin and clothing, sweat that stings the eyes.
A diet that is already very low in salt, which happens when you cook everything from scratch without salting and avoid processed food. A sustained reduction in sodium intake lowers your baseline plasma sodium, including before exercise.

When salt is justified, the useful amount is modest: roughly 300 to 700 mg of sodium per litre of drink, which is about 0.8 to 1.8 g of salt per litre. Beyond that the drink turns unpleasant and adds nothing. A pinch of salt in a half-litre bottle, with a little sugar for taste and absorption, reproduces cheaply what the industry sells.

Two cautions. Sea salt, Himalayan pink salt and table salt deliver essentially the same thing: sodium chloride. The trace minerals that justify the price difference have no nutritional weight at culinary doses. And if you are salting more for sport, the WHO separately recommends that all salt consumed should be iodised, which matters particularly in a vegetarian diet where iodine is already a weak point. Iodine on a vegetarian plate deserves treating on its own terms.

Finally, high blood pressure, kidney failure, heart failure or diuretic treatment change the equation completely. In those situations, adjusting salt and water is a matter for your doctor, not a general article.

What so-called natural drinks are actually worth

Coconut water is presented everywhere as the ideal recovery drink. The measured data are more nuanced than the marketing.

According to the USDA composition table, 100 mL of coconut water provides roughly 250 mg of potassium, 105 mg of sodium, 25 mg of magnesium, 24 mg of calcium and 3.7 g of carbohydrate, for 19 kcal. In millimolar terms sodium sits around 45 mmol/L and potassium around 64 mmol/L. The profile is therefore the inverse of sweat, which is sodium-rich and potassium-poor.

Controlled trials give three converging results. A randomised crossover trial published in 2026 in the Journal of Strength and Conditioning Research, on 8 recreational athletes dehydrated by 1.36% of body mass then rehydrated to 150% of the loss, compared flavoured water, coconut water and a commercial carbohydrate-electrolyte drink. Flavoured water produced markedly greater urine output (530 mL against 170 mL for the other two). Coconut water therefore proved as effective and as palatable as the commercial drink, despite its lower sodium concentration.

A triple-blind crossover trial published in 2026 in the International Journal of Sport Nutrition and Exercise Metabolism, on 12 participants cycling for an hour at around 33 °C, compared water, a sodium-potassium drink and coconut water. No significant difference between hydration strategies on thermal strain, fatigue, heart rate, body mass or inflammation, once fluid intake was controlled.

Finally, the systematic review published in 2025 in the Journal of Athletic Training, part II, compared alternatives to carbohydrate-electrolyte drinks. On coconut water, three trials showed no difference against plain water at multiple time points. Skimmed or low-fat cow’s milk, by contrast, improved volume status compared with water in four studies, at a certainty of evidence the authors themselves describe as very low.

The honest summary runs like this. Coconut water is a pleasant, sensibly composed drink, worth roughly what a sports drink is worth, which is roughly what water is worth in most situations. It deserves neither its miracle status nor its price per litre. If you enjoy it, drink it. If you expect a measurable effect on recovery from an ordinary session, you will be disappointed.

For rehydration after a heavy session, what matters more than mineral content is the presence of solutes that slow renal clearance. A 2024 study in the same journal, on 16 participants dehydrated by 2%, showed fluid retention of around 69% with skimmed lactose-free milk against roughly 40% with water, over a three-hour follow-up. A 2026 trial on a milk permeate drink with high osmolality points the same way. Milk is not a drink for during exercise, it sits too heavily, but it is an effective recovery drink for anyone who consumes dairy.

Potassium and magnesium on a vegetarian plate

This is where the ambient worry is most disproportionate. Potassium and magnesium are abundant in exactly the foods a vegetarian diet places at the centre.

The NHS gives 3,500 mg of potassium a day for adults aged 19 to 64, and 300 mg of magnesium for men and 270 mg for women. Some measured values, per 100 g, from the USDA table:

Food	Potassium	Magnesium	Sodium
Raw spinach	558 mg	79 mg	79 mg
Baked potato, flesh and skin	535 mg	28 mg	10 mg
Raw banana	358 mg	27 mg	1 mg
Coconut water	250 mg	25 mg	105 mg

A plate with 200 g of potatoes, 100 g of green vegetables and a banana already reaches roughly 1,700 mg of potassium, close to half the daily reference, before counting pulses, nuts and wholegrains. Pulses and nuts do the same work for magnesium. Pumpkin seeds, almonds, buckwheat, quinoa and dark chocolate carry the highest densities at realistic portion sizes.

The banana obsession deserves some perspective too: at 358 mg per 100 g, an average 120 g banana provides about 430 mg of potassium, which is good without being exceptional. A portion of potatoes provides more. So do spinach, chard and white beans.

If you want to work on these intakes seriously, the page on calcium and magnesium without dairy goes through the portions in detail.

The genuine concerns for a vegetarian athlete

They are not about electrolytes.

Iron is the most frequently cited issue, and the position is more nuanced than the usual telling. A narrative review published in Current Nutrition Reports in 2026 concludes that available studies do not consistently show a higher prevalence of iron deficiency among vegetarian athletes compared with omnivores. Despite lower bioavailability of non-haem iron, total dietary iron intake in vegetarians often equals or exceeds that of omnivores, and several adaptive mechanisms, including improved absorption efficiency, help preserve iron balance. The authors also note the methodological heterogeneity of the studies and the limited inclusion of elite and female athletes, which constrains their conclusion. Blood monitoring therefore remains sensible in menstruating women, distance runners and during heavy training blocks. The practical levers are set out on the page about plant-based iron absorption.

Vitamin B12 is the one nutrient for which a supplemented source is necessary on a vegan diet, and often useful on a strict lacto-ovo pattern where animal products are eaten sparingly. It is non-negotiable and covered in detail on the vitamin B12 page.

Iodine is the least well covered nutrient in plant-based diets in Switzerland, given the absence of fish and, in some patterns, dairy.

Total energy intake is the most frequent and least visible shortfall of all. A plant-based plate is bulky and filling at equal calories, an advantage day to day and a handicap when training load climbs. Low energy availability disrupts hormones, bone density and recovery long before any electrolyte becomes an issue. The plant protein guide and the page on diet and endurance sport tackle this head-on.

Three homemade drinks that hold up

None of these recipes is essential. They earn their place when duration or heat justify a combined intake of water, carbohydrate and sodium, and when plain water stops going down because it becomes cloying.

Lemon and salt sports drink, for a long outing

Per litre:

900 mL water
100 mL freshly squeezed lemon or orange juice
30 to 60 g sugar or maple syrup
1.5 g iodised salt, roughly a level quarter teaspoon

That gives about 30 to 60 g of carbohydrate and around 600 mg of sodium per litre, which sits in the useful band. The sugar is not only for taste: carbohydrate and sodium share an intestinal transporter, and having both present speeds up water absorption.

Coconut water recovery drink

For 400 mL:

250 mL coconut water
100 mL water
1 ripe banana
1 teaspoon almond butter
1 pinch of salt

Roughly 800 mg of potassium, plus carbohydrate and protein that make it more of a liquid snack than a drink. Useful after a hard session when your appetite for solid food has not come back.

Iced hibiscus and ginger infusion, with no functional claim

Per litre:

1 litre boiling water
2 tablespoons dried hibiscus flowers
15 g fresh grated ginger

Steep for 10 minutes, strain, chill. No demonstrated effect on performance or recovery, but a refreshing drink that helps you take in enough fluid across a hot day when plain water gets tedious. That is reason enough. The page on 24-hour hydration offers other variations.

Before, during, after: what is supported and what is not

Before exercise, arriving normally hydrated is enough. Drinking half a litre two hours ahead, as you often read, does no harm but has no demonstrated benefit for somebody who drinks normally through the day. Loading up on water just before the start is actively counterproductive: you will set off with a full bladder and an already lowered plasma sodium.

During exercise, the useful rule is thirst. Under an hour, water alone does the job in nearly every case. Between one and three hours, a carbohydrate drink becomes worthwhile for energy, which is not a hydration question. Beyond three hours or in serious heat, adding sodium becomes reasonable, and knowing your own sweat rate starts to pay.

After exercise, if the loss was substantial, drinking roughly 1.25 to 1.5 times the volume lost over the following hours compensates for the urine you will produce. This is where drink composition matters most, with the documented advantage of skimmed milk over plain water in terms of retention. Eating a normal, salted meal with water-rich foods does the same job for most people with no arithmetic at all.

The idea of a thirty-minute metabolic window after which everything is lost does not survive recent data. It was built on fasted protocols and on repeated efforts within the same day. If your next session is tomorrow, there is no urgency.

Warning signs and what to do

The NHS lists the symptoms of dehydration in adults and children: feeling thirsty, headache and light-headedness, dark yellow strong-smelling urine, urinating less often than usual, dizziness, tiredness, a dry mouth, lips and tongue, and sunken eyes.

The NHS also distinguishes heat exhaustion, which does not usually need emergency help if the person cools down within 30 minutes, from heatstroke, which is an emergency. Heat exhaustion shows as tiredness, dizziness, headache, nausea or vomiting, excessive sweating with pale clammy skin, cramps in the arms, legs and stomach, a high temperature, intense thirst and irritability. The recommended response is to move the person somewhere cool, remove unnecessary clothing, give plenty to drink including an isotonic sports drink or oral rehydration solution, cool the skin by spraying or sponging with cool water while fanning, and place cold packs wrapped in cloth under the armpits or on the neck. They should feel better within 30 minutes.

Signs of heatstroke mean calling emergency services immediately: a very high temperature, hot skin that is not sweating, fast breathing and a fast heartbeat, confusion and restlessness, a seizure, loss of consciousness.

The picture not to confuse with dehydration is hyponatraemia: nausea, weakness, dizziness, headache and above all swelling of the hands or ankles, in somebody who has drunk a lot and has not lost weight or has gained it. Here, giving more fluid makes things worse. The distinction rests on the drinking history and on body weight, not on any single symptom.

Six common mistakes

Following a fixed hourly drinking schedule regardless of heat, intensity and actual sweating. That is the direct mechanism of exercise-associated hyponatraemia.
Treating a cramp with magnesium or salt, when the field data point towards neuromuscular fatigue and a strength training gap.
Paying three francs for half a litre of coconut water in expectation of an effect controlled trials do not show.
Reading urine colour just after drinking a large volume: it will be pale whatever your actual hydration state, because the kidney clears the surplus straight away.
Cutting salt out of the daily diet entirely with good intentions, when a sustained reduction lowers your baseline plasma sodium and complicates long efforts.
Looking for performance in electrolytes when the real shortfall is in total energy intake, iron or B12.

Adapting to the situation

Indoor training, under an hour, temperate climate: a water bottle, drunk to thirst. Nothing else is justified.

Running for one to two hours: water, plus carbohydrate if the effort is hard or you started fasted. Salt is only useful if you have measured a high sweat rate.

Ultra, long mountain hiking, endurance cycling: this is where the question becomes serious in both directions. Know your sweat rate, plan for sodium, and above all never drink beyond thirst. Hiking and running are the two activities that produce the most hyponatraemia cases according to the 2025 review. At this format, solid fuelling matters more than the drink, and the page on planning a menu for endurance athletes covers that side.

Heat or heatwave: sweat rate can double. Shifting the session’s time of day matters more than any drink. The page on no-cook meals during heatwaves covers the rest of the day.

Pregnancy, hypertension, kidney or heart disease, diuretic treatment, SSRI antidepressants: these situations change water and sodium handling, and some medications raise hyponatraemia risk. Adjustment belongs with a health professional.

What changes in Switzerland

Two local particularities are worth noting. Tap water is drinkable across the whole country and the FSVO recommendations name it first, which makes buying bottled water for sport unnecessary. And Swiss mineral waters differ enormously in mineral content: between a very low-mineral water and one rich in sulphate or magnesium there is a factor of more than ten. If you buy a mineral water for its magnesium, read the analysis on the label rather than the marketing copy.

Mountain sport adds altitude to the picture. At altitude, respiratory water losses rise because the air is dry, thirst is often perceived less clearly, and access to water along the route is limited. This is one of the few cases where paying deliberate attention to your drinking is sensible, without letting it harden into a fixed schedule.

Winter sport creates the opposite trap. Cold blunts thirst, the sweat evaporates invisibly under technical layers, and heavy clothing plus a rucksack push the workload up. Sweat rates on a ski touring day are frequently comparable to a summer run, while the perceived need to drink is far lower. Here the risk really is under-drinking, not over-drinking, which is the reverse of the summer marathon situation.

Limits of the available data

The sweat rate and sweat composition data come from specific populations and conditions, often young trained adults in laboratories. They give orders of magnitude, not your personal value, which only the weigh-in will give you.

The ultra-trail cramp study covers 58 finishers of whom 9 cramped, which is few. It is consistent with the wider literature, but a sample that size does not close a debate on its own.

The coconut water trials had 8 and 12 participants. That is enough to show the absence of a clear superiority, not enough to rule out a small effect.

Nothing here replaces medical advice, and none of it applies to children, older people or clinical situations, where thresholds and risks differ.

Frequently asked questions

Should I drink before I feel thirsty? Not during exercise. That is precisely the instruction that causes exercise-associated hyponatraemia. Thirst is a well-calibrated signal for plasma concentration. During an ordinary day, drinking regularly is sensible because the signal is less exercised and people forget, but that is a different situation.

How much water per day? The Swiss dietary recommendations from the FSVO give 1 to 2 litres of unsweetened drinks per day, favouring tap water, mineral water and herbal or fruit teas. Caffeinated drinks count too, in moderation. On top of that comes the water in food, and for an athlete the volume lost as sweat.

Does coffee dehydrate you? Not at usual doses. The FSVO explicitly counts caffeinated drinks towards fluid intake. The diuretic effect exists but stays modest in regular consumers. The subject is covered on the page about coffee and sports nutrition.

Are commercial isotonic drinks worth anything? They are useful beyond two to three hours of effort, essentially for their carbohydrate. Below that they supply calories you do not need. You can reproduce the same thing with water, sugar, citrus juice and a pinch of salt.

Does magnesium-rich mineral water replace a supplement? Some mineral waters carry meaningful amounts of magnesium and calcium, which is a convenient contribution rather than a treatment. Compare labels rather than slogans: contents vary tenfold between brands.

Do I need salt tablets for a marathon? Nothing indicates it in the general case. The data show that total sodium intake was unrelated to hyponatraemia, cramping or dehydration among participants in a 161 km ultramarathon. If you lose a lot of salty sweat, a little sodium in the drink is enough and is dosed more finely than a tablet.

How do I know if I am well hydrated day to day? Urine colour on waking is a crude but usable indicator, provided you do not read it just after drinking. Stable weight from one day to the next, normal thirst and the absence of unexplained fatigue tell you more than any isolated measurement.