When to Take Electrolytes: Before, During, After and Bedtime

Timing follows the loss, not the clock: take electrolytes during and after an hour or more of sweating, with a meal on a day you have eaten little, and in small sips through a stomach bug. In laboratory trials a salty drink had raised plasma volume by the time exercise began; what differs between drinks is how much water you still hold hours later. No trial has tested electrolytes before bed: check the label for caffeine and expect a bathroom trip. Part of the Wellgard electrolyte guide.

Evidence at a glance

• Trials: two pre-exercise sodium trials (21 trained athletes) and three rehydration trials (95 people), plus a sweat dataset of 506 athletes.
• Largest single trial: 72 men, 13 drinks, each drinking a litre of water and of three others, urine collected over four hours.
• Strongest measured outcome: after a concentrated sodium drink, 13 trained women cycled in 32 °C heat for 98.8 against 78.7 minutes to exhaustion; in 8 trained men plasma volume rose 4.5%.
• Not tested: electrolyte timing in everyday life, or electrolytes and sleep.

Sources checked on 13 October 2026.

When should you take electrolytes?

When you are losing them faster than meals put them back: an hour or more of sweating, a day of eating very little, or vomiting and diarrhoea. On an ordinary day with ordinary meals, water to thirst covers it; a measured drink is for the days that cost salt.

In 506 athletes, sweat carried about 0.8 g of sodium a litre at about 1.2 litres an hour, so an hour of hard sweating costs around a gram of sodium; sweat rates ranged from 0.26 to 5.73 litres an hour.¹

The NHS says around three quarters of the salt we eat comes from packaged and everyday foods, so missed meals are missed salt.² Electrolytes on a GLP-1 medicine covers that day.

With a stomach bug, the NHS advice is to "take small sips if you feel sick", and a pharmacist can recommend an oral rehydration solution; call 111 if you keep being sick and cannot keep fluid down.³ That sachet is a medicine: its amounts come from the leaflet or the pharmacist (rehydration sachets compared). No trial has compared morning with evening; the day decides the time. See also how many a day and the signs you need them.

Should you take electrolytes before, during or after exercise?

During and after, for sessions long or hot enough to cost salt. Before is about arriving ready, with ordinary meals and drinks behind you.

The American College of Sports Medicine position stand: before, when needed, drink at least several hours ahead so urine output can settle; during, avoid losing more than 2% of body weight as water, and drinks with electrolytes and carbohydrate "can provide benefits over water alone under certain circumstances"; after, replace the deficit. Weighing yourself before and after gives your own sweat rate.⁴

After exercise, sodium keeps the water in. In 12 men, six per drink, who had sweated off 2% of their body weight and drank the volume lost, a 61 mmol/L sodium drink left a median 260 ml of urine over 7.5 hours against 493 ml for 23 mmol/L; drinking more than the loss only helped with enough sodium.⁵ In 11 people, in a dairy-industry-funded trial, milk left 611 ml of urine over five hours against 1,184 ml after water and 1,205 ml after a sports drink.⁶ A review adds that carbohydrate, protein and food help too, so a salted meal after training counts.⁷

Before exercise, two small double-blind trials gave 8 trained male runners and 13 trained female cyclists about 757 and 628 ml of a drink with 164 or 10 mmol/L sodium, sipped over an hour from 105 minutes before exercise at 32 °C. On the salty drink the men's plasma volume rose 4.5% and they ran longer, whether they stopped at the core-temperature safety limit or at exhaustion; the women cycled 98.8 against 78.7 minutes.^{8, 9} The men's drink held about 2.8 g of sodium, more than the NHS daily maximum of 2.4 g for adults and about three hours of average sweat.^{10, 1} It is a research dose taken under supervision in a heat chamber, not a habit. Distances are in electrolytes before, during or after a run.

How long do electrolytes take to work?

Absorption is quick: after water and a sports drink, urine output jumped between one and two hours, so the fluid was already in.⁶ The difference between drinks shows over the next two to four hours, as how much you keep. "Working" means the water stays in rather than passing straight through.

In the heat-chamber trials, the drink was finished 45 minutes before exercise and plasma volume was already up.⁸ In a trial funded by a hydration research institute whose advisory board the lead author chaired, 72 hydrated, fasted men drank a litre of one of 13 drinks over 30 minutes. Over four hours they passed 1,337 g of urine after still water, against 1,038 g after an oral rehydration solution, 1,052 g after full-fat milk and 1,049 g after skimmed milk. Cola, diet cola, tea, coffee, lager, orange juice, sparkling water and a sports drink were no different from water.¹¹

Can you take electrolytes on an empty stomach, or with food?

Either works. The evidence leans towards food: a review of rehydration research found carbohydrate, protein and food taken with a drink help the body keep the fluid.⁷ On a day you have eaten little, a drink with a meal puts back salt the missed meals would have supplied.

If a drink unsettles your stomach, mix it at the volume the label gives and sip rather than gulp. The NHS lists stomach pain, feeling sick and diarrhoea among the effects of too much potassium, and diarrhoea from more than 400 mg of magnesium a day from supplements.¹⁰

Can you drink electrolytes before bed?

You can. No trial has tested electrolytes and sleep, for or against. Two things decide it: caffeine, and how much you drink late.

Some electrolyte drinks contain caffeine, and the NHS advice is plain: "Check the label for drinks that are high in caffeine."¹² In the 72-man trial, funded by a hydration research institute whose advisory board the lead author chaired, a litre of water drunk in half an hour by already hydrated men produced about 1.3 kg of urine within four hours, so a large drink at bedtime means a trip to the bathroom.¹¹ Magnesium and sleep is a separate question, covered in the Wellgard magnesium guide.

How do you mix electrolytes?

In the volume of water the label gives, stirred or shaken until fully dissolved; an effervescent tablet is ready once it stops fizzing. Powder, tablet or ready-made drink, the minerals per serving are what count, not the format.

Measure rather than guess: half the water doubles the strength, and the sodium counts towards your day either way. If you add creatine to the same bottle, no study has tested the combination; how to take creatine covers its timing. Milk, coconut water and sachets side by side: which drinks contain electrolytes.

What we don't know

• No trial has tested when to take electrolytes in everyday life, outside laboratory exercise.
• No trial has tested electrolyte drinks before bed or their effect on sleep.
• None of the retention trials tested a sugar-free electrolyte sachet.
• The two pre-exercise sodium trials enrolled 21 trained athletes in 32 °C heat; whether the result holds for everyday exercisers or in cool weather was not tested.

Frequently asked questions

Should you take electrolytes before or after a run?

For runs long or hot enough to need them, during and after; afterwards the sodium helps you keep the water.⁵ Distances and the weigh-yourself method are in the runners' guide.

Do electrolytes keep you awake?

Only if the drink contains caffeine, so check the label.¹² Otherwise no trial has tested it; the likelier wake-up is a full bladder.

How many times a day can you take electrolytes?

As often as your losses call for, at the amount the label gives, with the sodium counted. The NHS says adults should have no more than 6 g of salt a day, which is 2.4 g of sodium, and an hour of hard sweating costs about a gram of sodium on average, so a day of long sweaty sessions costs more than an office day.^{1, 2, 10}

Can you add electrolytes to any water?

Yes: tap, still or sparkling. In the 13-drink trial, funded by a hydration research institute whose advisory board the lead author chaired, sparkling water was no different from still water for urine output over four hours.¹¹

Can you take electrolytes if you have high blood pressure?

Ask your GP or pharmacist first. The sodium counts towards your day's salt, and sodium and potassium matter more with kidney disease, heart failure or medicines that hold either, such as ACE inhibitors, angiotensin receptor blockers, spironolactone and some diuretics. The NHS says older people should not take potassium supplements unless advised to by a doctor.^{2, 10}

Sources

1. Baker LB, et al. Journal of Sports Sciences, 2016. Observational dataset, 506 athletes; authors at a sports-drink maker's research institute. PubMed 26070030.
2. NHS. Salt in your diet. Page last reviewed 17 April 2023 (review overdue); checked 13 October 2026. nhs.uk.
3. NHS. Diarrhoea and vomiting. Page last reviewed 21 December 2023. nhs.uk.
4. Sawka MN, et al. Medicine and Science in Sports and Exercise, 2007. American College of Sports Medicine position statement. PubMed 17277604.
5. Shirreffs SM, et al. Medicine and Science in Sports and Exercise, 1996. Trial, 12 men (six per sodium drink), four sessions each; funding not checked. PubMed 8897383.
6. Shirreffs SM, et al. British Journal of Nutrition, 2007. Crossover trial, 11 people, four drinks; dairy-industry-funded. PubMed 17459189.
7. Evans GH, et al. Journal of Applied Physiology, 2017. Narrative review. PubMed 28126906.
8. Sims ST, et al. Medicine and Science in Sports and Exercise, 2007. Double-blind crossover trial, 8 men, single sessions; funding not checked. PubMed 17218894.
9. Sims ST, et al. Journal of Applied Physiology, 2007. Double-blind crossover trial, 13 women, single sessions; funding not checked. PubMed 17463297.
10. NHS. Vitamins and minerals: others. Page last reviewed 3 August 2020 (review overdue); checked 13 October 2026. nhs.uk.
11. Maughan RJ, et al. American Journal of Clinical Nutrition, 2016. Randomised crossover trial, 72 men, 4 hours per drink; funded by a hydration research institute whose advisory board the lead author chaired. PubMed 26702122.
12. NHS. Water, drinks and hydration. Page last reviewed 17 May 2023 (review overdue); checked 13 October 2026. nhs.uk.

General information, not medical advice: with kidney disease, heart failure, high blood pressure, medicines affecting sodium or potassium, or pregnancy, ask a pharmacist or your GP before using any electrolyte or rehydration product.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.