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Hydration: Replacing electrolytes with sports drinks and others

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

Exercise depletes fluids and salts through sweating, breathing fast and hard, and making muscles work to their absolute maximum. There are so many products that go beyond plain old water, the choice can be bewildering, so what’s going to fuel your gym session or get you through your triathlon? Our pharmacist is here to cut through the big claims and let you know what’s behind the label.

Doctor’s advice

What’s the difference between rehydration drinks?

Every cell of your body needs electrolytes – salts such as sodium, potassium, magnesium, calcium, and chloride – and these are kept in a delicate balance. Exercise can disrupt this, causing you to lose salts, which need replacing. Water alone will just further dilute these salts, making your muscles feel more fatigued and making you feel worse.

Sports drinks are designed to deliver glucose, which can work as fuel in intense bouts of exercise, plus salts and water. They work best with short, sharp bursts of intense exercise. This glucose is burned up by the muscles, and this conserves energy stores kept in fat and liver glycogen.

Oral electrolyte solutions have a higher concentration of salts, replenishing stores and helping you to retain more water than a normal sports drink would. If you’re trying to lose weight, the added bonus is that they contain much less sugar than sports drinks.

Energy drinks give you a mental boost. They’re a source of sugar and water, plus stimulants like caffeine, which produce adrenaline to increase mental performance. This is great if you have an urgent deadline or some late-night studying, but it’s not going to improve your tennis game or the last miles of the marathon. It may even work against you in sports, as caffeine causes diuresis, making you pee water out and risking dehydration.

Which sports drink is right for me?

So, you’ve decided on a sports drink. There are three main types. Let’s talk through the science to work out which is right for you.

Isotonic drinks are the most popular as they’re a good all-around option. They have a combination of salts and sugar that matches the concentration in your body. They work best in prolonged or intense workouts, such as team sports or marathons, where you need an energy boost alongside topping up salt losses.

But isotonic drinks can cause a bit of bloating and tummy discomfort if taken in large quantities during a workout, as they’re not absorbed as easily as electrolyte-only drinks.

Hypotonic solutions are best for straight-forward hydration, where you don’t need to replenish glucose. These have a lower concentration of salts and sugar than the body, and therefore are suitable for sports such as gymnastics, sweating in hot climates, or diarrhea bugs. Most oral rehydration solutions or salts would be in this category.

Hypertonic solutions have a high concentration of salts and sugars, thereby giving a calorie kick to those recovering after high-intensity sports, and helping replenish glycogen stores of energy, getting you ready for the next session.

These drinks aren’t for me, any other options?

A randomized controlled trial in 2016 assessed the potential of other drinks to provide hydration. The study found that fluids such as orange juice or coconut water were just as good at hydrating subjects compared to sports drinks. Milk was also very good at hydrating and similar to oral rehydration salts.

So, when should I stick with water, and when should I upgrade?

Water should be your first port of call. Your body is well able to adapt to fluctuations in salts and glucose, changing the amount you pee or breathe out, how much is absorbed in the gut, and altering sodium and potassium from inside cells to outside. It keeps you in balance all day, every day.

So, you only need to consider special hydration products if you’re putting exceptional stress on your body, like high-intensity or prolonged exercise. For those working out for 45 minutes or less, or doing only mild to moderate intensity, water should do the job. Oral hydration salts might help in recovery afterward.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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