Euhydration is the state of optimal total body water content as regulated by the brain1.
We’re all aware that staying hydrated is important for maintaining a number of bodily functions, such as temperature regulation, blood pressure control, nutrient transportation, joint and disc lubrication, kidney and cognitive function. But how much fluid is enough, and is more, better?
The Scientific Advisory Committee on Nutrition (SACN) guidelines state that we should aim for 2 - 2.5 litres a day, depending on your sex and age; climate, health status and life stage are other factors which affect how much you need to drink - there are specific guidelines for growing children, pregnancy and older adults, who may have a greater risk of urinary tract infections. Water, tea, coffee, milk, as well as foods with a higher water content, such as fruits and vegetables, soups and smoothies, all count towards this quota. Alcohol does not (so don’t fool yourself!) and care should be taken regarding the dehydrating effects of both alcohol and caffeine (from coffee and tea as well as some sports drinks/gels).
However, a lot of people don’t reach this level of fluid intake. A good way to check is to take your glass/mug/water bottle, fill it up with water and pour it into a measuring jug; do this repeatedly for the number of mugs of tea/coffee/etc or glasses/bottles of water you drink. Then see how many litres you’re actually consuming (use the water to refill the kettle, water your garden/house plants or fill up your pet’s bowl, instead of pouring it away). Your urine should be pale straw in colour; darker urine is a sign you may need to drink more. Headaches can be a result of dehydration, as can constipation, and being dehydrated won’t help your blood pressure either. In addition, dehydration can often be confused with hunger, so drink more in order to see if you need to eat!
However, getting enough fluid is only one part of optimal hydration: balancing your blood salts, or electrolytes, is the other.
Electrolytes help us to retain the fluid we’re drinking. Sodium, potassium, calcium and magnesium are vital to control the balance of fluid inside and outside every cell in our body. We need this balance for muscle contraction and nerve transmission, kidney, heart and brain function, as well as maintaining blood pressure. Otherwise, you can feel dizzy, nauseous, unable to think clearly, have poor coordination, heart palpitations and suffer with muscle cramps.
During normal everyday activities, electrolyte balance should be quite easily achieved through normal diet – but what about the athletes and exercisers amongst us, as well as those working long hours in hot conditions? Sweating is a great way to lose heat from the body, especially during exercise and in hot temperatures, but you don’t want to lose too much sodium within it. Whilst there will also be small amounts of the other three electrolytes lost, sodium is by far the electrolyte which affects bodily functions and performance. Some people don’t sweat very efficiently – they barely sweat, so become hotter and redder, and can’t tolerate exercising in the heat (but their electrolyte levels are likely to remain consistent as a result). Whilst you can acclimatize to different conditions to a certain extent, how much water and electrolytes you lose on exertion, and how hydrated you remain, is largely genetically-driven.
Both sweat rate and how salty your sweat is, will dictate your hydration needs during exercise: if you sweat profusely and have white marks on your clothes or face, or you can taste salt on your skin, you’re probably losing a fair amount of sodium which needs replacing. ‘Good sweaters’ are those who sweat on exercise, but the hair follicles around their sweat glands filter the sodium back from the water lost ie. no white marks and their sweat isn’t too salty. As an aside, I recently read that licking yourself during exercise can help maintain electrolyte levels... Apart from looking rather odd, you’ll also be ingesting other waste products, so I wouldn’t recommend it!
Staying optimally hydrated.
First and foremost, it comes down to diet – whether you’re an athlete or not. On an every-day basis, drinking regularly throughout the day – with most of this coming from water – is the first step. And gaining your electrolytes from your diet should be easily achieved if you eat a varied diet based mainly around wholefoods. With the current health advice against salt, most people have stopped adding it to their cooking and food on the table. But it’s excess salt that's bad for you – the body can’t actually function without salt (some of you may remember the fable about the King’s daughter who, on being asked to give him the most precious gift, gave her father a bag of salt).
The main point here is to remember that we’re all different and so will have different salt needs – if we exercise regularly, if we sweat a lot, if we have high blood pressure or adrenal issues, and if we eat a diet high in processed foods (which typically have excess salt added) – and should follow advice appropriate to each of us. And adding salt yourself to food, rather than have salt already in it (eg. in ultra-processed foods or salted butter) means you have more control over how much salt you eat.
Your individual needs will then change depending on the type of physical activity you’re doing and the temperature/length of time you’re doing it. What you need during a gentle yoga session in a cool room will differ from doing a hard cycle ride or long hilly run in hot temperatures. So, if you’re going for a short stroll and it’s not particularly hot, you’re unlikely to need to carry your water bottle. Over-hydrating can be as much of a problem – you dilute your blood electrolytes causing the body to prompt you to pee, in an attempt to rebalance the electrolyte ratio within the blood, and you can become dehydrated as a result.
If you exercise regularly, the first thing is, again, to ensure your diet and hydration status is good at an everyday level first. Remember: ‘health feeds performance’2.
Then, you look at how long you’re training for: anything up to 60 minutes is unlikely to need further hydration, as long as you started the session fully hydrated (with electrolytes balanced) and you hydrate appropriately after. One way to gauge how much you need to rehydrate is based on weight loss, before and after exercise. It’s not an exact science, as it’s not all water lost during lengthy exercise sessions, but it will give you a good idea regarding your sweat rate.
You can have your sweat rate assessed professionally but this is rather costly. Really, it’s about trial and error during your training to see what hydration strategy works best for you, based on your individuality, fitness levels and climate. Precision Nutrition3 have some good resources, and some of their products may be especially helpful if you’re a salty sweater. Veloforte4 uses natural ingredients. I’ve also used Elete5 for a number of years – the ratio of sodium compared to the other electrolytes is slightly lower than in other products (I’m a sweater, but not too salty!) and the drops can be adjusted according to my needs at the time. It’s also tasteless in water, thus avoiding the often ‘cloying’ effects of excess sweetness in sports drinks and gels etc. Plus, if you get cramp, taking it directly onto the tongue can be really effective regarding cramp. However, I do not advocate this as something to do regularly: first it tastes like VERY salty water and second, it’s pretty harsh on the kidneys, so proactive action is always best. But I always carry it with me during longer races, as my ‘get out of jail’ card (and then reassess my hydration prep afterwards!).
And the issue with cramp is a tricky one. There is no consensus regarding why it happens, but it's likely to be a combination of dehydration/electrolyte imbalance, neuromuscular misfiring and lack of fitness for the physical activity undertaken. So aim to be fit, hydrated and trained well enough for the job in hand – whether it’s a race or a long afternoon doing heavy gardening in the sun!
Finally, just a brief point regarding the ‘sports drinks’ available to buy. Most of these never see a playing field, race or tournament, but the association with sport is strong. Gatorade was the first commercial sports drink, developed for the University of Florida’s football team, the ‘Gators’ and the recipe of water, sugars, salt and some flavouring is the basis of most sports drinks today – along with the addition of colourants, chemicals and stimulants (such as caffeine). However, the term sports drink seems to be interchangeable with energy drink, so you need to be careful to choose the one which suits your needs:
Hypertonic drinks: these have a carbohydrate content typically around 10%. Useful to provide ‘liquid energy’, but less effective for hydration as a result. Coke is a good example – have it towards the end of a race to avoid an energy (blood sugar) dump and ensure it’s flat!
Isotonic drinks: these are your typical commercial sports drinks (Gatorade, Lucozade, etc), and work to deliver fluid, electrolytes and energy in one drink. They have approximately 6% solution of carbohydrates as well as electrolytes. However, research has shown that a number of these have formulas/osmolarity which is actually hypertonic, so it’s best to drink some water alongside these to avoid gut issues and to aid hydration.
Hypotonic drinks: these are your hydration drinks (SIS, High 5, Veleoforte, Precision Hydration, Tailwind, Voom) - low in carbohydrates (up to 4%) and have a higher electrolyte level. Important when hydration is the priority, but often need bars/gels alsongside to provide energy. Dioralyte is a typical oral rehydration solution, as are specific sports products.
Alternatively, you can make your own sports drink: a 50:50 solution with fresh juice and water, then add a pinch of salt – no additives or chemicals, tastes better and cheaper too!
References
1. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train. 2017 Sep; 52(9): 877–895.
2. Craig, I. (2024), Centre for Integrative Sports Nutrition.