The Ultimate Guide to Hydration

The Ultimate Guide to Hydration

As most of us already know, the human body is made up of 80% water. It has a multitude of important roles including temperature control, brain function, immunity and muscle recovery. Being even slightly dehydrated (2%) can impair mental and physical performance! We lose fluids through sweat, urine, breathing and other processes which happen continuously. Therefore, rehydration must be tightly regulated to restore ’homeostasis’. The kidneys are the organ responsible for pulling the correct amount of water and minerals from our blood to replace the loses. Fluids and minerals are mainly sourced from the diet with very small amounts of minerals made within the body.

Hydration status is impacted most significantly by impacted by exercise and all environmental stressors (e.g. heat, immersion, gravity). Exercise generates heat in response to burning energy. In order to maintain internal temperatures conducive to life, we must use cooling mechanisms. One of the most important processes is cooling the skin via the sweat glands. Sweating is a physiological mechanism of heat dissipation that controls temperature maintenance. Sweat is composed of water and electrolytes (minerals). These may sound familiar: 

  • Sodium
  • Potassium
  • Magnesium
  • Phosphate
  • Calcium

Similarly, heat exposure through warm climates and heat therapy (e.g. sauna or steam) will activate a sweat response. Studies in athletes have shown that When matches take place in hot climates, athletes’ fluid losses increase by 150-200%, putting them at increased risk of heat-illness. It is common practice for these individuals to treat, or prevent, dehydration through well-structured fluid and electrolyte protocols when training in hotter climates or higher altitude.

Electrolytes are not only involved in fluid balance. They are very important at a cellular level to control electrical impulses within the nervous system. For example, heart beats, muscle contraction and blood volume. 

Role of electrolytes 

Sodium: Helps maintain blood volume and muscle contractions.

Potassium: Important for nervous system and muscle contractions.

Magnesium: Involved in metabolism, bone and muscle repair.

Phosphate: Key component of bone health, muscle contraction and energy production.

Calcium: Responsible for bone and teeth strength, nervous system functioning and enzyme


What is ‘Rehydrating’?

It’s widely accepted that water should be consumed to prevent and reverse symptoms of dehydration. These include dizziness, fainting, nausea and confusion. The importance of electrolytes on the other hand are commonly forgotten. There are mild-severe effects of ‘overhydrating’ or diluting the level of electrolytes in the blood. The same effects are observed when someone is severely dehydrated, with a higher level of electrolytes in their blood. Dehydration is a more common occurrence than ‘over-hydration’. Symptoms of dizziness and fainting should be monitored with proactive hydration plans, cold fluids during exercise and possible electrolyte supplementation.

A common method for assessing individual hydration requirements during exercise includes the subject, their water bottle and a weighing scale. Weighing the individual before and after training, subtracting the volume of fluid ingested and calculating their weight (kg) difference is a valid test for sweat rate. ‘Dehydration’ is any loses over 2-3% body weight. Additionally, urine colour charts (see below) or urine specific gravity (USG) measures can be used. Salt losses are equally important to measure. The quickest and most convenient method is by training in dark clothing. White stains on clothing indicate ‘salty sweaters’. 

Practical tips 

Fluid recommendations for the average individual is about 35ml fluid for every kg bodyweight. This means if you weight 70kg, you require 2.5L per day before taking ‘losses’ into account. If you notice that you sweat more than your friends and family during exercise, you might classify as a ‘heavy sweater’. Try one of the methods above to put that to the test! 1.25-1.5 L of fluid should be taken for every 1kg bodyweight lost during exercise. If you notice signs of dehydration (e.g. dark urine) before starting exercise, take 5-7ml fluid for every kg bodyweight 2-4 hours before. 

Rule of thumb: ingest 1-2L fluid for every 1 hr of moderate-intense exercise.

Added electrolytes (20-30 mmol/L sodium, 2-5 mmol/L potassium) will help retain ingested fluids and activate thirst response. Additionally, to test if you are a ‘salty sweater’, wear black to your workout and look out for white salt stains on your clothing. Salty sweaters should focus on replacing salt through food and drinks (see table). Don’t forget, over-hydration can be dangerous but more commonly a big inconvenience! No one wants to be running to the bathroom mid-sprint! 

Tip: The temperature and taste of the beverage may help with meeting your fluid requirements ad libitum. Prepare cold water bottles and/ or flavoured sports drinks instead of room-temperature water. 


General guideline for maintaining hydration when exercising are outlined below:

Before Training

2-3 hours before: 2 cups (500ml)

15m before: 1cup (240ml)

During Training Drink to thirst
After Training 1.5L for every kg lost


Electrolyte supplements

Although it is important to remember the importance of electrolytes, water is lost much quicker than electrolytes even during exercise and excessive sweating. It is possible to accurately measure sodium (salt) losses in sweat but this requires expensive, not readily-available equipment.

This personalised recommendation may be useful in elite athletes who rely heavily on their nutrition status to perform at their best. It’s not usually necessary for (most) recreational athletes who can rely on their ‘balanced’ diet and discretional supplements to provide their needs.

For reference most athletes’ sweat contains between 0.5-1.3g/L sodium lost anywhere between 0.2-3 L/hr. VITHIT have entered the market with their new, electrolyte-containing effervescent sachets!

VITHIT Effervescents

mg of sodium per sachet
The Great Defender 137
Hydration Station 160
Rocket Fuel 137


How will I know?

Our bodies are smart, as we know. When we begin to reach the tipping point of being well hydrated to hypo-hydrated (too little water in the body) (around 2% fluid loss), thirst mechanisms activate. We can rely on our thirst signals to drive our fluid needs (for the most part). Some circumstances like old age, certain medications, fatigue, underlying conditions can impair the effectiveness of this. Drinking protocol can be effective for some people, and in some sports requiring strict fluid intake. But the benefit of following a structure vs drinking to thirst is still up for debate. Goulet et al. explored the potential benefits of athletes drinking ad libitum vs following a prescribed hydration protocol. They found that indeed both methods support performance to a very similar extent despite athlete intake varying by approx. 500ml!

What’s to drink?

As mentioned, all fluids are included in hydration. That means you can count your morning coffee, smoothie, coke zero or orange juice towards your fluid intake. The only thing that doesn’t count is alcohol-containing drinks. Hydrating foods such as cucumber, melon, apples, tomatoes and celery also bring extra water into your system! Salty drinks and foods are a great way to replace electrolytes. Incorporate small amounts of pretzels, stock, salted nuts, olives, cheese or table salt (small dash) to your post-workout meal or snack.

Try out this recipe below for your at-home hydration mocktail. And don’t forget to try our latest, electrolyte-containing effervescent sachets! 

Hydration mocktail recipe: 

  • 2 tablespoons 100% tart cherry juice concentrate
  • 1 cups pure coconut water
  • 1 cups cold water
  • 2 key limes, juiced
  • 1/8 teaspoon salt


Ciara McNulty
CORU Registered Dietitian DI047525


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