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Tuesday, 30 June 2015


Temperatures in the UK are today expected to tip 30 degrees, and it will be hotter over the coming days. There is a lot of advice being given in respect to how much to drink - and most of it is myth.

The ONLY time that you need to drink is if you are thirsty. Just drink to thirst and you'll be fine.

Drinking when you are NOT thirsty offers no advantage and can lead to water intoxication if taken to excess. The human body works best in perfect hydration balance, is designed to operate in a slightly dehydrated state, yet is NOT designed to operate in an over-hydrated state.

(All of these suggestions assume that you don't have an underlying medical condition of course - in which case seek medical advice particular to your condition.)

We get thirsty when our blood volume drops, or when the water balance between different compartments in our body is out of balance. This is the only time we need to drink.

STOP drinking when no longer thirsty. This allows your body to process the water that you have ingested. If you get thirsty some more, then drink some more. We should listen to our bodies.

We need to have a minimum fluid intake of about 1.75ltr a day to maintain water balance. This can come from food and/or drinking. From a hydration point of view you can get your fluid from water, coffee, tea, fruit juice, soup, milk...again it is a myth that you should avoid rehydrating with caffeinated drinks.

In hot weather we may need to drink more. Yet, drink to thirst - thirst is our body's signal we need hydration. At all other times we don't.


Start hydrated - the ACSM advises drinking 5-7ml of fluid per kg of body weight slowly at least four hours before exercise and allowing enough time for the excretion of excess water.

During exercise
we should only drink to thirst, and no more than 6-800ml per hour, ad libitum. Salts and electrolytes taken during exercise afford no advantage and can lead to physiological issues - ignore the marketing of sports drinks and supplement manufacturers.

In most training sessions up to one hour you may not even experience thirst, in which case don't drink. If you do experience thirst, and are training intensely, there may be benefit of taking a hypotonic or isotonic sports drink instead of just water.

Post exercise you need to drink around 1.2-1.5ltr per kg of weight lost during exercise. This is better sipped, and in small amounts, otherwise you'll throw your body out of balance, only at a speed you feel comfortable with, and drink in batches until no longer thirsty. A little sodium (salt) can aid in hydration at this time (increases urge to drink, improves palatability and promotes fluid retention) - although note we have electrolyte stores in our bodies and even an elite athlete will have enough from a single meal - there's no need to take salt tablets and electrolyte supplementation.

Salt tablets produce a very concentrated sodium solution in your stomach, delays stomach emptying and rehydration, as extra fluid must first be absorbed from your body into your stomach to dilute the solution.

Oh, a cheap and effective, perfect rehydration drink post exercise is skimmed milk!


For my friends who are fasting, if you are not drinking during the day it is strongly advised to ensure that you are properly hydrated before your fast. Take care on these hot days to keep yourself cool and not lose too much water in sweat. Note the post-exercise advice above.


This is a loss of thermoregulation - where our bodies can't lose heat fast enough and our core temperature rises above 40 degrees.

If you are not thirsty then it will not be due to dehydration. It is unlikely to be salt deficiency what with our modern diets. If suffering heat stroke seek medical attention - in the mean time take control of your environment - move somewhere cooler and take action to cool your body.


This is just a quick and general post, designed to give some simple understandings. The summary however is simple:

Drink when thirsty, and stop drinking when no longer thirsty.

Further Reading:

I have found the following books useful in understanding hydration:

Waterlogged by Tim Noakes
Human Physiology by Pocock, Richards and Richards
The Complete Guide to Sports Nutrition by Anita Bean

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