Hydration, hydration, hydration!

It’s only just over a month to the London Marathon and training is going really well.  I’ve had a couple of sports massages and completed a 20 mile run in 3 hours 47 minutes, so feel like I’m on track.  I’m planning to run 22 miles this weekend so need to make sure I’m well hydrated, especially if the weather stays unusually warm for this time of year.


Although water is not a nutrient as such, the maintenance of fluid balance is an important factor in physiological homeostasis. On average we get almost two thirds of our water from drinks and the remaining third from food. We lose water though skin, sweat, urine and faeces. Also our lungs must maintain a moist lining and so exhaled air always contains lots of water vapour.  Exercise makes us sweat which is our body’s way of trying to regulate and maintain a steady temperature and this can lead to dehydration.

My biology books say that a part of the brain (hypothalamus) contains receptor cells that are sensitive to the solute concentration of the blood.  When the concentration rises indicating that water loss is greater than intake, the hypothalamus responds in 2 ways:

  • It stimulates the thirst centre in the brain.
  • It stimulates the pituitary gland to produce anti-diuretic hormone (ADH), which acts on the kidneys to reduce the volume of urine.

That’s only part of the story, but that’s why we feel thirsty and the colour of our urine changes – fascinating!

Marathon training experts say that  during a long run an isotonic drink will help replace electrolytes such as sodium, potassium, which are minerals that are necessary for the body to function properly. These electrolytes must be replaced to keep the electrolyte concentrations of body fluids constant. So, many sports drinks have sodium chloride or potassium chloride added to them. You can also make your own using unsweetened fruit juice, water and a little pinch of salt.

I’ll be making sure I keep hydrated during my 22 mile run and over the next few days will be drinking a variety of herbal teas, water and fruit and vegetable juices, to keep my fluid levels topped up.

I made some delicious rainbow juice from beetroot, blueberries, spinach, celery, cucumber, carrot and orange. They are easy to make and kids love them. Just make three different coloured juices and poor them slowly over the back of a spoon.

Runners World has a really good article on hydration. This can be accessed via the following link:


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