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Dehydration While running: More Dangerous Than You May Think


  • In cases of prolonged dehydration, various muscular systems will begin to cramp, heart rate will increase, dizziness will occur due to lower blood pressure and the heart will be required to work harder than usual. If there’s no immediate fluid intake, the condition could potentially become life-threatening.
  • Runners should drink around 200cc of water one hour before setting out on a run. When running in hot conditions, which leads to increased perspiration levels, fluids should be taken on at regular 15-20 minute intervals.
  • Once a run is over, runners should replace the fluid loss by drinking fluids equal to the amount of weight which has been lost through sweat over the course of the run, as any weight loss will tend to be as a result of the loss of fluid in the form of perspiration.


During exercise, our body temperature rises, causing us to sweat more.  Some believe that the more you sweat, the better it is, because we’ll get slimmer quicker, which is mostly true. However, the fluid lost during exercise needs to be replaced, otherwise it could lead to dehydration which can be dangerous.

Dehydration refers to the continuous loss of perspiration or other bodily fluids without receiving timely fluid replacement, resulting in a dry mouth, concentrated urine, dizziness, cramps, and eventually the possibility of developing acute renal failure.

Warning signs of ‘dehydration’

  • Thirst and a dry mouth: As dehydration begins to set in, the body will respond with a dry mouth and feelings of thirst. Do not forget to always take a water bottle with you while on a run, being sure to sip water at regular intervals while running, or when you feel thirsty.
  • A decrease in running speed: You’ll notice that you may struggle to keep up to the steady pace of your group. No matter how hard you try, you’ll be unable to pick up your speed due to the muscle fatigue resulting from dehydration.
  • Urinating in small amounts and with a dark yellow color : Once a run is over, if you notice that you are urinating in small amounts, or that your urine is much darker than usual, this could be sign that your body has lost a lot of fluids which haven’t been sufficiently replaced.
  • Dizziness: Due to the drop in blood pressure because of dehydration, if fluids are not replaced, it could potentially lead to the person fainting.
  • An increased heart rate: The heart is required to work much harder than usual in order to respond to the drop in blood pressure, so you may notice that your heart rate is higher than usual.
  • The onset of cramp throughout various muscle groups: In cases of prolonged dehydration, various muscle groups will begin to cramp. If fluids are not taken immediately, it could potentially become life-threatening.

How should runners replace lost fluids?

  • Runners should drink around 200cc of fluids one hour before setting out on a run. This not just prevents dehydration, it also stops runners from needing the bathroom while out on a run.
  • For short runs, or on runs of less than an hour, runners should use drinking water to replace their lost fluids, drinking an amount which is roughly equal to the amount lost on the run.
  • On hot days where you are perspire more, greater amounts of fluids should be taken. These fluids should be sipped at regular 15-20 minutes intervals in order to prevent against a stitch that can result from drinking too much fluid in one go.
  • On runs of over an hour, runners should also take electrolytes to replace those lost through sweat. Electrolyte drinks should not contain more than 8% sugar. While ensuring that the right amount of fluids are taken, these drinks can also provide energy in the form of glucose, as well as minerals which can help to stave off fatigue and cramp.
  • When a run is over, runners should be drinking an amount of fluid equal to the weight of the fluids lost on the run. This is because any weight decrease after a run is mostly due to the fluids lost in the form of sweat.

Fluids to avoid before running

  • Carbonated drinks: Aside from the high sugar levels, the gas in these drinks play a major role in making runners feel uncomfortable with indigestion and gas.
  • Alcoholic drinks: Alcoholic beverages speed up dehydration, and cause accidents as a result of runners not being completely aware of what they’re doing.
  • Drinks containing coconut milk: Coconut milk is high in fat and low in carbohydrates, which could lead to runners feeling too full, thereby making these drinks unsuitable for consumption prior to a run.

Clean drinking water is the best form of fluid intake for a runner before setting out on a run. When running for over an hour, or when you feel that dehydration  setting in, low-sugar electrolyte beverages should also be consumed. It is also crucial that we remember to replace the fluids lost once run is over.

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