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Brain Hydration

Posted Jul 01 2009 1:46pm
By Gregory Kellett, a cognitive neuroscience researcher at SFSU and UCSF, and science writer for Lumos Labs.

Your brain is made up of 60% water and many of us may not be drinking enough of the clear wet stuff to keep our thinking “juicy.”

Not drinking enough water has detrimental effects on our brains. When your body lacks water, brain cells and other neurons shrink and biochemical processes involved in cellular communication slow. A drop of as little as 1 to 2% of fluid levels can result in slower processing speeds, impaired short-term memory, tweaked visual tracking and deficits in attention.

With proper hydration however, neurons work best and are capable of reacting faster.

What constitutes proper hydration is controversial. Some say that it is important to imbibe 8 tall glasses of water daily, while others claim that one should only drink when thirsty.

In fact, there is no one golden rule to staying well hydrated. The amount of water each of us needs varies from person to person as it depends on each individual’s physiology and lifestyle activities like diet and exercise.

Experiment and see what feels good. In today’s world of infinite distractions however, it is best not to leave hydration to your sense of thirst alone. It is also important to note that your ability to notice thirst typically diminishes with age.

Also of note:

  • Sweating from exercise or high temperatures can result in more than 3 liters an hour of fluid loss.
  • The maximum amount of water the body is capable of absorbing is 1 liter an hour or 330 milliliters every 20 min (the ideal amount to drink under high sweat conditions).
  • Although good for energy, foods high in protein and sugar increase the body’s need for water.


Drinking too much water is very dangerous! Over-hydration causes a sodium imbalance that can be fatal. It is common for marathon runners to be hospitalized because of overzealous hydration during the race.

Approach fluid consumption with moderation.


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Kleiner, S. M. (1999). Water: an essential but overlooked nutrient. Journal of the American Dietetic Association, 99(2), 200-6.

Lang, F., Busch, G. L., Ritter, M., Völkl, H., Waldegger, S., Gulbins, E., et al. (1998). Functional significance of cell volume regulatory mechanisms. Physiological Reviews, 78(1), 247-306.

Lieberman, H. R. (2007). Hydration and cognition: a critical review and recommendations for future research. Journal of the American College of Nutrition, 26(5 Suppl), 555S-561S.

Maughan, R. J., Shirreffs, S. M., & Watson, P. (2007). Exercise, heat, hydration and the brain. Journal of the American College of Nutrition, 26(5 Suppl), 604S-612S.

Murray, R. (1998). Rehydration strategies–balancing substrate, fluid, and electrolyte provision. International Journal of Sports Medicine, 19 Suppl 2, S133-5.

Suhr, J. A., Hall, J., Patterson, S. M., & Niinistö, R. T. (2004). The relation of hydration status to cognitive performance in healthy older adults. International Journal of Psychophysiology: Official Journal of the International Organization of Psychophysiology, 53(2), 121-5.

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