For better brain function, just add water

The body is mainly water, and I believe maintaining hydration is an important component of optimal health. I wrote most recently about this back in February (see here). This blog piece details some of the major roles that water has in the body (e.g. as a temperature regulator, carrier and building material). In practice, I have noticed that dehydration has the capacity to provoke many adverse symptoms, perhaps the most common of which is lethargy – particularly mental lethargy. It’s based on clinical observation, but I generally believe that maintaining hydration is important for fluid thinking.

I was therefore interested to read a recent study in which the affects of dehydration on brain function was tested [1]. The study essentially induced dehydration in individuals by having them exercise in a warm environment. Their brain function was assessed using what is known as functional magnetic resonance imaging. Part of this test involved subjecting individuals to an assessment known as the blood-oxygen-level-dependent (BOLD) response, which essentially measures the increase in resources (oxygen and nutrients) diverted to a part of the brain once activated.

The subjects, after being made dehydrated, were assessed with a problem solving test. Compared to a better hydrated state, those who were dehydrated has a great BOLD response. What this essentially suggests is that a dehydrated brain requires more resources (has to work harder) to get the same result. The authors of this study concluded that “Given the limited availability of brain metabolic resources, these findings suggest that prolonged states of reduced water intake may adversely impact executive functions such as planning and visuo-spatial processing.”

Here, it seems we have at least some subjective evidence which suggests that hydration is important for optimal brain function. I advise individuals to drink enough water to keep their urine pale yellow in colour right throughout the day. Should urine stray into darker tones, I suggest upping water intake. I have found in practice, that just this one simple measure usually increases energy levels (including mental energy) within half an hour or so.

This study was actually performed in adolescents. As I was reminded yesterday by a friend, exam time is looming for many adolescents. One simple thing that may help their revision and exam performance is for them to simply add water.


1. Kempton KJ, et al. Dehydration affects brain structure and function in healthy adolescents. Human Brain Mapping 24 March 2010 [epub ahead of print]

12 Responses to For better brain function, just add water

  1. Jill Bishop 21 May 2010 at 3:43 pm #

    Dear John,

    I was interested to read your comments on hydration, but have you tried a water ioniser? We have been using one for seven weeks now and the major change has been in my husband’s blood sugar levels. He has been trying to reduce these since November 2008 and takes a weekly reading to see how he is getting on. He has severely reduced his intake of carbohydrates since that date and having followed your blog on the subject of Vitamin D in January 2010, we both began on 5,000iu of Vitamin D3. The diet helped, but it is the water ioniser which has brought his blood sugar readings down to an acceptable level. The readings are as follows:

    November 2008: 160
    November 2009: 135
    30 March 2010: 131
    Water ioniser installed: 1st April 2010
    6 and 13 April: 127
    20 April: 106
    27 April: 97
    11 May: 92

    His level has since risen to 107 as he has added a few more carbohydrates to his diet, but that is still within the recommended levels.

    I would be interested to know if you or anyone else has any experience with a water ioniser. My sense of smell has certainly improved.

    Best wishes,


  2. Haider 21 May 2010 at 4:58 pm #

    Drinking fluids or just plain water when dehydrated indeed does give a feeling of well being and better understanding. But how much and at what intervals, with meals or after meals need be explained.
    Also about hot water/ cold water controversy?

  3. michael 21 May 2010 at 8:05 pm #

    Re Barbara’s comment I guess it’s all down to the quality, choice and volume. Provide anyone with a nutritionally balanced balanced diet in moderate quantities (with enough fluids, of course) and they will undoubtedly benefit, especially as the years roll by.

  4. Baarbara 21 May 2010 at 8:22 pm #

    Something different (NOT CONNECTED TO THE Water topic):

    I have just seen the film about and read up on the American Cook and writer Julia Child, who popularised French cordon bleu cooking.
    What strikes me is that this woman, as well as her husband who ate her food every day, both lived to the ripe old age of 92! This after eating ‘rich’ food (albeit using butter, not cooking oils) for decades (she started on French cuisine in her mid-thirties), and it seems also without doing much exercise (which wasn’t a ‘must do’ in those days yet)!
    Could it be that it was their ‘joie de vivre’ that kept them up and running?
    I also know of other people who became over 80 or 90 without cutting down on fats or eating a lot of salads and veggies, and who also did not exercise in the modern sense.

    What is your take on this?

  5. john Sampson 22 May 2010 at 4:23 pm #

    “Your Body’s Many Cries for Water” by Dr F Batmanghelidj has a lot of interesting information regarding this topic.

  6. Paul 23 May 2010 at 9:01 am #

    @Jill – It’s not clear from your post if it’s the water ionizer that is helping, or if your husband is (a) simply drinking more fluid than before, or (b) drinking water as a substitute for a caffeinated drink that could have been affecting his blood sugar (e.g. do a google on ‘caffeine blood sugar’). Do you have any further comment?

    @John – I cannot find the Kempton paper online but I am know that if I exercised in a warm environment, I would also feel over-heated. If the hydrating subjects were also drinking cold water, maybe they were keeping their core temperature down? (as well as hydrating).
    Is it clear from the paper that the effect is due to hydration?

  7. Xenia 24 May 2010 at 3:32 pm #


    my take – and also my experience – is that, apart from joie de vivre, what keeps the body and mind sane, healthy, vital and young is REAL food. Julia’s cooking was from the scratch – it makes a big difference if you know what goes into your food and if you use healthy fats and other natural ingredients, instead of buying prepackaged stuff and all the non-foods out there. An example: if you make mayonnaise at home, you only need some healthy oil (I use virgin olive oil), free range eggs, salt, pepper and some lemon juice. I also like to add lots of turmeric and cayenne pepper. If however the mayonnaise is store bought, it is not food anymore. It contains a long list of unrecignizable ingredients, including sugar, fillers, thickeners, modifiers, preservatives, colorants – you name it. If you cook your own food you also tend to eat more low-carb, I think. You don’t buy energy bars, energy drinks, artificial “food products” that not only contain lots of chemicals but are usually also full of sugar, HFCS, MSG, aspartame, soy, gluten etc. All of which make your life shorter and more miserable.

    So it is not just about low-carb (which for me is the basis of everything), it is also about the integrity of food. Do not put anything in your mouth that is not food. If it is man-made, it is not food. It also depends a lot on how it was raised/grown. If it comes with pesticides, vaccines, antibiotics, fertilizer residues … ot GMOs, it is NOT food. If it is fortified, it is NOT food. For me, food is also pretty much only what could be eaten raw (even if we do cook it now). We cook meat and fish but we can also eat carpaccio or sushi which is raw. But potatoes, corn, wheat, beans, soy etc. can not be eaten raw. I find this a pretty good rule for health and longevity. Fermented foods are helpful as well.

    There’s a great book I warmly recommend – Real Food by Nina Planck. Also all the books by Marion Nestle.

  8. Xenia 24 May 2010 at 3:43 pm #

    And yes, they make it quite difficult for you to find real food today. It is almost a detective’s job to successfully avoid all of their garbage … It took me several years to find all of my real food sources. But it sure was worth its while.

    I think today each person should plan to grow at least some of their own food in future. Because uncompromised food will be increasingly more expensive and scarce and difficult to find …

  9. Jill Bishop 28 May 2010 at 12:08 am #

    An answer for Paul.

    Thank you for your comments, but my husband hasn’t changed his habits at all! He has a mug of tea twice a day and coffee about once a week at home (ie made with ionised water). He also has a Costa coffee about twice a week. As before he drinks three or four large glasses of water a day on top of this and wine in the evening. His last few blood sugar level readings have remained below 110.

    I cannot think of anything else which has changed apart from the ionised water and we have tried an awful lot of things since November 2008. As you suggested, I have read some of the Internet information on the relation between caffeine and blood sugar, but my husband checks his blood sugar in the early morning before eating to be consistent.

    We will be on holiday for three weeks in September, so it will be interesting to see if his blood sugar creeps up again. However he just may have given up testing it by then!

  10. Paul 29 May 2010 at 11:44 pm #

    To Jill.
    Thanks for the further information. That’s an interesting as well as very positive experience!

  11. holger 12 January 2011 at 8:28 pm #

    thanks for info i had a project to do but could u find out how much percentige of water our body is made up of please. thanks!

  12. Ryan Critchett 6 January 2012 at 4:17 am #

    It’s all true. I’m a real brain conscious guy. Whenever there’s a deficit, I know it and try to fill the gap immediately. Sometimes it’s water (particularly after long jogs), and drinking more and re-hydrating, even just a little bit (doesn’t have to be anything crazy) almost immediately improves cognitive function. It’s soooooo a big deal.

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