A New Year’s resolution idea: just add water

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I sat down two days ago with some ambition to write a blog post (or two). In the end I did not write a word. Why? As I explained to my girlfriend, ‘my brain wasn’t working’. Try as I might, I found the whole idea of writing anything cogent too much. I did a quick scan of things that might have caused this state. I was not short on sleep. Neither had I eaten any wheat (I’ve found from experience this tends to turn my brain off).

Then I wondered if I might be dehydrated. It was about 4.00 in the afternoon, and I could only remember passing water twice all day – not a good sign. Plus, there was no doubt in my mind that I had drunk only a small proportion of the water I would normally consume when, say, in my own home. I stepped up my water intake and felt quite quickly revived. It might have been a placebo response, but maybe not.

This morning I decided to see if there was any recent evidence on the impact of dehydration on mental functioning, and did indeed come across a relevant study [1]. In this research, 25 women were subjected to a variety of assessments of mood, mental functioning and wellbeing in a normally hydrated state, as well as a dehydrated state. On one occasion, dehydration was induced with intermittent exercise but not heat. On another occasion, dehydration was induced not just with exercise, but by administration of the diuretic drug frusemide (furosemide).

Overall, dehydration with or without frusemide led to an average of 1.36 per cent of body mass. Just to put this into perspective, for someone weighing 70 kg, this would equate to about 1 kg (or 1 litre) of dehydration. In other words, this extent of dehydration would be described as ‘mild’.

At this level of dehydration, basic cognitive (brain) function was not significantly affected. But other functions were, including the amount of perceived effort used by women to complete a task. My experience yesterday meant that I could totally relate to this.

In addition, the concentration and mood of the women were also adversely affected. The women were more fatigued too, and were more prone to headaches. All this, remember, was the result of relatively mild dehydration.

None of this actually proves my inertia yesterday was caused by something as simple and rectifiable as dehydration, but it is at least consistent with it. I’d say as far a New Year resolutions go, many of us could do a lot worse than just to ensure we’re decently hydrated. How much should we drink? I suggest enough to ensure our urine stays pale yellow in colour throughout the day.


1. Armstrong LE, et al. Mild Dehydration Affects Mood in Healthy Young Women J Nutr January 1, 2012 jn.111.142000

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