RCTHumann = 262011
Mild dehydration impairs cognitive performance and mood of men.
Plain-language summary
This study set out to see how mild dehydration affects thinking and mood in young men. It compared three conditions: dehydration from exercise plus a diuretic, dehydration from exercise alone, and staying hydrated while exercising. Men walked on a treadmill in a warm room, and their thinking skills and mood were tested. The study found that mild dehydration, even without overheating, made men less alert, slowed their memory, and left them more tired and tense.
Key findings
- Mild dehydration increased errors on visual vigilance tasks.
- Dehydration slowed response times on visual working memory tasks.
- Dehydration raised feelings of fatigue and tension/anxiety at rest.
- Dehydration also increased fatigue during exercise.
- Plasma osmolality (a measure of hydration) rose with dehydration.
How to analyze the study yourself
- Study type
- In this crossover every man completed all three conditions and was compared against himself, so differences between people cannot explain the result. With 26 men it shows the direction of the change rather than how large it is across the population.
- Population
- The study included young men with a mean age of 20.0 years.
- Funding
- Not reported
- Takeaway
- This study found that losing about 1.6% of body weight in fluid was enough to make young men slower on memory tasks and more error-prone on attention tasks, and to leave them more tired and more tense, with their core temperature unchanged. Part of that loss came from a diuretic rather than from sweat alone, and it is small enough that you would not necessarily notice it as thirst. If you are working or training somewhere warm, drink before you feel you need to, because the thinking cost arrives before the discomfort does.