Does Coffee Really Dehydrate You?

What’s the background?

Caffeine is known to have a diuretic effect when consumed in high doses. Since coffee contains caffeine, is therefore widely assumed that drinking coffee leads to dehydration. However, some studies have reported that regular consumption of caffeine leads to resistance to its diuretic effects, which may mean that a regular caffeine habit does not lead to a reduced hydration status.

What did the researchers do?

The researchers recruited 52 healthy and non-smoking males aged 18 – 46 years who were moderate coffee drinkers, as defined by the consumption of 3 – 6 cups per day (300- 600mg/day caffeine). Coffee consumption was assessed by a 3-day food diary.

What happened?

The researchers reported that there were no significant differences between the treatments in respect of: bodyweight changes, 24-hour urine volume, urine specific gravity, urine osmolality, urine creatinine, serum osmolality, hematocrit, total plasma protein, serum sodium, serum potassium did not differ between conditions did not differ significantly between the two treatment conditions. Thus, the findings demonstrated no significant effect of coffee across a wide range of hydration assessment indices in comparison with water.

What did the researchers conclude?

The researchers concluded that moderate coffee consumption (4mg of caffeine per kg of bodyweight over 4 mugs per day) did not result in dehydration. They suggest that advice should not be given to the effect that moderate coffee intake is dehydrating.

What are the practical implications?

Strength athletes who habitually consume caffeine pre-workout in the form of coffee only do not need to take care to drink additional water to compensate for the dehydrating effect of coffee.

Individuals who enjoy drinking coffee habitually in moderate amounts do not need to consume extra fluids to compensate for the dehydrating effect of coffee prior to engaging in exercise.

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