Four cups of coffee a day hydrated similarly to water
Fifty healthy men used to drinking coffee had each drink for three days: body water and urine were similar. Coffee produced more urinary sodium.
The key idea
Across three days of coffee or water, the main hydration indicators in men accustomed to coffee were similar.
The study, in plain language
The team compared coffee and water in 50 healthy men accustomed to drinking coffee. Each completed two three-day periods, separated by ten days: in one they drank four cups of coffee per day and in the other the same volume of water; the order was randomized. Diet and other fluids were controlled, and exercise was avoided.
There were no differences in total body water or urine volume and concentration. More sodium was excreted in urine with coffee, but other hydration indicators did not change. The comparison addressed a focused question using several measures, not just how often someone went to the bathroom. Limitations: three days per drink, only healthy men accustomed to coffee, and no evidence about other amounts, people, or settings.
What they found
- Total body water was similar after drinking coffee and after drinking water.
- Urine volume and concentration were also similar for the two drinks.
- More sodium was excreted in urine with coffee, while other hydration indicators showed no changes.
Something to think about
If someone tells you a drink changes urine, what other signals would you look at to know whether it dehydrates you? Here sodium changed, while the other indicators were similar.
How they studied it
Each of 50 healthy men accustomed to coffee tried both options in randomized order: three days of coffee and three of water, separated by ten days. Researchers measured body water, urine, and blood. The test lasted three days per drink and included only healthy men accustomed to coffee, so it does not resolve long-term effects or other groups.
What the study cannot show
- The comparison covered three measured days per drink and included only healthy men who regularly drank coffee. Exercise was avoided during the trial.
- Results apply to these amounts and conditions, not other populations, consumption levels, or circumstances such as intense heat.
The original study
No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population
Source under CC BY 4.0. English adaptation and explanation by PaperFlow, with AI assistance. The text has been reorganized for a general audience; it is not the complete paper and does not imply endorsement by its authors.
One study alone does not represent a field's consensus. Educational content does not replace professional advice. Report a possible error.
