Does coffee dehydrate the body?
No — a long-debunked myth. Coffee has a slightly diuretic effect, but the fluid balances out. The DGE confirms: coffee counts towards your daily fluid intake.
Does coffee dehydrate the body?
No — a long-debunked myth. Coffee has a slightly diuretic effect, but the fluid balances out. The DGE confirms: coffee counts towards your daily fluid intake.
Why that is the case
The myth persists: “For every cup of coffee, drink a glass of water because coffee draws water from the body.” This simply isn’t true — and science has repeatedly proven it wrong.
What actually happens:
Caffeine has a mild diuretic effect — it stimulates the kidneys to produce slightly more urine. However, this effect is minimal and is more than offset by the amount of liquid in the coffee itself. A cup of coffee contains around 200 ml of water. The diuretic effect “costs” perhaps 20–30 ml of that — leaving a net fluid gain.
What the research says:
- A widely cited study by the University of Birmingham (2014) compared water and coffee as fluid sources: no significant difference in hydration levels.
- The German Nutrition Society (DGE) officially counts coffee towards the daily fluid balance.
- The diuretic effect decreases further with regular consumption due to habituation.
Where does the myth come from?
Probably from a study dating back to the 1920s, which observed increased urine production following high single doses of caffeine (isolated, not as coffee). This was uncritically applied to normal coffee consumption and has become ingrained in general knowledge.
The glass of water with your coffee is still a good idea though — not because of dehydration, but because it neutralizes your palate, allowing you to taste the coffee aromas better.
In practice at Green Wall Coffee
At Sophienstraße 27, we serve a glass of water with every espresso — not as a medical necessity, but as a ritual of enjoyment. A sip of water before your first sip of coffee cleanses the palate and makes the flavors more intense.
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