When I’m sweating like a pig and panting like a dog in spin class, the last thing I want to sip on is a hot cup of Java.
That might be why the common “coffee dehydrates you” belief is so easy to subscribe to ― there’s something about the slightly bitter beverage that feels drying, rather than hydrating, isn’t there?
After all, coffee is a known diuretic (like a laxative, but for pee), especially in high doses.
If the drink makes you lose water and is less thirst-quenching than regular H2O, it makes sense that you’d become more dehydrated the more you drink, right?
Possibly, slightly ― but only at very high levels
Though coffee does make us visit the loo more often, experts think that’s more than covered by the fact that, well, coffee is made with lots of water.
One 2014 paper found that “moderate” coffee drinking (in this case, 800ml a day drunk by adult men) is about as hydrating as water.
Another 2014 review of studies suggested that while drinking roughly three cups (710ml) of coffee increased how much participants peed by 109 ml compared with their urine output after drinking the same amount of caffeine-free liquid, it was still a net hydrator by a considerable margin.
The NHS says that when considering your daily fluid intake, “Water, lower-fat milk and sugar-free drinks, including tea and coffee, all count”.
So, while water is still your best bet overall, you don’t need to panic about dehydration if you love your morning coffee.
Can you drink too much coffee?
The Mayo Clinic writes that we should stay under 400mg of caffeine a day, adding: “Very high doses of caffeine, greater than 10 milligrams per kilogram daily, are linked to serious health conditions.”
At those very elevated doses, caffeine is associated with heart issues and even stroke. Even before that, going over the suggested limit can cause an upset stomach and may make some people anxious.