Coffee’s diuretic effects may be a “wee” bit misunderstood.
Coffee has long been considered a strange paradox: It’s the fluid that doesn’t hydrate you. Despite drinking more (and more and more), coffee allegedly throws off your fluid balance and can result in dehydration.
… Or at least, that’s what they say. New research suggests this may not be the case.
It’s true that coffee is a diuretic, which is a substance that causes the kidneys to pass more urine (and make you have to hit the bathroom more often). Diuretics are sometimes given as medication to treat high blood pressure and edema, but they are also in some of the things we eat and drink, like caffeine and alcohol.
When you urinate more after consuming diuretics, your body is getting rid of salt and water, according to the U.S. National Library of Medicine. This alters the body’s fluid balance and can affect your hydration levels—despite the fact that you’re drinking cup after cup of fluids.
But here’s the rub: Most people can develop a tolerance to caffeine’s effects—including the “jittery” effect on the central nervous system and the diuretic effect on the kidneys.
At first, drinking coffee may cause you to have to pee more. But among habitual coffee drinkers, dehydration doesn’t seem to be an issue. For example, one 2014 study found no difference in total body water or urine output among regular coffee drinkers when they were drinking coffee compared to drinking water.
Of course, moderation is still advised. Most people can safely consume up to 400 milligrams of caffeine daily before experiencing unpleasant health problems, according to the U.S. National Library of Medicine. Some of those problems include abnormal heart rhythm, dizziness, headaches, dependency, and—yep—dehydration. Here are more signs you’re drinking too much coffee.
An 8-ounce cup of coffee contains anywhere from 95 to 200 milligrams, depending on how it’s roasted, the species and type of bean, and how it’s brewed. For example, light roasts tend to have more caffeine than dark roasts.
So coffee *could* cause dehydration, but only if you drank a lot of it. For most people, you can safely enjoy your cuppa joe without fear of messing up your hydration.
For your healthiest coffee, check out these tips:
Caffeine. Washington, DC: MedlinePlus, U.S. National Library of Medicine. (Accessed on October 9, 2018 at https://medlineplus.gov/caffeine.html.)
Diuretic. Bethesda, MD: National Cancer Institute. (Accessed on October 9, 2018 at https://www.cancer.gov/publications/dictionaries/cancer-terms/def/diuretic.)
Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014;9(1):e84154.
Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet. 2003 Dec;16(6):411-20.