Is Coffee Dehydrating?

You’ve probably heard that caffeine is extremely dehydrating – that used to be the conventional wisdom, and it’s what I was taught, too. But in this case, common knowledge was incorrect. The record has now been set straight, thanks to Lawrence Armstrong, a researcher and professor of exercise physiology. In a comprehensive review article published in The International Journal of Sports Nutrition and Exercise Metabolism, Armstrong concluded that caffeinated beverages create only a mild diuretic effect. What’s more, if you drink coffee daily (I’m talking to you, my fellow java junkies!), your body quickly builds up a tolerance to this modest effect. If you’re a regular drinker, coffee hydrates similarly to water, so it actually counts towards your daily fluid goal.

But before you go out and buy a super-sized mug of joe, remember that Armstrong’s analysis was based on the consumption of moderate amounts of coffee – that is, one to four cups per day. In excessive amounts, regular coffee may have a more significant dehydrating effect, not to mention trigger jitteriness and disrupt sleep. And, of course, you still need to drink plenty of plain H2O throughout the day to keep your body happily hydrated.