It’s been a controversial question: If you’re trying to stay properly hydrated, does coffee help you or hurt you? In a way, both answers make sense. Coffee, of course, is mostly water, so it stands to reason that it would. However, it does have a rather infamous side effect.
“Caffeine is a diuretic, in other words, it makes you pee,” said Dr. Seth Clohosey, an internal medicine physician with Trinity Health of New England, “and so the thought was, if you’re drinking something that makes you pee more, are we going to be losing more fluid than we’re taking in?”
The short answer is no - it doesn’t dehydrate you, so if you’re trying to eat and drink the (rough) equivalent of eight to twelve cups of water per day, caffeine is okay, so long as it’s consumed in moderation. The effect that caffeine has on the body, however, is a little more complicated.
“People have studied this actually pretty in detail to look at caffeine,” said Dr. Jeff Brown, from the CT Sports Medicine Institute at St. Francis, “it doesn’t cause dehydration as many people have thought, however you do urinate more and your body has to adapt to it to retain the fluid you have.”