It doesn't make you thirsty after all.
Take a situation many of us have experienced first hand: You wake up, make yourself a cup of coffee at home, or head to office and brew one there, and almost immediately after finishing, you have to sprint to the bathroom. Most people assumed that because coffee is a diuretic—it won't keep you hydrated. We’re under that impression because of a popular study released in 1928 (which studied only three people), which incorrectly stated that coffee’s diuretic properties lead to dehydration, but has since been the authority on the subject. Why is it so wrong? Because excess urination doesn’t automatically mean that you’ll get dehydrated. The study had another flaw: It said that people who drank even half a cup of coffee after abstaining from coffee for two months saw a noticeable increase in trips to the bathroom, and did not study people who regularly consumed the beverage.
A new study from the American Journal of Clinical Nutrition is making up for its predecessor’s mistakes. This one created a “beverage hydration index” ranking how 13 different popular drinks effected the body's fluid retention by measuring both how often the study’s participants had to use the bathroom and the resulting "fluid balance", compared to water, in order to identify which drinks are the best for "short term hydration." Turns out that yes, you can stay hydrated by drinking coffee, even though it might make you have to pee. But researchers don’t recommend hydrating with coffee alone: It had the weakest hydrating effects of all the tested drinks, falling behind beer and even skim milk.
This study comes on the heels of another, which finally clears up the myths about how much coffee is too much. In fact, most people can drink up to four cups of regular brewed 8-ounce coffee every day without any ill effects. You can add this to your list of reasons why you should never feel guilty about enjoying your morning cup of joe.