No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population

Coffee is one of the most consumed beverages in the US, but is it partially to blame for our general trend toward dehydration? Some research suggests that the caffeine found in coffee might not be as healthy as we thought, as it reduces sodium reabsorption and can have a diuretic effect when consumed in amounts over 500mg. In this study, researchers analyzed the effects of consistent caffeine consumption on hydration levels to add some evidence to the debate.

This counterbalanced, cross-over study, included 50 participants who regularly drink 3-6 cups of coffee per day. In the first of two trials, participants were given 4 mugs of Nescafe original (not a sponsor) over the course of a day. Their diet was controlled, alcohol prohibited, and exercise forbidden with the intention of keeping all fluids in the body. Researchers analyzed pre- and post-caffeine urine, along with blood markers and total body water. The participants did the identical protocol again in the second trial except the coffee was replaced with water.

The results show that total body water stayed the same throughout the experiment, as did blood markers, bowel movements, and hydration status. In other words, the caffeine veterans drank a moderate amount of coffee and still remained hydrated.

Takeaway
Consistently drinking coffee appears to negate the diuretic effect of caffeine. We're all trying to get enough water in a day, and it's nice to see that up to four cups of coffee can add to hydration, not worsen it.