8 Things that Will Dehydrate You Fast

Drinking a lot of coffee

Well, according to experts, caffeine won’t dehydrate you, if you drink a reasonable amount, but things are different when you exercise. “In reasonable amounts, for people not overly sensitive, caffeine may be a useful performance-enhancing supplement,” says Andrews.

Nevertheless, people who consume more than 4 to 5 mg of caffeine per kilogram of body weight (2.2 pounds) can get dehydrated. 

“Drinking caffeine-containing beverages as part of a normal lifestyle doesn’t cause fluid loss in excess of the volume ingested. While caffeinated drinks may have a mild diuretic effect — meaning that they may cause the need to urinate — they don’t appear to increase the risk of dehydration. Water is probably your best bet to stay hydrated. It’s calorie-free, caffeine-free, inexpensive and readily available,” said Katherine Zeratsky, R.D., L.D. to Mayo Clinic.