According to the Mayo Clinic experts, consuming large quantities of caffeine does dehydrate you – but not in small quantities.
In years past, people thought that caffeine worked as a diuretic, an when consumed, would cause you to urinate more often. While this is true, you will not urinate excessively and cause your body to become dehydrated unless you drink large amounts of caffeinated drinks. A pot of coffee will cause you to become dehydrated, but a glass of diet soda or single cup of coffee will not.
Large quantities of caffeine equate to five or more cups of coffee a day, not one or two. Also, drinking excess caffeinated drinks may lead to feelings of nervousness, sleeplessness and even anxiety. In order to stay hydrated it is important to drink ample amounts of water regularly throughout the day.
There are caffeine free alternatives that can help you cut the caffeine in an effort to keep yourself hydrated. If you feel that you are becoming dehydrated, the best thing to do is drink water. This may seem obvious, but nearly 50% of all people who consume four or more cups of coffee each day also neglect their water intake and become medically dehydrated.
A good rule of thumb is to drink eight ounces of water for every cup of coffee or caffeinated tea you consume. This will keep you hydrated.