You’ll often hear that caffeine should be avoided because it will dehydrate you. Despite this knowledge being around for many years, people (and a lot of healthcare professionals) still like to say this, even though its been long disproven.

Once we began to appreciate the importance of maintaining a good hydration state, it was at this time that caffeine, a diuretic (water-wasting) was declared public enemy number one to optimal hydration.  It was thought that caffeine-containing beverages would put athletes at a disadvantage, as it would dehydrate them, cause their body to lose electrolytes (the minerals that aid in a number of exercise-dependent physiological process such as muscle contraction) and put them at risk for hyperthermia (overheating).

A Fresh Look at Caffeine

Well, a big study actually took a look at this information. The study investigators reviewed the outcomes of numerous caffeine studies over the last 75 years and compiled all of the data for a comprehensive review. What they found was that moderate to high (240-642 mg of caffeine) caffeine consumption does not induce diuresis any more than plain water, or that it contributes to chronic dehydration, negative exercise performance or temperature dysregulation in a hot environment.

The researches did note that moderate caffeine consumption may possibly increase sodium loss very slightly, however they argue that our society’s more than adequate dietary sodium consumption compensates for this loss of sodium. In other words, there’s so much salt in our food that losing a bit from caffeine consumption won’t hurt.

The study also claims that while caffeine is a diuretic, the body will retain the water it would have lost from this effect from the fluid of the beverage. And, those that regularly consume caffeine will adapt to the diuretic effect and thereby lose even less water.  Lastly, the researchers conclude that very little is know about the effects of extremely large doses of caffeine (over 600 mg) on the above topics, and that more research is needed.

Caffeine: The Numbers

So, how much is too much? The average cup of coffee contains anywhere from 75 to 250 milligrams depending on how it’s brewed; 12 ounce sodas contain 30-50 milligrams; tea contains roughly 50 milligrams; energy drinks contain 80-100 milligrams; and 1 tablet of NoDoze contains 200 milligrams.

These are very general numbers; caffeine content can vary widely especially among beverages that are brewed (coffee and tea).

What's It Good For?

It used to be that caffeine was a double-edged sword.  Despite being known as a (legal) performance-enhancing agent, it was also frowned upon for the aforementioned effects.  Caffeine can increase physical endurance and delays fatigue during exercise. It does not however, affect short burst exertion, such as during lifting or sprinting.

From 1984 to 2000, caffeine was a monitored substance by the World Anti-Doping Agency; athletes could be disqualified from competition if their urine was found to contain more than 12 micrograms/ml, or about 8 espresso shots worth. !!! 

Caffeine works by stimulating the brain, the heart, muscles and the lungs. In the brain, caffeine improves vigilance and psychomotor performance – think intensity and concentration. In the heart, it works to increase the strength and the speed at which the heart contracts, and helps it to deal with stressful situations more efficiently. In the lungs, it dilates the bronchioles and stimulates breathing, improving airway function. Caffeine enhances the efficiency of the muscles, and delays muscle exhaustion. More specific to athletic performance, caffeine can decrease one’s perceived level of exertion, or how hard they think they are working. This effect enables the athlete to feel less tired, and therefore have a better performance.

And if those effects weren’t enough, caffeine also has a mild analgesic (pain relieving) effect. Cool!

Take Home Message

Moderate caffeine consumption will not dehydrate you. In fact, a bit of caffeine might serve you well, performance-wise. However, this information shouldn’t be construed as a recommendation to start consuming caffeine. If you don’t already use caffeine, don’t start - keep in mind that the overwhelming majority of caffeine-containing beverages are unhealthy (soda, energy drinks, latte-frappe-chino specialty coffee drinks) to start with. Caffeine will not make one a better athlete; it only improves those aforementioned systems that are well trained and cared for.  There is no substance that a person can consume that will make up for good old-fashioned dedicated training, healthy diet, and recovery.

Large amounts of caffeine can be detrimental. It will raise blood pressure during times of psychological stress, and it can cause elevated heart rate and arrhythmias in certain individuals.

And even though this study says that caffeine will not dehydrate you, its always a good idea to use some common sense and make sure you still drink enough plain water each day if you consume caffeinated beverages.