Caffeine, coffee, tea & diuresis

I attended a lecture you gave about maximizing muscle recovery during high intensity training. I had a question about caffeine. How much caffeine can you drink per day in season, and are there particular times during the day it is okay to drink caffeine? I drink coffee daily, and often have it 30 minutes before morning practices start. Will this hurt my performance? Mandy

ANSWER: Caffeine has been correlated to diuresis (water loss) in the amount of 1.17 ml / mg caffeine [Stookey JD, Eur J Epidemiol 15 (1999) 181] but when consuming less than 1 cup of coffee (about 100 mg caffeine, although this number varies widely) the diuretic effect is generally not noticeable in most people. Studies show measurable diuresis for most people starts at around 1.5 cups of regular coffee, with nearly everyone seeing the effects at 3 cups of coffee. In other research, the diuretic effect was shown to occur with decaffeinated coffee as well, indicating that the diuretic effect is not due entirely to caffeine, but so far I have only seen one paper that addresses this particularly interesting question (we will see what comes out on this in the future). What we know for now is that caffeine is a mild diuretic, that it binds to adenosine receptors in the brain, increasing dopamine acitivity and increases adrenaline, beta endorphin and free fatty acid levels in the blood, all of which likely contribute to the mild endurance benefits observed from caffeine intake in athletes. Research has shown that the benefits occur only with low levels of intake and then plateau, either because the effects of caffeine become saturated in the body or because the diuretic effect starts to reduce performance so that the caffeine benefits are partly cancelled out. Caffeine is a "methylxanthine". Methylxanthines (caffeine but also othe related compounds) have been found in tea (which is therefore also a mild diuretic) and cocoa i.e. chocolate. The half-life in the body of methylxanthines is between 4-6 hours, so if you have a cup of coffee containing 100 mg of caffeine at 6 pm you are probably down to 50 mg of caffeine at 10 or 11 pm, which for some people is enough to reduce sleep quality. My recommendations: Have no more than 1-1.5 standard cups of coffee in any 2-3 hour time period (or the equivalent amount of expresso) to avoid diuresis and do not drink any coffee in the second half of your day. You could drink a bit more tea than this but I would not more than double this amount, and if you see increased urination from what you would expect from the equivalent amount of water, reduce your coffee or tea intake next time. In terms of athletic performance there should be no negatives with one cup as long as you are drinking water in addition to this.

Comments

[max cougar oswald ( Stanford '12 )]

The safe zone for hydration could be more than just 100mg. I just read this in the NY Times - this study in 2008 found that drinking up to 550 mg of caffeine will still evade the a diuretic effect.

"In March the Center for Science in the Public Interest published a comprehensive appraisal of scientific reports in its Nutrition Action Healthletter...

...Hydration: It was long thought that caffeinated beverages were diuretics, but studies reviewed last year found that people who consumed drinks with up to 550 milligrams of caffeine produced no more urine than when drinking fluids free of caffeine. Above 575 milligrams, the drug was a diuretic.

So even a Starbucks grande, with 330 milligrams of caffeine, will not send you to a bathroom any sooner than if you drank 16 ounces of pure water. Drinks containing usual doses of caffeine are hydrating and, like water, contribute to the body's daily water needs."