Member Case Study: Diuretic Effect from Tea, Coffee

author : AMSSM

comments : 1

Recent studies have demonstrated that moderate to mild levels of caffeine (less than 300mg) do not promote dehydration during exercise.

Member Question from KSB

I have always wondered what the net fluid/hydration gain is from drinking tea and coffee. I am not a good hydrator but I am a crazy (Brit) tea drinker. A recent UConn study said that there was no or little diuretic effect from tea but I have always wondered for example, if I drink 8 oz of water in a cup of tea (or coffee), is there any hydration net gain that might count towards fluid intake? Or is the diuretic effect equivalent to an 8oz fluid loss so it's a push?
 

Answer from Andrew Getzin, MD

Member AMSSM

We have become a society that loves our caffeinated beverages. In addition, many triathletes use caffeine as an ergogenic aid to help them go faster. Caffeine (and theophylline, which is found in tea in addition to caffeine) acts as a central nervous system stimulant that can potentially improve performance. However, maintaining appropriate hydration is important to help with heat dissipation and limit cramp formation during exercise.

Older studies have shown that ingestion of high quantities of caffeine (300mg, or more than 3-6 cups of coffee or tea) can increase urine output in people who are not exercising. Endurance athletes have extrapolated this information to mean that they should not consume caffeine while exercising due to an increase risk of dehydration. However, recent studies (including one by Armstrong et. Al., from the University of Connecticut) have demonstrated that moderate to mild levels of caffeine (less than 300mg) do not promote dehydration during exercise.

It is hypothesized that the hormones released during exercise limit renal blood flow and thereby limit the potential diuretic effect of caffeine. Although there still needs to be more research, drinking an eight-ounce cup of tea before or during exercise would overall improve your hydration status and not make you more dehydrated.

If you are unsure of how much to drink during a race, consider a practice session where you mimic race conditions and weigh yourself before and after your training session. Replenish fluids during the session as you would normally on the day of the race. Your weight should be about the same when you end as when you started.

I personally, as a triathlete and a sports medicine doctor, plan on continuing my morning cup of coffee on race day and ingesting caffeine during races that last longer than 2 hours.

Andrew Getzin, MD

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date: July 11, 2007