Q - I’ve heard that drinking tea and coffee is bad for you as they promote dehydration and so should be avoided by athletes as they harm performance. Is this true?
A - I commonly hear this question asked and the usual reply, by a well meaning person, is that tea and coffee are diuretics (lead to body water loss), contain ‘toxins’ or that you have to drink equivalent volume of water to counteract their water-losing effects. If this were true, Great Britain would be holding fewer medals at World and Olympic level! Sometimes dietary advice persists in nutrition based on anectdotal evidence, voodoo science and myth. Conclusions are drawn on topics that seem ‘obvious’ or logical and yet have not been subjected to the rigor of scientific appraisal. Professor Ron Maughan and accredited sports dietitian, Jane Griffin, recently reviewed the scientific evidence to look at the commonly held view that tea is a diuretic and that that normal tea drinking habits are associated with poor fluid balance.
The bottom line is that there is no evidence base in the scientific and medical
literature for the commonly quoted idea that all caffeine-containing drinks
should be avoided in situations where fluid balance is, or might become a
problem.
The broad conclusions from the literature review of the effect of caffeine
on fluid balance were:
| -
Large doses of caffeine have a diuretic action.The review cited a dose
of more than 300mg of caffeine e.g. 5-8 cups of tea (see
table for details) - Single doses at the levels found in commonly consumed beverages have little or no diuretic action - Regular caffeine users become habituated to the effects of caffeine, diminishing its action |
In the one study that looked at the effects of including caffeine-containing drinks in the diet of individuals following their normal daily activities, there was no effect on hydration status (Grandjean et al, 2000).
So drinking tea and coffee is not bad for you when it comes to hydration status.
Sports people would be advised to enjoy a variety of drinks: water, juices,
sports drinks as well as tea and coffee. So, if you enjoy your cuppa or have
a passion for a mocha, then continue. In addition to providing fluid, tea
(coffee and cocoa) are very important sources of the flavonoid group of antioxidants
that can add to the contribution made by fruit and vegetables to the overall
intake. Antioxidants are likely to provide beneficial effects against exercise-induced
tissue damage, so rather than being ‘toxic’, tea for example will
have beneficial effects. If you add milk to the drink, additional vitamins
and minerals will be provided. Health professionals and sports scientists
interested in nutrition can request a copy of the review by contacting Jennifer.poulter@virgin.net
tel: 01622 743266.
This advice should not replace that of your doctor or usual state registered dietitian. You should always discuss medical matters with your GP.