BE­HIND THE HEAD­LINES WITH DR TIM CROWE

Is it true that caf­feine de­hy­drates you?

Healthy Food Guide (Australia) - - CONTENTS -

Did you know that wa­ter makes up over 60 per cent of your weight? All that wa­ter serves an im­por­tant pur­pose. Wa­ter helps reg­u­late body tem­per­a­ture; it trans­ports nu­tri­ents and waste prod­ucts and al­lows many meta­bolic re­ac­tions to oc­cur. You can see why there’s a big fo­cus on stay­ing well hy­drated.

If your wa­ter in­take (from foods and bev­er­ages) matches wa­ter losses (mostly from urine) then you have reached the happy place of fluid bal­ance. A di­uretic is some­thing that can up­set this del­i­cate bal­ance by caus­ing more wa­ter to be lost. Caf­feine was long seen as a di­uretic, but more re­search has found its ef­fect on fluid bal­ance is — at best — mi­nor.

A ker­nel of truth

There’s some truth to claims that caf­feine acts as a di­uretic, but the key is the amount you have. Early re­search stud­ies did find that caf­feine causes wa­ter loss, but the amount of caf­feine re­quired is over 500 mil­ligrams. That’s equal to 5–6 cups of cof­fee, or an even greater num­ber of cups of tea.

In a re­cent study in­ves­ti­gat­ing how cof­fee can af­fect hy­dra­tion, 50 reg­u­lar cof­fee drinkers un­der­went a va­ri­ety of tests to mea­sure their hy­dra­tion over three days. The hy­dra­tion tests were

re­peated af­ter they swapped their cof­fee for wa­ter for three days. Their food, fluid and their ex­er­cise habits stayed con­stant.

The re­search team found that af­ter all that drink­ing and test­ing, the ef­fect of caf­feine or plain wa­ter on any mea­sure of hy­dra­tion was the same. The par­tic­i­pants were reg­u­lar cof­fee drinkers, so the re­sult may have been dif­fer­ent in peo­ple who con­sume lit­tle caf­feine. But if some­one drinks cof­fee rarely, then any ef­fect on hy­dra­tion will ul­ti­mately be fleet­ing.

Drinks all round?

With much in­ter­est in how dif­fer­ent drinks can af­fect fluid bal­ance, sci­en­tists have now de­vel­oped a ‘bev­er­age hy­dra­tion in­dex’. The in­dex ranks flu­ids by the bal­ance be­tween how much the body re­tains or loses fluid when com­pared against wa­ter over four hours. Us­ing this bev­er­age hy­dra­tion in­dex, there is lit­tle to sep­a­rate cof­fee and plain wa­ter. And the same also goes for cola, diet cola, tea, iced tea, or­ange juice and even sports drinks — they all can keep a per­son hy­drated just as well as wa­ter.

Mak­ing sense of it all

Be­fore your switch your drink­ing habits from ‘eight glasses of wa­ter’ to ‘eight cups of cof­fee’ a day to meet your fluid needs, a word of cau­tion. Drink­ing too much caf­feine is not good for your health. Poor sleep pat­terns and in­som­nia, ag­i­ta­tion, anx­i­ety and even heart pal­pi­ta­tions are well-de­scribed ef­fects of too much caf­feine. So keep­ing your daily caf­feine habit be­low roughly 400 mil­ligrams (about 4–5 cups of cof­fee) is the best goal.

For reg­u­lar drinkers of cof­fee and tea, the good news is that there is lit­tle need to worry about them de­hy­drat­ing you. An­other bit of good news is that cof­fee and tea have many health ben­e­fits linked to them in­clud­ing de­creased risk of some can­cers, heart dis­ease and even type 2 di­a­betes. So keep en­joy­ing your daily cuppa of choice!

Is caf­feine a di­uretic? It de­pends on how much you drink

Dr Tim Crowe is an Ad­vanced Ac­cred­ited Prac­tis­ing Di­eti­tian and nu­tri­tion re­search sci­en­tist. You can con­nect with him at think­ingnu­tri­tion.com.au To avoid in­som­nia & anx­i­ety, keep your daily caf­feine fix be­low 4–5 cups

Be­ing de­hy­drated can zap your en­ergy & make you feel tired

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