Nutrition Myth #6 - Water = Good, Caffeine = Bad

Water is good for you  caffeine is bad.  Right?

Maybe.

While we are told to drink 6-8 glasses of water a day, there is surprisingly little evidence to this idea. (1-3)

Another common belief is that if you drink extra water the body will somehow store it.  But that depends on how fast you drink it; drink several glasses within a fifteen-minute period and you will just pass extra urine but if you spend more than two hours sipping the same amount, more liquid is retained. (4)

What is true is that water is good for you, it is one of the most important nutrients for our body and while not drinking enough is bad for you, just like food, consuming more is not necessarily ‘good’ for you.

But what about caffeine?   That should be avoided because it will ‘dehydrate’ you?

Very large doses of caffeine are known to increase the blood flow to the kidneys and to inhibit the absorption of sodium, which explains why it could act as a diuretic, dealing with the sodium which hasn’t been absorbed. But the exact mechanism is still a matter of debate.

A review of 10 studies (5) concluded that caffeine is a mild diuretic at most, with 12 out of 15 comparisons showing that people urinated the same amount, regardless of whether the water they drank contained added caffeine or not.

In a rare study (6) where people drank nothing but tea for the 12 hour duration of the trial, there was no difference in hydration levels between them and the people who drank the same quantity of boiled water.

Further controlled trials have shown no changes in levels of hydration when drinking black coffee compared to water. (7, 8)

In short, drinking caffeine-based beverages as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested.

How much caffeine is bad for you?

While there is often concern about the links between caffeine and heart health, a moderate amount of tea or coffee (400mg, equivalent to four or five cups a day) should be fine for most people.  Research shows that this level of caffeine intake shouldn’t be detrimental to your heart health, affect your cholesterol levels or heart rhythm; indeed, caffeine has benefits as a stimulant, increasing sports performance and memory amongst others.

Although drinking coffee has been shown to increase blood pressure, this effect is usually temporary and is minimised over time if you drink caffeinated drinks regularly.  Some people are more sensitive to caffeine and can experience palpitations.  If this is you, then it’s sensible to avoid caffeine. If not, chill out.

Energy drinks

Energy drinks have a bad reputation for their caffeine content, but in reality, they contain about the same as coffee - 80mg of caffeine per 250ml can of Red Bull and 150mg of caffeine per 500ml of Monster, and slightly more than black tea - 75mg per cup.

So drinking 5 Red Bull’s a day is still within normal limits.

However, the main reason to avoid energy drinks is that they can contain nearly seven teaspoons of sugar in one 250ml can – that’s the maximum amount we should be consuming in a whole day.  So if you enjoy energy drinks, choose sugar-free versions where possible.

Whilst aspartame is not great, it is nowhere near as bad for you as some media purport. The World Health Organisation recommends a maximum daily allowance of 40mg per kg of body weight per day. For a 90kg adult, that would be 3,600mg. A 355ml can of Diet Coke contains around 200mg of aspartame so you would need to drink 18 cans a day to hit that threshold.

References

  1. Valtin H.  (2002)  "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"?   American Journal of Physiology. Regulatory and Integrative and Comparative Physiology. Nov;283(5):R993-1004.

  2. Negoianu D, Goldfarb S.  (2008)  “Just add water”.  Journal of the American Society of Nephrology.  Jun; 19(6):1041-1043

  3. Wolf R, Wolf D, Rudikoff D, Parish LC.  (2010)  “Nutrition and water: drinking eight glasses of water a day ensures proper skin hydration-myth or reality?” Clinics in Dermatology.  Jul-Aug; 28(4):380-3.

  4. Shafiee MA, Charest AF, Cheema-Dhadli S, Glick DN, Napolova O, Roozbeh J, Semenova E, Sharman A, Halperin ML.  (2005)  “Defining conditions that lead to the retention of water: the importance of the arterial sodium concentration”.  Kidney International.  Feb; 67(2):613-21.

  5. Armstrong LE.  (2—2)  “Caffeine, body fluid-electrolyte balance, and exercise performance”. International Journal of Sport Nutrition and Exercise Metabolism.  Jun;12(2):189-206.

  6. Ruxton CH, Hart VA.  (2011)  “Black tea is not significantly different from water in the maintenance of normal hydration in human subjects: results from a randomised controlled trial”.  British Journal of Nutrition.  Aug;106(4):588-95.

  7. Grandjean AC, Reimers KJ, Bannick KE, Haven MC.  (2000)  “The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration”.  Journal of the American College of Nutrition.  Oct;19(5):591-600.

  8. Armstrong L,  Pumerantz A, Roti M, Judelson D, Watson G, Dias J, Sokmen B, Casa D, Maresh C, Lieberman H & Kellogg M.  (2005).  “Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption”.  International journal of sport nutrition and exercise metabolism. 15. 252-6