Hydration Reality Check: What Counts & How Much Is Necessary

We all know the golden rule when it comes to fluid intake:

Eight glasses of water daily (2L) for optimal health!

Well, according to a recent article in CBS News entitled ‘8 glasses of water a day an urban myth’, this well established rule could be yet another misinterpreted nutritional myth that has gained incredible social momentum. Personally, I’m always hesitant to accept news reports at face value due to their tendency to sensationalize claims. However, after some digging through various journals and electronic databases, the conclusion seemed to reinforce the basic gist of the article. For example, a recent article published in the Australian and New Zealand Journal of Public Health stated that while water was important for health, “the recommendation of 8 glasses of pure water per day appears an overestimation of requirements’ (Tsindos, 2012 pp. 206). They followed by suggesting that all fluids were important in meeting requirements, NOT JUST WATER. This is great news for coffee and tea drinkers as (although caffeine is a milk diuretic) human studies indicate that caffeine consumption of up to 500mg daily does not cause dehydration or chronic water imbalances. The published studies seem strongly suggest that, for SEDENTARY individuals, 8 glasses of water daily are not needed to maintain fluid balance and the proper regulation function of the osmoregulatory system.

Reading in Between the Lines:

OK, so we’ve established that tea, coffee and certain water-based foods such as lettuce contribute to the daily water intake and that such large quantities of water intake (8 glasses-rule) is not necessary for the average individual. However, there is always a YES, BUT in such situations. In this case the research does confirm that fluid intake equal to and surpassing 8 glasses daily are advisable for the treatment or prevention of certain diseases and under some special circumstances such as vigorous work and exercise, especially in hot climates.

Take Home Messages:

• Tea & Coffee contribute to daily fluid balance levels.
• Caffeine intake of up to 500mg per day does not appear to affect water balance.
• It is advisable for ndividuals engaged in vigorous exercise or those who need to manage / prevent certain medical conditions to either rech or exceed the 8-glasses rules.

References:

Tsindos, S. (2012). What drove us to drink 2 litres of water a day?Australian and New Zealand Journal of Public Health, 36(3), 205-207.

Valtin, H. (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for ‘8x8’?AJP - regu Physiol, 1(5), 993-1004.

Popkin, B. M., Armstrong, L. W., Bray, G. M., Caballero, B., Frei, B., & Willett, W.C. (2006). A new proposed guidance system for beverage consumption in the United States.American Journal of Clinical Nutrition, 83(3), 529-542.