There’s a common sentiment that goes around currently in which people believe that the average human being requires at least 8 glasses of water in order to remain adequately hydrated. But is this true or is this just a myth? We will delve into scientific research as well as some scientific literature to check the veracity of this theory.
But first, where did this common hypothesis come from?
In 1974, two nutrition specialists, Dr. Frederick J. Stare and Dr. Margaret McWilliams authored a book: – Nutrition for Good Health in which they listed the recommended nutrition habits for longer more fulfilling lives. One question they answer is how much water a person should consume each day. The authors argued that one’s body has various physiological process that regulate this; but for the average adult, around 6 to 8 glasses for every 24 hours would suffice. They further added that this water can be obtained from tea, soft drinks, coffee, milk, beer, fruits and even vegetables. However, this recommendation became exaggerated over the years as most people believe that the 8 glasses suggestion is only exclusive to water.
However, is there any scientific literature to back this theory?
There is no single scientific paper that gives an explicit suggestion based on any scientific literature and this mainly attributed to the fact that individual water requirements will vary greatly from one individual due to factors such as body size and one’s level of physical activity as well as other variables such as the time of the year and one’s geographical location. Individuals with relatively larger body sizes will require more water; individuals who are very physically active require more water than their counterparts as they burn up water much faster. The time of year is important as well due to the changing seasons; you would need more during the hotter summer periods when your body uses up more water to maintain its necessary physiological process. In certain geographical areas such as sub-Saharan Africa the climate is generally warmer so inhabitants would require more water.
The Institute of Medicine did a panel on dietary reference intakes for electrolytes and water and concluded that there is no single daily total water requirement for a given person. Most academic papers conclude that for the average healthy individual, thirst can be used a simple guide to meet their daily water requirement. There are some exceptions to this such as the elderly or young infants where their thirst feedback may be unregulated.
Another popular belief is that caffeine does not count towards one’s daily hydration since it is believed that coffee is a mild diuretic (it promotes diuresis – the production of urine and thus lowers hydration levels in the body). However, an academic paper (Hydration Needs throughout the lifespan) in 2007 by Sheila Campbell concluded that, contrary to popular belief, tea, coffee and other caffeinated beverages do not increase urine output or negatively affect indicators of hydration status in individuals accustomed to consuming caffeine. Another surprising find would be that alcohol would increase diuresis in the initial 3 hours after consumption but would have an anti – diuretic effect 6 to 12 hours after alcohol consumption.
Using thirst as a guide would be suitable for regular activities but would not be the case for individuals who carry out strenuous activities or exercise. Academic papers have found a linked between dehydration and poor performance in the gym showing that dehydration could lead to a significant drop in muscular strength, power and even high – intensity endurance. The complication here is that thirst has a delayed onset meaning one is already about 2% dehydrated when they start to feel thirsty.
The practical recommendations for athletes would be to consume at least 6 ounces of water/fluid 20 minutes prior to the activity and another 7 ounces of water/fluid during exercise. In terms of daily intake, a recommendation by Lyle McDonald gives a practical recommendation based on one’s urine. One’s urine should be clear or slightly yellow throughout the day. The frequency of urinating is important as the average exercising adult should urinate 5 times a day and twice after a workout.
Finally, there is also the notion that water, cold water especially, can aid in fat loss by boosting metabolism is not grounded in any scientific literature. One 2015 academic paper by N Charriere et al showed that the vast majority of studies found little or no increase in resting energy expenditure (i.e. little or no metabolism) from water consumption. For those looking for a practical means to do this, a supplement such as Optiburn by Platinum Labs may be more useful for your goals.
All in all, this implies that the 8 glasses a day is a myth that is not grounded in any scientific literature and individuals should find the sweet spot at which they are adequately hydrated.