A common belief in health and fitness circles is that it is somehow good for the body to drink an excessive amount of water.
A high water intake is claimed to lead to all sorts of health benefits, such as increased fat burning, more energy, less appetite, etc.
Here, I am going to discover what the actual science has to say about this.
Is there any real benefit to drinking more water than plain old thirst commands?
Or are we just wasting our effort filling and refilling those water bottles all the time? (not to mention having to pee every hour of the day)
First of All, How Much is Too Much?
Before I continue, I should clarify what “a lot of water” means.
“A lot of water” implies drinking many glasses of water per day, despite not being thirsty. People who do this often carry water bottles with them everywhere they go, and go to the bathroom to pee all the time.
There is such a thing as “too much water”, which is water intake to the extent that it becomes dangerous.
If you drink an insane amount, like in a water drinking contest (very stupid), you may go into a condition known as water intoxication, which can be deadly.
The body’s cells need a constant balance of various electrolytes (salts). When you pee and sweat, some electrolytes tend to get out along with the water.
Athletes that drink a lot of water to replace intense sweating, without replenishing the body’s salts, may dilute their body fluids. This can mess up the electrolyte balance and cause a condition known as hyponatremia, which can also be deadly.
Therefore, it is important to get in some electrolytes (salts) along with your water if you exercise intensely and sweat a lot. Some sports drinks include the necessary electrolytes to replace what is lost through sweat.
But given that you are not participating in a water drinking contest (you’re smarter than that, anyway), and that you make sure to replace massive sweating with both water and electrolytes, then drinking a lot of water is completely safe.
Water and Cognitive Function
Drinking a lot of water isn’t going to make you smarter, but there is a tiny bit of evidence to show that a mild dehydration can slightly impair mental function.
25 healthy women were dehydrated by means of either exercise or diuretics. On average, they lost a little over 1% of their body mass.
The women who were dehydrated had an increased perception of task difficulty, less focus, more symptoms of headache, and a degraded mood compared to controls (1).
Thus, it does seem like a good idea to make sure you do not get dehydrated, and take note that 1% of body mass is a very mild dehydration.
If you do feel a little blue at times, then perhaps you’re only a few glasses of water away from feeling your best again.
Water Intake and Bladder Cancer
There was one large-scale prospective study performed on 47.909 health professionals.
This study found water intake to be inversely associated with cancer of the urinary bladder, with those who drank 6 or more (1440ml+) cups per day half as likely to get bladder cancer than those drinking less than 1 cup per day (-240ml).
In fact, the authors noted that each additional cup (240ml) lowered the risk by 7% (2).
Water and Colorectal Cancer
Several studies show a significant protective effect of water intake against colorectal cancer, which is both common and deadly. In fact it is the third most common cause of cancer death.
Fluid Intake and Urinary Health
There is some evidence that drinking plenty of water might reduce chances of recurrence in patients who have been previously diagnosed and treated with kidney stones (8).
Water and its Effects on Satiety and Food Intake
A study of 20 young men discovered that those who consumed the greatest volume (600mL) of milk 30 minutes before a meal ate less than those who had a smaller volume (300mL).
Both volumes of milk had the same total energy content. The higher volume group was less hungry and also ate less at dinner 4 hours later (9)
Another study in 24 lean women found out that those who ate liquid food (soup) ate a lot less than those who had the same amount of food in solid form. However, eating the solid food with a glass of water on the side had no effect. (10)
An observational study of 5.783 chinese adults found that water intake was inversely associated with energy density of the diet, total energy intake and overweight status (11).
I’d like to point out, that despite water with a meal slightly increasing satiety, there is no indication that this would lead to weight loss in the long term, as there are so many other factors at play.
There is, however, a small chance that if you stay well hydrated throughout the day, you won’t feel as hungry and won’t eat as much.
If you really want to dig into the whole science behind water intake and health, then I recommend you take a look at this paper (12 – PDF).
Our bodies are 60% water and it is constantly being lost from the body, every minute of every day, through sweat, breath, urine and stool. The body doesn’t have any actual “stores” for water, like it has for body fat, and therefore it needs to be replaced all the time.
In fact, if you don’t drink water for a few days, you will die.
If you’re thirsty, water is the way to go. It is clean, calorie free, contains no additives and it’s really the only thing adult humans and pre-humans have been drinking for the last millions of years.
Elderly people may need to consciously make sure to drink water throughout the day as their brain may start to underestimate their required intake.
That being said, I do not see any reason why it would be a good idea for young, healthy people to drink a lot more water than what thirst commands. The mechanism in our brain that controls water balance is incredibly efficient.
A common recommendation is eight 8 ounce glasses of water per day (the 8×8 rule). According to the studies above, 5 glasses might be enough.
All in all, there doesn’t seem to be any reason to carry a water bottle around all day and drink so much that you have to pee all the time.
Make sure you don’t get dehydrated, drink a little bit of water throughout the day (especially with meals), but definitely increase your intake before, during and after workouts.
If you’ve got all that covered, then you have nothing to worry about.