Catherine Crépeau – The Rumor Detector – Agence Science-Presse
A lot of health experts say that you should drink 1.5 litres of water a day, or 8 glasses, to replenish the water you eliminate daily. But where does this number come from? Is it correct? Does it hold even during a heat wave? The Rumor Detector looks into it.
The Origin of the Rumor
An average-sized person loses 2 to 2.5 litres a day of water through their urine, their poop, and their sweat. In theory, everyone should absorb that much water to avoid dehydration. Given that we take in about half a litre to a litre of water a day through our food, we should therefore drink 1.5 litres daily.
Except that this figure is an average, and doesn’t say everything.
The Facts
Water needs vary greatly from one person to another. It depends on your corpulence, your age, your physical activity, the temperature outside and the food you consume. A man weighing 80 kilos has to drink more than a 50 kilo man. Water consumption needs grow when you exercise, or when it’s hot outside.
Recommending that everyone should drink 8 glasses a day is inappropriate. Especially since we don’t know exactly where this figure comes from. It might be a misinterpretation of the U.S. Food and Nutrition Board published in 1945, where they included water ingested through food in their daily requirement.
In France, the recommendations of their national nutrition and health program take into account personal differences. They suggest that you drink 30 ml of water for each kilogram you weigh. That usually means 1 to 1.5 litres a day, added to what you get out of your food. They also add 0.5 litres for every degree the thermometer reaches over 38 °C.
The body adapts to the quantity of water it takes in. If you don’t drink enough, the kidneys will retain water; if you drink too much, the kidneys will raise the quantity of urine they produce and adjust the concentration of mineral salts (sodium, potassium, calcium) to maintain the body’s fluid balance.
In the cases of under-hydration or of hyper-hydration, the kidneys make their adjustments in less than 40 seconds. That explains why when we drink more than we’re thirsty for, we have to make a beeline for the toilet to pee; whereas if we don’t drink for hours, the body holds in its water.
The color of your urine will provide a clue. The darker your urine is, the less hydrated your body is. Urinating fairly clear pee every two hours is a sign that all is well.
Drinking Too Much…
Can we drink too much water? Yes, but you’d have to drink 10 litres a day to negatively affect your health. And the body has defense mechanisms it will deploy before you get to that stage.
In effect, when the body feels it is satiated it makes the swallowing reflex more difficult, according to a 2016 study; and it will provoke a constant need to urinate. On the other hand, abundant and frequent urination can lead to distention of the bladder, dilation of the ureter, hydronephrosis and kidney failure.
Other works indicate that drinking more water than you need is disagreeable and requires greater muscular effort than when you drink to quench your thirst.
The overconsumption of water can also provoke a drop in sodium in the blood, a rare condition called hyponatremia that can cause a rapid inflammation of the brain, convulsions, and death. Along with cardiac problems, it’s one of the main causes of death among young healthy persons at endurance activities like marathons. A lack of sodium can be caused by the overconsumption of water and heavy sweating.
… Or Not Enough?
On the other side of the coin, dehydration is linked to low energy levels, headaches, constipation and obesity. It can lead to problems like low blood pressure, cognitive issues or a loss of consciousness. Go beyond a drop in 10% of water and dehydration can be fatal.
You have to find a balance between drinking too much and not enough to maintain your bodily functions. Studies have shown that drinking sufficiently reduces the formation of kidney stones and lowers the number of bladder infections among sufferers.
Verdict
We don’t know where the advice to drink 8 glasses of water per day really comes from. Instead of sticking to a precise number, listen to the body’s signals. That way, you will drink the amount of water your body needs, and you will not feel thirsty. Another way of verifying if you’ve drunk enough s to keep track of how often you go to the bathroom to pee.
Leave a Reply