What is the Right Amount of Water to Drink Every Day?

 It is commonly recommended to drink between 1.5 and 2 liters of water per day. However, these official recommendations might be incorrect or at least not suitable for everyone... Here is the very serious answer from scientists.

Water plays a central role in the human body. To give you an idea, an adult body weighing 70 kg is composed of 65% water. The amount of this element varies depending on body size and age. Ninety percent of this water is contained in the blood plasma. To stay healthy, it is necessary to maintain good hydration. A study published in the journal Sciencesuggests that the widely known recommendation of about 2 liters of water per day, or eight glasses a day, is not valid. But what is the right amount of water to consume daily to stay well hydrated?

The Role of Water

The human body is mainly composed of water. Proper hydration is essential to maintain its functioning and ensure essential functions such as:

  • Eliminating toxins and waste from the body
  • Regulating body temperature
  • Contributing to numerous chemical reactions
  • Aiding digestion
  • Transporting nutrients to cells
  • Managing the amount of blood and lymph

Signs of Good Hydration

Hydration is crucial, but it can be difficult to determine personal needs. One of the most direct indicators is the color of urine. Darker urine indicates severe dehydration, while lighter urine indicates very good hydration. Some additional signs to identify when thinking about hydration include:

  • Headaches, which are very common in the middle or end of the day, or after consuming alcohol
  • Thirst
  • Cramps
  • Constipation

How Many Liters of Water Daily?

Indeed, water needs vary depending on the outside temperature, the situation (pregnant or breastfeeding women, engaging in sports, etc.), or even the location: at high altitudes, for example, the needs are higher.

According to Professor Yosuke Yamada, "the current recommendation is not scientifically valid at all." Moreover, he notes, "this recommendation does not take into account the food consumed during the day and its water content."

So, how much water should we consume each day? To answer this, scientists studied the water consumption of a cohort of 5,604 people, ranging from one week to 96 years old, in 23 different countries. To calculate the amount of water used, the liquid was marked with an isotope, deuterium. This is a natural isotope of hydrogen. With this element, scientists could determine how quickly water left the body by tracing it, which is a way to estimate the amount of water needed by the body.

However, the figure obtained cannot be directly translated into water consumption. As noted by Professor John Speakman, "even if a man in his twenties has a water turnover of about 4.2 liters per day, he does not need to drink 4.2 liters per day."

What is the Right Amount of Water to Drink Each Day?

Nonetheless, researchers were able to estimate how much water an organism needs. It would be around 3.6 liters of water per day, on average. But as explained earlier, it is not necessary to drink this amount of water.

Indeed, a significant portion of water is provided by food, so it is only necessary to drink between 1.3 and 1.8 liters of water per day to ensure adequate daily intake. According to their calculations, researchers refined their results and estimated that a "typical middle-aged man might need to drink about 1.6 to 1.8 liters of water per day, and a typical middle-aged woman around 1.3 to 1.4 liters."

For Professor John Speakman, "this study shows that the suggestion that we should all drink eight glasses of water — about two liters per day — is probably too high for most people in most situations." He concludes by suggesting that many people should simply follow "what their body tells them."

Risks of Over-Hydration and Dehydration

Excessive hydration can lead to a disruption of the body's balance, known as hyperhydration. The sodium-to-water ratio in blood plasma is altered. Excess hydration can lead to hyponatremia: a decrease in sodium concentration in the overly large volume of water. Cells can become waterlogged and unable to function properly. In some cases, neurological disorders can occur, and in more extreme cases, this can lead to coma or even death.

It should be noted that the kidneys can filter between 1 and 1.5 liters of water per hour.

In cases of dehydration, extreme fatigue can be felt, muscle pain can appear, as well as dizziness. Cardiac activity is slowed, blood pressure drops, and kidney failure may be diagnosed.

What Are Hydrating Beverages?

Water remains one of the essentials for hydrating the body. For some, it may be difficult to get used to drinking plain water. A few drops of lemon or slices of cucumber can help flavor it. Coconut water, rich in electrolytes, can be an interesting alternative to stay hydrated.

Conversely, drinks that dehydrate include coffee and tea, which are known for their diuretic properties. They promote the elimination of water and salts through urine. Alcohol, sugary drinks, sodas, fruit juices, and energy drinks should also be limited or avoided for hydration.

Sources:

Yamada Y, Zhang X, Henderson MET, Sagayama H, Pontzer H, Watanabe D, Yoshida T, Kimura M, Ainslie PN, Andersen LF, Anderson LJ, Arab L, Baddou I, Bedu-Addo K, Blaak EE, Blanc S, Bonomi AG, Bouten CVC, Bovet P, Buchowski MS, Butte NF, Camps SG, Close GL, Cooper JA, Cooper R, Das SK, Dugas LR, Eaton S, Ekelund U, Entringer S, Forrester T, Fudge BW, Goris AH, Gurven M, Halsey LG, Hambly C, El Hamdouchi A, Hoos MB, Hu S, Joonas N, Joosen AM, Katzmarzyk P, Kempen KP, Kraus WE, Kriengsinyos W, Kushner RF, Lambert EV, Leonard WR, Lessan N, Martin CK, Medin AC, Meijer EP, Morehen JC, Morton JP, Neuhouser ML, Nicklas TA, Ojiambo RM, Pietiläinen KH, Pitsiladis YP, Plange-Rhule J, Plasqui G, Prentice RL, Rabinovich RA, Racette SB, Raichlen DA, Ravussin E, Redman LM, Reilly JJ, Reynolds RM, Roberts SB, Schuit AJ, Sardinha LB, Silva AM, Sjödin AM, Stice E, Urlacher SS, Valenti G, Van Etten LM, Van Mil EA, Wells JCK, Wilson G, Wood BM, Yanovski JA, Murphy-Alford AJ, Loechl CU, Luke AH, Rood J, Westerterp KR, Wong WW, Miyachi M, Schoeller DA, Speakman JR; International Atomic Energy Agency (IAEA) Doubly Labeled Water (DLW) Database Consortium§. Variation in human water turnover associated with environmental and lifestyle factors. Science. 2022 Nov 25;378(6622):909-915. doi: 10.1126/science.abm8668. Epub 2022 Nov 24. PMID: 36423296.

L'eau dans l'organisme, CNRS

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