Hydration: How Much Should You Drink Daily?

We sometimes read that we should drink eight glasses daily, or approximately 2 liters of water, to maintain good hydration. But what is it?

Water Is An Essential Liquid For Our Life

Our body comprises a significant portion of water, representing 75% of birth weight and decreasing to around 55% in older people. A water deficit of 20% is enough to put our lives in danger.

A Water Balance Conditioned By Water Intake And Elimination Processes

The amount of water present at any given time in our body depends on fluid intake and loss. On the intake side is the water we drink directly, in pure form or drinks. Added to this is the water content of our foods, such as fruits and vegetables, which are particularly rich. It is estimated that 20 to 25% of our daily water intake comes from food.

The chemical reactions within our body can also generate the precious H 2 O molecule, which will be added to the available stock. Several processes contribute to water loss: breathing, perspiration, and the release of water with urine and stools. Their level varies according to our characteristics (sex, body size, etc.), climatic conditions, or level of physical activity.

The Consequences Of Dehydration

The body’s degree of hydration is a crucial parameter for our well-being, on which our intellectual and physical performance depends.

Dehydration Disrupts Performance And Perceptions

A study conducted at the University of Connecticut by Professor Armstrong among 25 young women, for example, showed that dehydration of only 1.36% during a sports session leads to an alteration in mood, an increase in the perception of difficulty associated with completing a task, problems concentrating, and headaches. A fluid status that is not optimal impacts endurance capacities and reduces strength and power during sports activities.

Hydration Is An Essential Parameter In Weight Control

Furthermore, drinking enough is crucial for controlling your weight. Obese or overweight adolescents have lower water intake than adolescents of average weight. Consuming a good amount of water facilitates weight loss as part of a slimming diet.

Dehydration Impacts The Health Of Many Organs

A lack of hydration could also have consequences on our cardiovascular health. Data suggests that it causes inflammation, interferes with the functioning of blood vessels, and disrupts blood pressure regulation, potentially promoting high blood pressure. A team from the American National Heart, Lung, and Blood Institute in Bethesda, Maryland (United States) studied the consequences of chronic water deficiency throughout life in mice. Researchers have found that deprivation of the precious fluid promotes inflammatory phenomena and blood clotting and accelerates the appearance of damage in different organs: heart, kidneys, and brain. Ultimately, this results in a reduced life expectancy for these animals.

A Sophisticated Mechanism Regulates Thirst

Faced with the risks that dehydration represents for our body, the latter has a complex network of messengers, hormonal for some, to prevent it. The objective is twofold: trigger the feeling of thirst to encourage us to replenish the stock and limit losses as much as possible. Thirst corresponds to the signal emitted by our body to tell us it needs liquid. It occurs when blood osmolality, which reflects its particle concentration, increases. This means that the blood is too concentrated; in other words, there is not enough fluid to dilute it.

Vasopressin Helps Save Water In The Body

Specialized cells in the hypothalamus (a gland in the brain) will then stimulate the release of vasopressin, the antidiuretic hormone. The quantity of vasopressin released is more significant as the blood is concentrated in particles. It acts directly on the kidney, telling it to reduce water loss by concentrating urine. Furthermore, the lack of water in the body reduces blood volume; this drop is detected by sensors in the wall of blood vessels, which relay the message to the brain to trigger vasopressin secretion.

The Body Reacts And Adapts To The Variation In Blood Volume

The kidneys also have sensors capable of detecting this drop in blood volume, which govern the release of an enzyme, renin, into the blood. It allows the formation of angiotensin I, itself transformed into angiotensin II, which will adapt the diameter of the blood vessels to the flow of blood by reducing their caliber.

This also causes an increase in the level of aldosterone in the blood, limiting sodium losses from the kidneys and controlling the release of vasopressin. These mechanisms, therefore, make it possible to reduce water loss and signal to us that it is high time to drink. A loss of 1% of water increases the concentration of solutes in the blood, triggering the feeling of thirst. Drinking dilutes the blood and increases the blood volume in the vessels, which slows the release of the various actors mentioned. The feeling of thirst temporarily disappears.

Should You Drink Before You Are Thirsty?

However, some assure us that we should drink before feeling thirsty because it would already be too late when we think of this signal. The scientific data does not support this belief but confirms the well-established mechanism. Researchers have, for example, shown that when we have access to water, we drink spontaneously before our body suffers from the consequences of fluid loss. In healthy people, it is therefore advisable to drink when you feel the need rather than complying with a more or less well-founded recommendation. The situation becomes complicated in certain situations where the mechanisms regulating hydration fail.

Older Adults At Risk Of Dehydration

Dehydration is a widespread problem among seniors. Indeed, during aging, several phenomena add up and threaten water balance. A research team from Johns Hopkins University in Baltimore (United States) has shown that after 24 hours of water deprivation, older men feel the sensation of thirst less intensely than young men. The signal emitted by the body to encourage drinking is, therefore, more tenuous in older people and more accessible to ignore.

On the other hand, the kidneys lose their ability to prevent fluid elimination through urine, even if it runs out. Vasopressin becomes less effective with aging. Lack of hydration among the elderly could have very harmful consequences; some specialists hypothesize its responsibility in the occurrence of dementia associated with Alzheimer’s disease, for example.

Certain Illnesses Or Trauma Cause Loss Of Sensation Of Thirst Or Adipsia

Outside of aging, the loss of the sensation of thirst (a symptom called adipsia) can manifest itself in certain pathological situations. It occurs when the hypothalamus, the conductor that controls appetite, is damaged due to head trauma, brain disease (a tumor developing in this region of the brain, for example), or as a result of a surgical intervention. In these circumstances, it becomes essential to force yourself to drink at regular intervals to avoid becoming dehydrated.

A Thirst Impossible To Quench: Polydipsia

On the contrary, in certain circumstances, an intense thirst is felt (called polydipsia). Diabetes insipidus, a disease associated with a failure in vasopressin secretion, typically causes excessive thirst. However, in rare cases, it is accompanied by losing this sensation. Diabetes often causes intense thirst if left untreated, a sign that often leads to the discovery of the disease. A kidney or hormonal condition, brain damage, and taking certain medications (antidepressants, anticholinergic medications, etc.) are all factors that can contribute to increasing thirst.

Does Drinking Too Much Water Pose Health Risks?

If a lack of water threatens our health, consuming too much of it can be just as harmful:

Hyponatremia: Excessive Dilution Of Sodium In The Blood

Excessive hydration can lead to hyponatremia, a situation where the sodium level in the blood drops below a certain threshold. This then causes headaches, nausea and vomiting, cramps, convulsions, loss of consciousness, etc. In the most severe cases, hyponatremia can lead to death. This situation is rare because the kidneys can evacuate water only up to a certain point. It is estimated that the maximum filtration capacity of the kidneys in a healthy adult is 800 ml to 1 L per hour.

Certain Situations Can Lead To Water Intoxication

Hyponatremia causing mild symptoms can appear after consuming 3 to 4 liters of water per day. More severe signs occur with greater intakes, mainly if concentrated over a short time. In children, the filtration capacity of the kidneys is not optimal, and hyponatremia can occur more quickly. We encounter this situation of water intoxication in people suffering from psychiatric disorders, sometimes in the context of abuse or during specific medical treatments. But also athletes engaged in prolonged efforts. Drinking more than you are thirsty to compensate for all water losses does not improve sports performance and can even cause gastric problems.