Water is essential for life and conditions practically all the biological functions of the human being. Our body is made up of 60% water, but more precisely this percentage increases to 70% in the brain, 80% in the blood and 90% in the lungs. Without this fluid, the pumping of blood, thinking and breathing would be impossible, so life itself could in no way be reached.
On average, man loses about 2.3 liters of water per day, the value of which is divided into the following values: urine is responsible for the release of 1 to 1.5 liters, sweat 0.3 to 0 , 9 (depending on physical activity), breathing about 0.4 liter and faeces 0.1-0.2 liter. Even the exhaled air is essential for maintaining the body’s water balance, as we lose around 350 milliliters of this fluid with a vapor-like exhalation.
As you can see, we are an open system that is losing water, heat, and organic matter all the time. For this number of reasons, you need to maintain a constant supply of nutrients and water, but do you know how much water to drink per day? Here we give you an answer, taking into account the science and research raised recently.
The body and the water
Osmolarity is a measure used to express the total concentration of substances in solutions, with the parameter osmoles / liter. Osmolality, on the other hand, uses osmoles / kilogram of liquid values, but in dilute solutions (such as fluid media in the human body) the two terms can be used interchangeably with convenience.
People with a plasma osmolarity between 285 and 295 mOsm / kg are considered hydrated, regardless of the level of urine produced and water consumption.. The brain directly modulates the two vital functions according to the concentration of body fluids, so knowing the osmolarity of the blood plasma is “enough” to be able to estimate the condition of a patient at a given moment.
The most common formula for establishing plasma osmolarity (osmolality) is:
OSMp = 2[Na+] + [glucosa] + [urea]. Normal = 290 ± 10 mOsm / kg H2O
This formula it includes the 3 most common solutes in blood plasma, which are sodium, glucose and urea. The normal range of sodium levels in the blood is 135 to 145 milliequivalents per liter, while glucose is considered correct when the value is below 5.6 mmol / L: beyond this, prediabetes is studied / diabetes. On the other hand, urea, the end product of protein metabolism, is present in plasma ranges of 12 to 54 mg / dl.
All these values depend on the percentage of solutes present in the plasma, but also on the water available to the body, because we remember that 80% of the blood is water. The more water we have available in the body, the more diluted a sample can be, within normal limits.
How much water should I drink per day?
Based on this detailed but necessary introduction, it should be noted that what is really important is the osmotic balance in our body, beyond the arbitrary values in liters of water, with regard to the intake. A person can lose up to 1% of their body weight in sweat during strenuous exercise, so naturally the water intake will have to be much higher than that of another person who has not moved from the sofa. all day.
However, there are a number of mean values that can be established in the general population. The European Food Safety Authority made a list in 2010, with the consumption of milliliters of water per day, in different age groups. The average values are as follows:
- Newborns 0-6 months: 680 milliliters per day, as breast milk.
- Children from 6 to 12 months: from 800 milliliters to 1 liter per day.
- Children from 4 to 8 years old: 1600 milliliters per day (1.5 liters).
- Boys aged 14 to 18: 2.5 liters per day.
- Girls aged 14 to 18: 2 liters per day.
- Adults: 2 to 2.5 liters per day.
As you can see, the values vary greatly according to the age group analyzed and also according to the government sources consulted. It can be concluded that most men need 2.5 to 3 liters (depending on demand and physical activity), while women need a little less, 2 to 2.5 liters. This distinction is purely arbitrary, simply based on the fact that men tend to have slightly higher muscle mass.
The brain and its role in hydrating the body
Studies such as water intake, water balance, and elusive daily water requirements (Nutrients Journal) have attempted to accurately quantify the importance of these numbers at the neuroendocrine level. The brain is constantly working to maintain the internal homeostasis of the body, so expect the plasma concentration of hormones and neurotransmitters to vary depending on the physiological needs at any given time..
With this idea in mind, the levels of vasopressin circulating in patients at different times of the day were quantified. This hormone is the primary regulator of body fluids, is produced in the hypothalamus, and is stored and released by the neurohypophysis. It causes vasoconstriction, reabsorption of water in the kidneys and acts, among other things, as an antipyretic / analgesic.
The intensity of the neuroendocrine response (using circulating vasopressin levels as a parameter) has shown that typical brain mechanisms for dehydration begin to activate on average when the person consumes less than 1.8 liters of water per day. .
Outraged, up to 71% of adults consume less than this Daily Value in some countries, showing slight signs of dehydration throughout the day. These values show that the majority of the population does not respect the minimum Total Daily Water Intake (TWI L / 24H) so that neuroendocrine defense methods do not appear in the face of dehydration.
How do you know if you are drinking little water?
The normal oscillation of water in the body during a day is less than 2% of the patient’s body weight. For that, Hypohydration is clinically defined as a condition in which a person loses more than 2% of their weight per day as a result of this condition.. Dehydration (the next step in the clinical event) is considered when the loss of body water is greater than 3%.
Dehydration (mild to severe) manifests itself with symptoms such as dry mouth, fatigue, weakness, irritability, dizziness, nausea, headache, constipation, dry skin, and many other events. It can be caused by a lack of water supply, but certain infectious diseases (such as bacterial infections which cause vomiting and profuse diarrhea), hormonal disorders (effects of chronic diabetes) and even organic problems (at the level of liver, kidneys, etc.) can cause dehydration in the patient.
Sometimes avoiding dehydration is a matter of responsibility, while in other cases it is not at all on the disposition of the patient.. People with diabetes who show signs of dehydration or patients with acute infectious intestinal diseases, for example, should go to the emergency room doctor immediately. Sometimes intravenous fluid therapy is the only possible approach to avoid complications.
As you can see, the question “how much water should be drunk per day?” We can answer several things, always keeping in mind the individual condition. First, the intake depends on the age, sex and physiological state of the person, because for example, pregnant women should drink almost half a liter more per day than non-pregnant women.
In general, it is estimated that around 2 liters of daily intake in women and 2.5 in men are sufficient, but the figure can increase much more if we are talking about athletes or people with a body mass index. very high. However, below 1.8 liters of intake, responses neuroendocrine processes associated with dehydration begin to manifest, so this is a clear “cut point” for all functional adults.
- Armstrong, LE and Johnson, EC (2018). Water consumption, water balance and daily dodge water requirements. Nutrients, 10 (12), 1928.
- Liska, D., Mah, E., Brisbois, T., Barrios, PL, Baker, LB and Spriet, LL (2019). Narrative review of selected hydration and health outcomes in the general population. Nutrients, 11 (1), 70.
- Andersson, B. (1978). Regulation of water intake. Physiological Reviews, 58 (3), 582-582.
- Hooton, TM, Vecchio, M., Iroz, A., Tack, I., Dornic, Q., Seksek, I. & Lotan, Y. (2018). Effect of increased daily water intake in premenopausal women with recurrent urinary tract infections: a randomized clinical trial. JAMA Internal Medicine, 178 (11), 1509-1515.
- Vargas-Garcia, EJ, Evans, CEL, Prestwich, A., Sykes-Muskett, BJ, Hooson, J. and Cade, JE (2017). Interventions to reduce the consumption of sugary drinks or increase the consumption of water: evidence from a systematic review and meta-analysis. Opinion on obesity, 18 (11), 1350-1363.