In the human body, water represents an essential constituent for the maintenance of life, and it is also the one present in greater quantities.
Its presence is indispensable for the performance of all the physiological processes and biochemical reactions that take place in our body. In addition, water enters the structure of various substances and acts as a solvent for most nutrients (minerals, water-soluble vitamins, amino acids, glucose, etc.), playing an essential role in digestion, absorption, transport and use of the same nutrients. Water is also the means by which the body eliminates metabolic waste, and is essential for regulating body temperature.
In addition, the water acts as a “lubricant” and acts as a shock absorber in the joints and tissues, keeps the skin and mucous membranes elastic and compact (whose functionality depends on the right degree of hydration) and guarantees the correct consistency of the intestinal contents . Given that in practice there is no system within the body that does not depend directly on water, it is easy to understand that maintaining a proper balance of our “water balance” (ratio between the “inputs” and the “outputs” of water) is essential for maintaining good health in the short, medium and long term.
Our body is mainly made up of water. In the newborn, water represents about 75% of body weight. This percentage fraction decreases until adulthood, when it stabilizes around 55-60% of body weight. In the elderly there is a further decrease in the amount of total body water, both as an absolute value and as a percentage fraction. The differences between the sexes are evident starting from adolescence. The woman, in fact, having a higher percentage of adipose tissue (poor in water), has a lower percentage of water.
Approximately 75% of the muscles and internal organs and 10% of the adipose tissue are made up of water. More than 30% of the skeleton itself is made up of water. 66% of the total water present in our body is located inside the cells and determines their volume and turgor. 6- 7% is present in plasma, 2% in lymph and 23-25% is extracellular water, located in the spaces existing between the cells.
Like all the chemicals that make up our body, water is continuously lost and consumed, and therefore must be continuously replenished from the outside. The main means by which our body maintains water balance are the thirst mechanism (which regulates the amount of water to be ingested) and the reabsorption of water in the kidneys (which regulates the amount of water eliminated in the urine). However, the thirst mechanism has a delayed response time, and often occurs only when the loss of water has already been such as to cause the first negative effects. Furthermore, sometimes (particularly in elderly individuals) the thirst mechanism works poorly, and therefore many people risk not adequately and promptly replacing water leaks. The water requirement for adults and the elderly is approximately 1 ml of water for each kilocalorie introduced during the day. For children, who are most at risk of dehydration, the requirement is greater, and corresponds approximately to 1.5 ml / kcal / day.
The center of thirst is located in the brain. With an extremely complex and sensitive mechanism, it collects and processes various signals from different types of receptors located in various parts of the body. In general, the sense of thirst is determined by the dehydration of the nerve cells. Other factors that help increase the sensation of thirst are dry mouth and decreased blood volume. On the other hand, distension of the stomach causes less desire to drink.
The first symptom of dehydration is dry mouth. Then, as the state of dehydration increases, both the skin and the mucous membranes (including those of the eye) become dry and dry and a sense of fatigue, headache, redness of the skin, muscle cramps, loss of appetite appear , intolerance to heat, apathy. If the state of dehydration is even more severe, dizziness, nausea and vomiting, tachycardia, decreased level of attention and concentration and doubling of vision, up to loss of consciousness and risk of coma may occur.
Water does not contain calories, and any short-term change in body weight due to greater loss or greater water retention is deceptive and momentary. Therefore, the attempt to contain weight by rationing water is absolutely useless, as well as being risky for our state of health. Under normal conditions, the daily water losses in the adult individual are around 3-4% of body weight (2-2.5 liters). It is however important to note that these losses are much higher the more the individual is of a young age, with a peak in the first months of life, during which the daily water losses reach 15% of body weight. Consequently, children are another group of population particularly exposed to the risk of dehydration, if the lost water is not adequately and promptly replenished.
Dehydration of only 1% of body weight has an impact on the activity and physical performance of our body. If dehydration rises to 2%, thermoregulation and plasma volume are altered and a sense of thirst begins to manifest. With dehydration around 5%, cramps, weakness, increased irritability appear, while around 7% there may be general malaise, profound weakness and even hallucinations. With 10% there is a real risk of heat stroke onset, and survival itself is beginning to be endangered. A persistent state of dehydration compromises both the physical and mental capacities of our body. It also increases the risk of kidney stones, the risk of contracting colon and urinary tract tumors (bladder, prostate, kidneys) and the risk of prolapse of the mitral valve. The elderly are particularly vulnerable; dehydration in this age group is associated with a general impairment of health.
We lose water through our urine, feces, sweating and breathing. With urine, an average adult eliminates around 1300 ml / day. With feces the loss of water is around 150 ml per day on average. In the average adult, water losses through the exhaled air and through evaporation from the skin (perspiration) and sweating normally amount to about 600-1000 ml / day, depending on the environmental conditions (a temperature increase from 24 to 31 ° C determines the doubling of this quantity), physiological conditions (an increase in body temperature of 2 ° C leads to doubling of water losses through perspiration) and, obviously, the level of physical activity. Sweat is the main mechanism through which our body maintains its thermal balance (evaporation of sweat makes our skin and, consequently, our body cool down).
In Conclusion how to behave:
Always indulge your thirst and indeed try to anticipate it by drinking enough, on average 1.5-2 liters of water per day. Remember also that children are more exposed to risk of dehydration than adults.
Drink frequently and in small quantities. Drink slowly, especially if the water is cold: in fact, a sharp drop in the temperature of the stomach can create conditions for dangerous congestion.
Older people must get used to drinking frequently throughout the day, during and between meals, even when they do not feel thirsty.
The water balance must be maintained by drinking essentially water, both tap water and bottled water, both safe and controlled. Remember that different drinks (such as orange drinks, cola drinks, fruit juices, coffee, tea) as well as providing water also provide other substances that contain calories (for example simple sugars) or that are pharmacologically active (for example caffeine). These drinks should be used in moderation.
It is wrong to avoid drinking for fear of sweating excessively (sweating is essential to regulate body temperature) or gaining weight (water does not provide calories).
During and after physical activity, drink plenty and promptly replenish the losses due to sweating, using mainly water.
In certain pathological conditions that cause a greater loss of water (for example feverish states or repeated episodes of diarrhea), the lost water must be properly and promptly replenished.
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