Water and Human Body

Water: The Only Liquid the Body Needs

To live a fully healthy and functional life, water is indispensible. From the point in history when primitive species moved from the oceans to land, a major factor of survival has continually been stopping dehydration. The important adaptations that enable this are present in almost all species of animals, including man. Water makes up varying percentages of the body weight of humans from 75% in infants, to about 55% in the elderly, and is crucial for maintenance of cellular homeostasis (Popkin, D'Anci and Rosenberg). Even though humans can survive a couple of weeks without eating, the human body cannot last even a few days devoid of water (Student Nutrition awareness campaign). Even slight dehydration can disturb physiological functions resulting in headaches, exhaustion, dryness of the mouth, and even muscle weaknesses and mental deterioration, according to Heller (Reinberg).

When talking about body fluids we are basically discussing water. Tight maintenance of the delicate balance existing between the intake and output of water, and its circulation, is essential for optimal performance of all the organ systems in the body. Disruptions to this delicate balance do occur and they must quickly be identified and rectified for the return to normal body fluid homeostasis (Gwinnutt and Thorburn).

Everything that will be covered in this paper concerns pure drinking water which is the perfect beverage without any calories. It is also easily available and is not expensive. Water is the single most important fluid that is required by our bodies because it is the main component of all other fluids in the body.

Other sub-topics covered in this paper include water volume and the constituents in the body, the benefits to the human body, and how dehydration affects the body. A conclusion is also given.

Water

Water makes up about 55-65% of the body weight. It is essential for the optimal function of all body cells. The human blood is made of 83% water while the muscles, brain and bones are made up of 75%, 74% and 10% water, respectively. Water distributes nutrients to the entire body through blood, and it helps eliminate waste via carrying it away from the cells. In the form of sweat, water helps to regulate the body temperature. Water is critical for digestion and the optimal performance of organs. It also lubricates joints (Student Nutrition awareness campaign).

The total amount of water present in the body is affected by various factors including age, sex, and definitely the weight of the individual. For an adult male, about 60% of his total body weight is made up of water; for example, a healthy hydrated man who weighs 75 kilograms will be made up of about 45 liters of water. This water is known as the total body water (TBW). Total body water is scattered throughout the whole body and can be imagined as being contained in different body compartments or spaces (Gwinnutt and Thorburn). The spaces are separated from one another by membranes, which regulate the circulation of water among different spaces; this determines the amount of water that can be present in each of the spaces. The largest body fluid 'space' which makes up two thirds of the total body water (30 L) is within the body cells and is known as the intra-cellular fluid (ICF). The balance of one third (15 L) is found outside the cells of the body and is known as extra-cellular fluid (ECF). The ECF is further separated into different compartments; 10 liters are distributed between the body cells and this is known as interstitial fluid (ISF), 3.5 liters of ECF forms blood plasma in the circulatory system and is known as intra-vascular fluid (IVF), and the balance of 1.5 liters makes up trans-cellular fluid, which comprises cerebrospinal fluid (CSF), intraocular fluid, urine and the fluid in the bowel's lumen (Gwinnutt and Thorburn).

Most individuals don't take in enough water; this results in several disturbing symptoms that cause pain including headaches, loss of consciousness, back pain, pain in the joints, and kidney stones (Tennesen).

Benefits of water to the body

Drinking water is essential for many activities in the body. The benefits of water to the body include

• Distribution

Blood, 83% of which is water, is the body's distribution or transport system that enables the supply of oxygen, nutrients, enzymes and minerals that promote optimal functioning of the body cells. Blood also plays a crucial role in eliminating waste products by carrying them away from the organs to other sites.

• Lubrication

The presence of water in the fluids between internal organs and between the joints enables easy movement via the reduction of friction within the body. This allows the body to easily move when walking.

• Digestion

The mucous lining the digestive tract is mostly made up of water and enables food to slide through the tract enabling its digestion. The salivary juices also contain water, which enables the movement of digestive enzymes to break down food.

• Temperature control

For optimal body functions, it is essential that the human body temperature is maintained within a narrow range. Water generally changes temperature by enabling the movement of heat. Therefore water in the body can not only store this heat but also move it to regulate temperature. Perspiration is another way in which water controls body temperature. This is because through sweat, heat is moved out of the body. One can lose almost a pint of water daily via the evaporation of water from sweat.

• Synthetic reactions

Within the human body there are many chemical and biological reactions that build enzymes and hormones which regulate various reactions in the body. Most of these reactions involve water.

• Waste removal

Upon the consumption of nutrients and oxygen, most of the cells ultimately produce waste products. Water enables the removal of these waste products by transporting them to kidneys and then out of the body through urine. Waste products are also removed through perspiration.

Water Intake and Sources

As human beings we ingest water as the normal plain drinking water, as beverages, and also in food. Water in food could be natural, from the food itself, or it could be added when cooking. It could also be produced in the process of metabolism. Many foods have water that is inherent: fruits and vegetables are made of 75-95% water; poultry, meat and fish are 50-65% water; while breads are about 35% water (Student Nutrition awareness campaign). All these different foods add up to the total water intake. Total water intake includes: water that is ingested in foods and beverages, and that which is produced in the process of metabolism of food which is approximately 350-400 mL/d (Grandjean). A sufficient intake of water is essential particularly for those who lead active lifestyles, because they lose substantial amounts of water through perspiration. Throughout exercise one should consume several glasses of water. It is also recommended that one should make a habit of drinking water throughout the day at regular intervals, even if one does not feel thirsty (Student Nutrition awareness campaign). Indeed, it has been shown that, by the time an individual 'feels thirsty', they are already in a state of 'mild dehyration'. As well, for those who are concerned with weight loss, another interesting factor is that 'feelings of hunger' may rather be signals that the body needs water.

However several medical journals released recently state that there isn't enough scientific evidence to back the claim that taking glass of water (with a capacity of eight ounces), eight times a day can bring about many benefits such as increasing the rate of weight loss, removal of toxins, healing dry skin, reducing fatigue or even speeding up the recovery rate from flu (Beck).

Intake and Output of Water and Electrolytes

To guarantee the best performance of all body functions it is important that the total body water is maintained within the desired volume, which is greatly determined by age, weight and sex among other factors. The distribution of the required amount of water to various 'compartments' is also important. How the body ensures that the fluid balance is maintained at the desired level is a process known as homeostasis. In a healthy body, waters (and by extension electrolytes contained in them) are constantly being lost. These have to be replaced to ensure that equilibrium homeostasis is maintained (Gwinnutt and Thorburn).

There are situations where the amount of water lost in the body is significantly increased e.g. when one suffers burns or has diarrhea. These can result in undesired distribution of body fluids resulting in inadequate or excess amounts in some of the compartments, for example, post- operative sepsis.

For a 75 kg man who is fully healthy, every day he will have a water output of about 2.5 liters; therefore an intake of equal amount is needed for maintenance of homeostasis (Gwinnutt and Thorburn). There are two kinds of fluid loss, sensible and insensible. Sensible fluid loss is that which can be observed and quantified, for example urine output; insensible fluid losses cannot easily be observed and quantified, and may include sweat or water vapor exhaled (Gwinnutt and Thorburn).

Sweat

How much one sweats is one of the factors controlled by the hypothalamus of the brain. It does so in response to fluctuations of both body and skin temperatures. Sweat can lead to a significant loss of body fluids because it varies greatly, from highs of about 8000 mL a day, to the 'normal' of about100 mL. The electrolyte content that is lost in sweat also varies and is dependent on the diet, exercise, mood, and hereditary conditions e.g. cystic fibrosis (Gwinnutt and Thorburn). As well, different ethnic groups and individuals may sweat more or less; some individuals have relatively impaired 'sweat capacity', and are thus more susceptible to heat.

Urine

The amount of urine produced, and its content can also greatly vary. These two are usually determined by the amount and composition in the IVF 'space'. It also depends on the condition of the kidney. The composition of IVF is determined by several factors such as fluid intake, body and ambient temperature and significant fluid losses from the body. The fact that urine must be produced daily is due both to solute intake, and the generation of waste products such as urea and creatinine during metabolism; thus the need for excretion. These products also determine the concentration of urine that the human kidneys can produce (Gwinnutt and Thorburn).

Respiratory Tract

When one exhales, the gases contain only water vapor and no solutes. Normally about 400 mL of water is lost in a 24-hour period. This loss can be more if you breathe in non-moist oxygen or have even a slight increase in the rate of breathing such as during exercise. Though not medically significant when considered in isolation, it is important that one develops a habit of reducing these losses when possible e.g. By breathing in warm moist air (Gwinnutt and Thorburn).

Evaporative Losses

Apart from sweating, a further 400 mL of body fluid is lost through evaporation from the skin. The main difference between the two is that evaporative loss only involves plain water with zero electrolyte content, and thus has a minimal clinical significance.

Adverse Consequences of inadequate water intake

To achieve optimal performance of body functions it is quite important that you have a total fluid intake of about 16 cups (eight oz) of water if male and 12 if female. It is important to note that the total fluid intake includes that which is found in food and beverages. Because it is not possible to count water in foods, thirst should act as a natural indicator alerting you that your body needs water. One should make it a habit to drink water consistently at certain intervals in the course of the day. Another natural indicator that can alert one of the body's need for water is the loss of weight (Student Nutrition awareness campaign).

One of the most adverse effects of insufficient water intake is dehydration. The symptoms of dehydration differ based on the level of water deficit. For example, when the loss of fluid is at 1% of the body weight, this disrupts thermo-regulation and thirst also occurs at this level. The feeling of thirst goes up at 2% dehydration; at about 3% dehydration, dry mouth can be observed. It is also at 2% that mild discomfort and the loss of appetite occurs. At a dehydration level of about 4%, it has been observed that productivity at work is reduced by up to 30% (Grandjean). Difficulty in concentration, headaches, and sleepiness occur at 5% dehydration. Itchiness and the loss of sense in the extremities can be observed at 6% dehydration, and collapse occurs at about 7% dehydration level. A 10% loss of body fluid can result in death (Adolph, as cited in Grandjean). For example, during the War of 1967 between Egypt and Israel, over 20,000 Egyptian soldiers are said to have died from severe heat stroke. The Egyptian army was at that point enforcing stringent water rationing. Israeli troops, on the other hand, had sufficient water supplies in the battle field that minimized the number of heat casualties (Stewart, as cited in Grandjean).

Physiological Effects of Dehydration

The importance of water in the health of the body is ascertained in terms of variations from normal (the ideal state of hydration). The term dehydration in this paper includes both the act of losing body fluids and the state of dehydration itself.

Physical performance

The importance of water, and by extension, hydration, in the course of physical activity, especially in athletes and in military activities, has been of interest to many and is well documented in much of the scientific literature. During difficult athletic activities, it is normal for athletes to lose up to 10% of their body weight in the form of sweat; this has led to dehydration of the body if the fluids lost are not replaced. However decrease in athletic performance has been noted even at minimal levels of dehydration such as 2% (Popkin, D'Anci and Rosenberg). At these lower levels of dehydration, athletes participating in challenging athletic events will experience a decrease in performance that is linked to increased fatigue, disrupted thermo-regulation, decreased endurance, and an escalation in perceived effort. Replenishing the lost water can reverse these effects, and further diminish oxidative stress which is brought about by intense physical activity. It has also been observed that dehydration has a higher impact on intense exercises and endurance activities, such as lawn tennis and long distance running, as compared to anaerobic exercises such as lifting of weights (Popkin, D'Anci and Rosenberg).