By DR. MARIA ALICE
LIFE TAKES place in an aqueous solution. The cells, the basic “bricks” that “construct” the human body, are mostly made of water, as is the blood that brings the nutrients and oxygen to them and the interstitial fluid bathing them. Each day, water and salt are lost and replaced. The kidneys process the body fluids thus regulating the fluid volume and its composition, so that the stability of the internal milieu is maintained.
Water is the body’s principal component, it accounts for approximately half of an adult human’s body weight. Because fat contains little water, individuals with more body fat have less body water. On average, total body water constitutes 60 per cent of lean body weight in young men, 50 per cent in young women and older men, and 45 per cent in older women. Two-thirds of the body water is intra-cellular (inside the cells) and the remainder is contained outside the cells in the extra-cellular fluid compartment, which includes the intra-vascular plasma (the liquid inside the blood vessels) and the interstitial fluid, in the tissues, “bathing” the cells. Small amounts of water are also contained in bone, dense connective tissue that forms a kind of net maintaining the cells in place, digestive secretions, and cerebrospinal fluid.
How much water should you drink each day?
A simple question with no easy answers. Based on several studies, many varying recommendations have been produced over the years, but, in truth, water needs depend on many factors, including health conditions, levels of activity and even where one lives, the climate.
Though no single formula fits everyone, knowing more about your own body’s specific needs for fluids will help to estimate how much water to drink each day.
Water is lost every day through the breath, perspiration, urine and bowel movements. The water supply must be replenished by consuming beverages and foods that contain water, so that the body will function properly.
Water needs for the average, healthy adult living in a temperate climate are calculated as follows:
A litre of water is lost each day through breathing, sweating and bowel movements and the average urine output for adults is 1.5 litres a day, giving a total of approximately 2.5 litres. As 20 per cent of the total fluid intake comes from food, consuming two litres of water or other beverages a day, along with your normal diet, will typically replace the lost fluids. Thus the total consumption per day should be roughly 3.0 litres.
What factors influence
the water needs?
The total fluid intake needs to be modified depending on:
• Exercise. The more you exercise, the more fluid you will need to keep the body hydrated. The amount of additional fluid needed depends on how much sweat was lost during the exercise, but around two to three cups an hour will generally be adequate, if the weather is not exceptionally warm.
Fluid should be replaced after exercise and, during long and intense exercise, it is better to use a sports drink containing sodium, as this will help replace sodium lost in sweat, which could be life threatening.
• Environment. Hot or humid weather can make you sweat and requires additional intake of fluid. During wintertime the heated indoor air also can cause the skin to lose moisture. Further more, altitudes greater than 2,500 metres (8,200 feet) use up more of the fluid reserves by triggering increased urination and more rapid breathing.
• Illnesses or health conditions. Fever, vomiting and diarrhoea, cause the body to lose additional fluids so you should drink more water and may even need oral rehydration solutions. Certain conditions, including bladder infections or urinary tract stones, also require increased water intake but, on the other hand, other conditions such as heart failure and some types of kidney and liver diseases may impair excretion of water and even require the fluid intake to be limited.
• Pregnancy or breast-feeding. Women who are expecting or breast-feeding need additional fluids to stay hydrated. Especially when nursing, women lose large amounts of fluid. Pregnant women should drink around 2.5 litres (about 10 cups) of fluids daily and women who breast-feed should have 3.0 litres (around 12.5 cups) of fluids a day.
Are there other sources of water beyond the tap?
It is a great idea to keep water within reach at all times, there is no need to rely only on what you drink to satisfy your own fluid needs. What you eat also provides a significant portion of the fluid needs. Food provides, on average, around 20 per cent of total water intake. Water and all kinds of beverages will supply the remaining 80 per cent.
Many fruits and vegetables, such as watermelon and cucumbers, are nearly 100 per cent water and beverages such as milk and juice are mostly comprised of water as well. Even if they should not be a major portion of your daily total fluid intake, beer, wine and caffeinated beverages such as coffee, tea or soda can contribute. Nevertheless, you must be careful with these as they trigger excessive water loses. Water being calorie-free, inexpensive and readily available is, without any doubt, the best bet.
What are the health benefits of water?
• Regulates body temperature
• Moistens tissues such as those in the mouth, eyes and nose
• Lubricates joints
• Protects body organs and tissues
• Helps prevent constipation
• Lessens the burden on the kidneys and liver by flushing out waste products
• Helps dissolve minerals and other nutrients to make them accessible to the body
• Carries nutrients and oxygen to cells
And the list could go on. Every system in the body depends on water to function. Water flushes toxins out of vital organs, carries nutrients to the cells and provides a moist environment for the ear, nose and throat tissues.
What are the signs and complications of dehydration?
Dehydration is a consequence of not taking enough water to replace the amount that was used by the body, and thus there is not enough water in the body to carry out the normal functions. Even mild dehydration, as little as a one to two per cent loss of your body weight, can sap your energy and make you tired. As we said above, common causes of dehydration include strenuous activity, excessive sweating, vomiting and diarrhoea.
Signs and symptoms of dehydration are:
• Mild to excessive thirst
• Dry mouth
• Little or no urination
• Muscle weakness
Although mild dehydration rarely results in complications as long as the fluid is replaced quickly, more-severe cases can be life threatening, especially in the very young and the elderly. If that is the case, fluids or electrolytes may need to be delivered intravenously.
How to stay safely hydrated
It is not generally a good idea to use thirst alone as a guide for when to drink. By the time one becomes thirsty, it is possible to be already slightly dehydrated. Furthermore, be aware that when getting older the body is less able to sense dehydration and send brain signals of thirst. Excessive thirst and increased urination can be signs of a more serious medical condition and it is advisable to talk to your doctor if you experience either.
Nearly every healthy adult can consider the following:
• Drink a glass of water with each meal and between each meal.
• Hydrate before, during and after exercise.
• Substitute alcoholic drinks for sparkling water at social gatherings (do your best …).
When drinking water from a bottle, remember that only bottles designed for reuse should be refilled.
If you are concerned about your fluid intake, check with a doctor or a registered dietician so that they will help to determine the amount of water that is best for you.
To avoid dehydration and to make sure the body has enough fluids for its needs, make water your beverage of choice.
Best health wishes, Dr. Maria Alice
Consultant in General and Family Medicine
Director – Luzdoc International Medical Service