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How Much Water Should You Drink and Why?
The human body needs six nutrients to function properly: carbohydrates, proteins, fats, minerals, vitamins and water. Approximately 60% of the body is comprised of water. Muscle tissue alone is 70% water. The body requires a constant supply of water, as all bodily functions depend on, and are influenced by, the balance of body water. The body needs water for heart function, regulation of body temperature, blood pressure, metabolic functions of all cells, and lubrication of the joints. Fluids are needed in the blood to transport glucose to working muscles and eliminate metabolic by-products. In essence, vital functions of the body are seriously compromised when an individual is dehydrated. Dehydration is defined as the loss of fluid from all of the body's fluid compartments. It occurs when the rate of fluid lost is greater than the rate of fluid replaced and is most prevalent during physical activity, especially in hot weather. Without adequate fluid intake, a progressive increase in core temperature perpetuates muscle fatigue and risk of heat illness. Symptoms of dehydration can range from a mild headache, sluggishness to more serious complications. Elevated body temperatures, high heart rates, inability to sustain aerobic exercise intensities, and mental confusion may characterize this form of fatigue associated with dehydration(3). Fatigue may occur even if the body has lost 1 percent body weight due to water loss. Three percent weight loss in water will hinder performance, coordination and develop into heat related illness(3). Even for the person who enthusiastically participates in power walking or jogging, a feeling of fatigue could occur. A common reaction to consuming water is to wait until one is "thirsty". This is an erroneous misconception, as the body is already dehydrated by the time the sensation of thirst is apparent. The sensation of thirst is triggered by a high concentration of sodium (a part of salt) in the blood. When one sweats, water is lost from the blood. So the remaining blood becomes more concentrated with sodium. In hot, humid conditions, the blood vessels near the skin open to facilitate the transfer of body heat to the environment, so the body’s internal temperature is maintained. This causes a reduction in stroke volume (the amount of blood ejected by the heart per beat) and venous return. At any given pace, heart rate will increase, and elevate higher than normal, as the cardiovascular system attempts to maintain cardiac output to meet the oxygen demands in the muscles. When a person is dehydrated, the circulatory system is significantly burdened and cannot meet the demands of the body. As a result, blood volume decreases and the heart must work harder to dissipate internal heat produced from exercise. Scientists have discovered that the total amount of water lost each day is approximately two liters in sedentary adults in cool environments. Although the daily minimum requirement is about 8-10 cups, just to maintain body functions, regular exercise and hot/humid weather compound the need to increase fluid intake. The following table reflects how physical activity and environment affect daily fluid intake:
To consume this much water on a daily basis may be an overwhelming task. Although the amounts seem like a lot, remember a large soda bottle is 2 liters, or 1 gallon = 3.3 liters. It is recommended to ingest fluids throughout the day as the process of rehydration can be a slow process. To ease the "load", the American College of Sports Medicine (ACSM) published a position on the importance or reducing or preventing dehydration during physical activity. The following recommendations are important and every attempt should be made to follow them for adequate hydration. Fluid Intake Before Exercise or the Big Event "Individuals should drink adequate fluids during the 24 hours prior to an event, especially during the time that includes the meal prior to activity, to promote proper hydration before exercise or competition. It is recommended that individuals drink about 17 ounces of fluid about 2 hours before exercise to promote adequate hydration."(2) Meal times are very important as this provides a perfect opportunity to consume fluids. Fluid Intake During Exercise "Athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating, or consume the maximal amount that can be tolerated."(2) Although this statement pertains to the highly fit individual, water consumption is equally as important even for someone who power walks or cycles. Fluids should also be cooler than ambient temperature as this ensures rapid absorption through the stomach into the body. If an event is greater than an hour long then sports drinks, such as Gatorade, are recommended. If not, good old fashion water is best. Fluid Intake After Exercise It is very difficult to completely replace all of the water lost during exercise while one is performing. Generally speaking, people lose between one half and one and a half liters of sweat in an hour of exercise. In most instances, the average person is dehydrated when they finish exercising. Although most of the guidelines pertain to those who participate in intense exercise, the need to rehydrate after exercise is crucial for both physical and mental recovery for all levels of activity. A general recommendation is to consume 8-10 ounces every 15 minutes after exercise. To thoroughly rehydrate, fluid ingestion should exceed that lost through exercise. How about Coke, Pepsi or a beer for a thirst quencher? They have no nutritional value except 150 calories of refined sugar. This sugar does refuel the muscles with carbohydrates, but the natural sugars in juices do the same trick. Juices also replace the potassium lost in sweat and offer vitamin C, a nutrient that promotes healing. Sports drinks such as Gatorade, Max or Exceed also are sugar laden beverages that offer very little nutritional value. They are good to drink during a long workout because of the lower carbohydrate levels are easier to absorb, but after exercise juice and water are your best choices. Remember, alcohol is a diuretic, stimulating water loss. Hydration is important and all individuals engaging in exercise, at all intensities, should work to increase their water intake. You will be amazed how much better you will perform just by drinking more water. Drink, drink and drink some more! References
This article represents a chapter from "Executive Wellness: A Guide for Senior Leaders", an online book written and edited by staff and contributors at the U.S. Army Physical Fitness Research Institute (USAPFRI), U.S. Army War College, Carlisle Barracks, Pennsylvania.
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| Sponsored by the Army National Guard, and the Office of the Chief, Army Reserve. Copyright 2010 |
Sunshine, heat and humidity... the lazy, hazy days of summer. These conditions present a challenge deserving the utmost care and preparation to ensure safety for all who exercise during these months. It is quite common to hear from the most avid exercisers the amount of fluid ingested is minimal, at best. A pot of coffee, a cup of juice or even a beer and off we go! Most individuals function in a dehydrated state and are unaware of the importance of adequate hydration. Both performance and general well-being are intimately associated with an adequate supply of water, as are all functions of the body.