--Leonardo da Vinci
Water constitutes up to 60% of the human adult body. This water serves a number of important functions including:
- Helping to regulate body temperature through sweating
- Assisting in flushing waste out of the body
- Carrying nutrients and oxygen to the body’s cells
- Moistening tissues in the eyes, nose, and mouth
- Lubricating and cushioning joints
In fact, nearly all of the major systems in the body depend on the availability of water. The body has limited capacity for storing water so a continuous supply is required to maintain these functions. When you use or lose more water than you are taking in, dehydration can develop. Some of the causes for dehydration include exercising in the heat, fever, vomiting or diarrhea, and not drinking adequate amounts.
Signs of dehydration: Thirst, the physiological urge to drink water, is a signal that the body is becoming dehydrated. Other signs of mild to moderate hydration include dry or sticky mouth, dark yellow urine, headache and muscle cramps. Severe dehydration may be associated with absence of urination, rapid heartbeat, dizziness, confusion, rapid respirations, and even loss of consciousness.
Dangers of dehydration: Dehydration can lead to serious complications, including:
- Heat injury. Dehydration coupled with high ambient temperatures can lead to heat injury. This can range in severity from mild heat cramps to its most severe form, heatstroke.
- Hypovolemic shock. Since water is the major constituent of blood, dehydration can reduce the volume of circulating blood. The resulting hypovolemia (low blood volume) can the cause a severe drop in blood pressure and oxygen being delivered to the body, a condition known as “shock”.
- Kidney failure. With dehydration and reduced blood flow, the kidneys are unable to remove excess fluids and waste from your blood. This can lead to the accumulation of waste products such as creatinine and urea nitrogen in the body.
- Kidney Stones. Higher temperatures contribute to dehydration, which leads to an increased concentration of calcium and other minerals in the urine that promote the growth of kidney stones.
- Coma or death. If not addressed promptly with measures to rehydrate, severe dehydration can be fatal.
Staying hydrated: The average urine output for adults is 1.5 liters a day. Additionally, people lose almost a liter of water a day through breathing, sweating and bowel movements. Since approximately 20% of our daily fluid requirement is met through the foods we eat, this leaves about 2 liters (or about 8 cups) to get through drinking water and other fluids. This calculation may have led to the recommendation that we need to drink “8 ounces of water (one cup), 8 times a day”. Does this mean that the water requirement for someone working and living in an air conditioned environment is the same as that of a physical laborer working outdoors during the summer? Of course not---individual water requirements are highly variable, depending on a number of factors such as the ambient temperature, activity level and state of health.
For healthy adults in a temperate climate without the additional fluid requirements brought about by exercise, the answer appears to be “let thirst be your guide”. If you drink enough fluid so that you rarely feel thirsty, your fluid intake is most likely adequate without having to count your cups.
With the increased sweating that occur during exercise or working in a hot environment, you’ll need more fluid to keep your body hydrated. For short bouts of exercise, this may just be an extra 1-2 cups but for more intense exercise lasting an hour or more, regular intake is necessary to avoid dehydration. Depending on the ambient temperature, this usually means taking in 2 to 3 cups per hour. With strenuous athletic activity lasting several hours, or if working in the heat, a sports drink containing sodium may even be better than plain water in helping to maintain electrolyte balance.