Anyone can become dehydrated if the loss of fluids outweighs fluid intake. But certain people are at greater risk, including:
Infants and children. Worldwide, dehydration caused by diarrhea is a leading cause of death in children. Infants and children are especially vulnerable because of their relatively small body weights and high turnover of water and electrolytes. They're also the group most likely to experience diarrhea. In the United States, diarrhea remains one of the most common childhood illnesses.
Older adults. As you age, you become more susceptible to dehydration for several reasons: Your body's ability to conserve water is reduced, your thirst sense becomes less acute and you're less able to respond to changes in temperature. What's more, older adults, especially people in nursing homes or living alone, tend to eat less than younger people do and sometimes may forget to eat or drink altogether. Disability or neglect also may prevent them from being well nourished. These problems are compounded by chronic illnesses such as diabetes, by hormonal changes associated with menopause and by the use of certain medications.
People with chronic illnesses. Having uncontrolled or untreated diabetes puts you at high risk of dehydration. But other chronic illnesses also make you more likely to become dehydrated. These include kidney disease, cystic fibrosis, alcoholism and adrenal gland disorders. Even having a cold or sore throat makes you more susceptible to dehydration because you're less likely to feel like eating or drinking when you're sick. A fever increases dehydration even more.
Endurance athletes. Anyone who exercises can become dehydrated, especially in hot, humid conditions or at high altitudes. But athletes who train for and participate in ultramarathons, triathlons, mountain climbing expeditions and cycling tournaments are at particularly high risk. That's because the longer you exercise, the more difficult it is to stay hydrated. During exercise, your body can absorb about 24 to 32 ounces of water an hour, but you may lose twice that amount in hot weather. With every hour, your fluid debt increases. Dehydration is also cumulative over a period of days, which means you can become dehydrated with even a moderate exercise routine if you don't drink enough to replace what you lose on a daily basis.
People living at high altitudes. Living, working and exercising at high altitudes (generally defined as 8,000 to 12,000 feet, or about 2,400 to 3,600 meters) or very high altitudes (12,000 to 18,000 feet, or about 3,600 to 5,400 meters) can cause a number of health problems. One is dehydration, which commonly occurs when your body tries to adjust to high elevations through increased urination and more rapid breathing â€” the faster you breathe to maintain adequate oxygen levels in your blood, the more water vapor you exhale.