Anyone can become dehydrated if they lose too many fluids. But certain people are at greater risk, including:

  • Infants and 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.
  • 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, dementia, 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, such as kidney disease and heart failure, also make you more likely to become dehydrated. 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 may lose more water than it can absorb. With every hour you exercise, 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 above 8,200 feet, or about 2,500 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 — the faster you breathe to maintain adequate oxygen levels in your blood, the more water vapor you exhale.
  • People working or exercising outside in hot, humid weather. When it's hot and humid, your risk of dehydration and heat illness increases. That's because when the air is humid, sweat can't evaporate and cool you as quickly as it normally does, and this can lead to an increased body temperature and the need for more fluids.
Feb. 12, 2014