Dehydration occurs when the body loses so much fluid that it no longer functions at optimal levels. People with diabetes are at risk for dehydration because high glucose (blood sugar) levels in the bloodstream trigger dehydration. This occurs because the kidneys cannot absorb excess glucose and must expel it by forming increasing amounts of urine, which deprives the body of fluids.

Other causes of dehydration include:

• Fluid loss as a result of vomiting, diarrhea, excessive urination (polyuria) or sweating
  
  
• Inadequate fluid intake
  
  
• A combination of fluid loss and insufficient fluid intake

Dehydration can be classified as mild, moderate or severe. The determination is based on the percentage of body weight lost during an acute illness. This includes:

• Mild dehydration. A loss of 3 to 5 percent of body weight.
  
  
• Moderate dehydration. A loss of 6 to 9 percent of body weight.
  
  
• Severe dehydration. A loss of more than 10 percent of body weight. Severe dehydration is a life-threatening condition that demands immediate medical attention.

Dehydration is particularly dangerous in young children, who have a high body surface area relative to body size and weight. For this reason, children lose a lot of fluid through the skin as they perspire. Children are at additional risk of dehydration because they:

• Have high metabolisms that quickly turn over the water and electrolytes (substances within water important for good health) they consume, further contributing to the risk of dehydration.
  
  
• Have kidneys that are not as efficient at conserving water as those of adults.
  
  
• Have immune systems that are more vulnerable than an adult’s. This increases the risk of contracting illnesses that cause symptoms (such as vomiting and diarrhea) that promote dehydration.
  
  
• Do not always drink enough water when they are ill.
  
  
• Depend on caregivers to provide them with food and fluids.

Children who experience a surge in glucose levels can become dehydrated quickly. In infants, dehydration can set in within several hours.

Older adults are also at high risk of dehydration because they may have:

• Decreased thirst sensation, which sometimes keeps them from drinking as much as they should
  
  
• Kidneys that do not work efficiently
  
  
• Physical problems such as arthritis that may make it difficult for them to drink
  
  
• Medications that increase the risk of dehydration
  
  
• Problems such as incontinence or physical incapacitation that may cause them to intentionally limit fluid intake to decrease trips to the bathroom
  
  
• Impairments in memory or other cognitive functions that can cause them to forget to drink enough water

Two conditions that can affect diabetic individuals when glucose levels rise – diabetic ketoacidosis and hyperosmolar hyperglycemic nonketotic syndrome (HHNS, also called nonketotic hyperosmolar state) – can also involve or trigger dehydration.

Dehydration can also play a role in other disorders, including kidney stones and gout, both of which are more prevalent in diabetes patients than in nondiabetics.

The dehydration associated with type 1 diabetes, type 2 diabetes and other forms of diabetes mellitus should not be confused with an unrelated endocrine condition called diabetes insipidus. This is a rare condition in which the kidneys are unable to conserve water. This leads to increased urination and excessive thirst. 

Though it is important to drink enough water and avoid dehydration, consumption of too much fluid can also cause health problems. Overhydration, where the body loses less water than it takes in, causes insufficient levels of sodium in the blood (hyponatremia). Extreme cases of overhydration, or water intoxication (regularly drinking more than 2 gallons or 7.6 liters a day), can cause tissue damage, confusion, seizures, coma and even death.

Dozens of studies indicate that, generally, men need an average of 125 ounces (3.7 liters) and women 91 ounces (2.7 liters) a day, according to the Institute of Medicine, which advises moderating consumption of sodium rather than overhydrating. Individuals who are very active physically or live in hot climates may need to drink more.