Chapter 13: Water and Electrolytes
13.4 Consequences of Water Deficiency or Excess
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program
As with all nutrients, having too much or too little water has health consequences. Excessive water intake can dilute the levels of critical electrolytes in the blood. Water intoxication is rare, however when it does happen, it can be deadly. On the other hand, having too little water in the body is common. In fact, diarrhea-induced dehydration is the number-one cause of early-childhood death worldwide. In this section we will discuss subtle changes in electrolytes that compromise health on a chronic basis.
High-Hydration Status: Water Intoxication/Hyponatremia
Water intoxication mainly affects athletes who overhydrate. Water intoxication is extremely rare, primarily because healthy kidneys are capable of excreting up to one liter of excess water per hour. However, if the rate of water consumption exceeds the kidneys’ ability to remove the excess, serious complications can arise. Overhydration was unfortunately demonstrated in 2007 by Jennifer Strange, who drank six liters of water in three hours while competing in a “Hold Your Wee for a Wii” radio contest. Afterward she complained of a headache, vomited, and died.
The symptoms of water intoxication are caused by dilution of sodium in the body (hyponatremia), and so will be discussed in more detail in section 13.5.
Low-Hydration Status: Dehydration
Dehydration refers to water loss from the body without adequate replacement. It can result from either water loss or electrolyte imbalance, or, most commonly, both. Dehydration can be caused by prolonged physical activity without adequate water intake, heat exposure, excessive weight loss, vomiting, diarrhea, blood loss, infectious diseases, malnutrition, electrolyte imbalances, and very high glucose levels. Physiologically, dehydration decreases blood volume. The water in cells moves into the blood to compensate for the low blood-volume, and cells shrink. Signs and symptoms of dehydration include thirst, dizziness, fainting, headaches, low blood-pressure, fatigue, low to no urine output, and, in extreme cases, loss of consciousness and death. Signs and symptoms are usually noticeable after about 2 percent of total body water is lost.
Chronic dehydration is linked to higher incidences of some diseases. There is strong evidence that low-hydration status increases the risk for kidney stones and exercise-induced asthma. There is also some scientific evidence that chronic dehydration increases the risk for kidney disease, heart disease, and the development of hyperglycemia in people with diabetes. Older people often suffer from chronic dehydration as their thirst mechanism is no longer as sensitive as it used to be.
Heat Stroke
Heat stroke is a life-threatening condition that occurs when the body temperature is greater than 105.1°F (40.6°C). It is the result of the body being unable to sufficiently cool itself by thermoregulatory mechanisms. Dehydration is a primary cause of heat stroke as there are not enough fluids in the body to maintain adequate sweat production, and cooling of the body is impaired. Signs and symptoms are dry skin (absence of sweating), dizziness, trouble breathing, rapid pulse, confusion, agitation, seizures, coma, and possibly death. Dehydration may be preceded by heat exhaustion, which is characterized by heavy sweating, rapid breathing, and fast pulse. The elderly, infants, and athletes are the most at risk for heat stroke.
Water intoxication occurs when more water is taken in than is needed or than can be excreted. Excessive water intake can dilute the levels of critical electrolytes in the blood, and can be fatal.
Malnutrition refers to one not receiving proper nutrition and does not distinguish between the consequences of too many nutrients or the lack of nutrients, both of which impair overall health.
Signs refer to readily observed identifying characteristics of a disease such as swelling, weight loss, or fever. Symptoms are the subjective features of a disease recognized by a patient and/or their doctor.
“heart disease” refers to several types of heart conditions. The most common type is coronary artery disease, which can cause a heart attack. Other kinds of heart disease may involve the valves in the heart, or the heart may not pump well and cause heart failure.
Hyperglycemia is when blood glucose levels are higher than normal. Hyperglycemia is usually associated with diabetes, but it can occur in response to medications or other health conditions.
Heat exhaustion occurs when dehydration decreases blood volume to a degree that cooling the body is no longer possible. Symptoms include heavy sweating, rapid breathing, and disorientation.