FOOD, MEDICINE, & HEALTH

Hyperhydration—Can Too Much Fluid Hurt?
Bottled water is a big competitive business, with retail sales reaching nearly $9 billion in 2004. It has emerged as the No. 2 beverage in the United States, behind soft drinks. Consumers and athletes pay a premium for splashes and fortified and flavored waters in their quest to remain hydrated as part of the apparent health and wellness movement.

The Food and Drug Administration regulates the quality of bottled water, and the Environmental Protection Agency regulates the quality of tap water from municipal sources.

With regard to nutrition—and in the context of the enormous advertising and consumer push for "pure" water at the desk, in the gym, or on the track—symptoms of hyperhydration (too much water) and hyponatremia (not enough sodium) are on the rise. The potential health risks of drinking too much fluid with insufficient sodium before and during exercise are being reassessed by leading exercise physiologists, the American College of Sports Medicine, the National Athletic Trainers Association, team physicians, and sports nutritionists.

In a 2004 report, "Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate," the Institute of Medicine’s Food and Nutrition Board warned that physically active people should avoid drinking too much water, which in extreme may result in hyponatremia, a condition which occurs when the blood sodium level falls below normal (<135 meq/L). It is a clinically important concern among some of our "healthiest" consumers.

The FNB report (www.nap.edu/openbook/0309091691/html/) suggests that high levels of dietary sodium may contribute to or exacerbate several clinically important conditions, such as hypertension and diabetes. At the same time, it is important to realize that disturbances in total body sodium content affect extracellular volume, and that perturbations in total body water affect serum sodium concentration. Thus, the significance of maintaining the balance of water and electrolytes, especially sodium, in plasma and the body’s tissues cannot be understated, particularly when advising those involved in extensive physical activity.

A pathological model for this condition of hypervolemic (expanded blood volume) hyponatremia is manifest in some endurance athletes, military personnel, hikers, and weekend exercisers with congestive heart failure. These individuals may have an increased total body sodium content and total body water content due essentially to decreased kidney blood flow (renal perfusion). These same individuals may also become hyponatremic because of the "functional" underfilling of their arterial circulation, which stimulates vasopressin secretion from the hypothalamus; this stimulates thirst and a powerful urge to drink, which in turn leads to water retention and reduced urine volume induced by antidiuretic hormone secreted by the pituitary gland. These events override the negative feedback effect of the body’s osmoreceptors that normally act to decrease vasopressin secretion in response to hyponatremia.

The risk of hyponatremia is significant in healthy endurance and weekend athletes involved in low-intensity exercise who may overhydrate in response to a belief that tremendous water intake is generally protective. This situation seems especially salient among those with slower pace (>4 hr) in running events such as marathons and triathlons. Symptoms of severe, acute hypervolemic hyponatremia typically encompass central nervous system parameters, including but not limited to lethargy, confusion, agitation, and even seizures. As these symptoms may mimic frank dehydration, some athletes mistakenly conclude that plain bottled or tap water may be the most desirable approach to rehydration. Nothing could be further from the truth—too much fluid can hurt!

Hyperhydration, which contributes to hyponatremia, is an emerging concern among trainers and health care professionals and a condition that can be prevented. Adequate consumption of properly formulated and clinically tested electrolyte-containing beverages as part of a fluid-replacement regime during exercise and endurance events can prevent or reduce the risk of hyponatremia and related sequelae, while maintaining fluid balance and important physiological functions.

ADDITIONAL READING
Grandjean, A.C. and Campbell, S.M. 2004. "Hydration: Fluids for Life." ILSI North America, Washington, D.C. www.ilsi.org/publications/pubslist.cfm?publicationid=556.

Flinn, S.D. and Sherer, R.J. 2000. Seizure after exercise in the heat. Recognizing life-threatening hyponatremia. Physician Sportsmed. 28(9). www.physsportsmed.com/issues/2000/09_00/flinn.htm.

BY ROGER CLEMENS, Dr.P.H.
Director, Analytical Research
Professor, Molecular Pharmacology & Toxicology
USC School of Pharmacy, Los Angeles, Calif.
[email protected]

BY PETER PRESSMAN, M.D.
Internal Medicine
Geller, Rudnick, Bush & Bamberger
Beverly Hills, Calif.
[email protected]