PRESCRIPTIONS
Drinking water in excess can be harmful
By Landis Lum
Q. My wife drinks 8 glasses of water a day. Is this really worth doing?
There is no evidence that drinking extra water is better for you — that it helps you lose weight or improves health.
If you have certain heart, liver, or kidney diseases, or are on certain drugs, such as water pills for hypertension, extra water may actually be harmful, excessively diluting your blood and causing tiredness or overloading your circulatory system.
In a study last year published in the journal Nutritional Neuroscience, drinking extra water before a hot pasta lunch did not reduce food intake, whether done immediately or 30 minutes before eating. There is no evidence that drinking extra water prevents or treats urine infections.
What about drinking extra fluids with colds and coughs? The highly regarded Cochrane Database research group states that although drinking extra fluids has been recommended to replace losses from fever or evaporation and perhaps thin the mucus, there are reasons why drinking extra fluids may be harmful.
Anti-diuretic hormone (ADH) is produced in extra amounts with various lung infections (bronchitis, bronchiolitis and pneumonia caused by either viruses or bacteria).
ADH reduces a kidney's ability to get rid of extra water, and drinking extra liquids when you have a bad cough may then lead to excessive dilution of your blood or even fluid overload.
The Feb. 28 issue of the British Medical Journal described a study in children with pneumonia where four kids had such severe dilution of their blood they died.
But you should drink extra water if you've had kidney stones, or have fluid losses from vomiting, diarrhea, sweating on hot-and-humid days, prolonged exercise, or other causes. Two articles published almost a year apart (Nov 25, 2003, and Nov 26, 2002) in the journal Circulation found that drinking 16 ounces of water raises blood pressure enough to help keep people from fainting.
Drinking this amount does not increase blood volume by more than 1 percent, but does improve blood vessel tone. So if you faint during blood tests, blood donations, prolonged standing, or heat exposure, just drink 16 ounces of water beforehand — the protection lasts about 40 minutes.
Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at UH-Manoa's John A. Burns School of Medicine. Send your questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; or write islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.
