Name a drink that can make you more alert for late-night studying, prevent you from fainting after giving blood, and even promote a teensy bit of weight loss.
Chances are you didn't say water. But that's the right answer.
Researchers at Vanderbilt University Medical Center have shown that ordinary water without any additives does more than just quench thirst. It has some other unexpected, physiological effects. It increases the activity of the sympathetic fight or flight nervous system, which raises alertness, blood pressure and energy expenditure.
David Robertson, M.D., and colleagues first observed water's curious ability to increase blood pressure about 10 years ago, in patients who had lost their baroreflexes the system that keeps blood pressure within a normal range.
The observation came as a complete surprise, said Robertson, professor of Medicine, Pharmacology and Neurology.
"We had to unlearn the idea that water had no effect on blood pressure, which is what all medical students had been told until the last couple of years."
Although water does not significantly raise blood pressure in healthy young subjects with intact baroreflexes, the investigators found that it does increase sympathetic nervous system activity and constrict blood vessels (which prevents pooling of blood in the extremities).
These findings prompted the American Red Cross to conduct a study of water drinking as a method for reducing fainting responses. The study found that drinking 16 ounces of water before blood donation reduced the fainting response by 20 percent.
"This response to water may turn out to be very important for retaining blood donors," Robertson said. "If you pass out after giving blood, you pretty much never give blood again. If we can reduce fainting by 20 percent, we can reduce the unpleasantness of passing out and really bolster the number of people who can continue to be blood donors."
Julia McHugh, a student in Va
|Contact: Leigh MacMillan|
Vanderbilt University Medical Center