Dr. David Robertson and colleagues at Vanderbilt University Medical Center in Tennessee showed water -- without additives -- has unexpected, physiological effects. It increases the activity of the sympathetic, "fight or flight," nervous system, which raises alertness, blood pressure and energy expenditure, they said.
Robertson and his research team first observed water's ability to increase blood pressure about 10 years ago.
"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," Robertson said in a statement.
The study found water does not significantly raise blood pressure in healthy young subjects with intact baroreflexes -- a negative feedback system that buffers short-term changes in blood pressure.
The study, published in the journal Hypertension, found because water raises sympathetic nervous system activity -- and consequently energy expenditure – it promotes weight loss, Robertson explains.
"I calculated it might be as much as 5 pounds a year if you drank three 16-ounce glasses of water a day and nothing else changed," Robertson said.
"It's interesting that activation of the sympathetic system is enough to do that."