A big swig of water might keep you on your feet, according to new research.

Drinking about 16 ounces of water may help prevent healthy people from fainting due to standing or after donating blood, according to two reports presented Thursday at the American Heart Association's 56th Annual High Blood Pressure Research Conference.

"Prolonged standing, especially in a warm environment, leads to occasional fainting, even in healthy people," said Dr. Christoph Schroeder, of Humboldt University in Berlin, Germany. "Our results show that drinking water right beforehand improves the ability to stand and may help prevent fainting."

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Both groups studied healthy people without a history of fainting to follow up earlier research at Vanderbilt University in Nashville, Tenn. That research had shown that drinking water reduced the likelihood of fainting in people with malfunctioning autonomic nervous systems.

Such people are prone to pass out when they stand up. The autonomic nervous system regulates body functions that are not consciously controlled, including heart rate and blood pressure.

"As we considered that finding, it occurred to us that there is a big problem with people passing out after giving blood," said Dr. David Robertson, of Vanderbilt University, senior author of the other report. "We believe that around 150,000 people a year faint or experience near-fainting after blood donations, and many of those people never give blood again."

Both teams conducted their research using tilt-table testing. In that test, a person lies on a bed-like platform parallel to the floor. The bed is then tilted upward so the head is above the feet. The people were tilted to a 60 degree angle, two-thirds of the way between lying flat and standing upright.

"You might think you could lie at that angle all day," Robertson said. "But most people can't stay at that angle beyond 45 minutes without passing out."

In the Vanderbilt study, drinking a 16-ounce glass of water five minutes before tilting made participants able to tolerate the tilt longer. Those who drank water had a smaller decrease in heart rate associated with tilting than those who didn't drink.

The German team found that participants who drank 16 ounces of water 15 minutes before tilting held off fainting about five minutes longer than those who didn't drink water. The researchers also found that drinking water tended to lower the heart rate while lying down, and improve the force and flow of blood in the body both when horizontal and upright.