Drinking only half of the recommended eight glasses of water a day may result in mild dehydration, a small study of college students has found.
The preliminary study may add credence to the notion that most people would do well to gulp down at least eight 8-ounce glasses of water each day, lead researcher Dr. Wayne Askew of the University of Utah in Salt Lake City told Reuters Health.
"For people who aren't exercising a lot or living in a very warm climate, eight glasses of water a day may be a good rule of thumb," said Askew.
Those who are exercising and sweating more than normal need to replenish the essential liquid to avoid dehydration, according to the Utah researcher.
The findings were presented last week at the annual Experimental Biology meeting in San Diego, California.
In the 12-week experiment, Askew's team monitored the hydration status and well being of 10 college students. Over the course of the study period each student drank four, eight or 12 eight-ounce glasses of water per day in four-day test cycles. Between tests the students stuck to their normal water consumption and during one other week, they did the same, Askew explained.
At the end of each water consumption cycle, all of the students underwent a battery of tests that assessed their body's hydration status. They also answered questions about their general well being.
When students consumed only four glasses of water, their blood plasma volume – a measure of hydration – was five percent below those who drank eight glasses of water, who had normal blood plasma volume, explained Askew.
In addition, drinking only four glasses of water was associated with more highly concentrated urine.
"The levels of dehydration associated with four glasses of water were mild – what we refer to as a suboptimal hydration level," said Askew.
Although the health effects of drinking less water were mild, the researchers did notice a difference in student's well being. When students drank the least amount of water, they reported feeling less energetic and less focused than when they drank more water.
Drinking 12 glasses of water caused blood plasma volumes to be 10 percent above levels measured when the students drank eight glasses of water. Attitudes of well being did not differ between those who drank eight glasses of water compared to those who drank 12 glasses of water, according to Askew.