Silicon Valley's newest status symbol is a humble piece of furniture.

A growing number of workers at Google Inc., Facebook Inc. and other employers are trading in their sit-down desks for standing ones, saying they feel more comfortable and energized. They also are motivated by medical reports saying that sitting for too long leads to increased health risks.

A standing desk sits high off the floor so a worker can either stand at it or sit on a high stool to use it. Officials at Palo Alto-based Facebook say a number of employees asked about standing desks after news articles were published about the health risks of sitting all day.

The stories cited medical studies that tied excessive sitting to increased obesity and other health problems because of factors including a drop in physical activity. A 2010 study by the American Cancer Society found that women who sat more than six hours a day were 37% more likely to die prematurely than women who sat for less than three hours, while the early-death rate for men was 18% higher. The American College of Cardiology released a study in January that found increased mortality among people who sat longer at home than those who didn't.

No one seems to compile statistics on the standing-desk trend. But anecdotal reports suggest Silicon Valley is embracing the movement.

Facebook officials say they have seen an upsurge in requests for standing desks to five to eight a week with a total of between 200 and 250 deployed at the company of more than 2,000 employees. Facebook also is trying out a treadmill station─where a worker can walk or run on a treadmill while tapping at a computer.

Google spokesman Jordan Newman said that 'many employees at Google opt for standing desks, and we offer them as part of our wellness program' though he said he didn't know the exact number.

Greg Hoy, 39 years old, asked for a standing desk shortly after joining Facebook seven months ago as a design recruiter. 'I don't get the 3 o'clock slump anymore,' he said. 'I feel active all day long.'

Tiffani Jones Brown, 29, said she also requested a standing desk when she joined Facebook two months ago as a content strategist, in part to keep her energy level high. 'I get really tired when I sit all day,' Ms. Jones Brown said.

There is a learning curve to using standing desks, however. Ms. Jones Brown said that at first it was hard for her to concentrate on writing tasks because she was focused on things like maintaining correct posture. Other stand-up workers use tricks to not be bothered by being on their feet most of the day. 'I kind of move my legs around, no real position,' said Kirk Everett, one of two standing workers in the 21-employee offices of the Silicon Valley Leadership Group in San Jose, a tech industry trade association.

Mr. Everett is a pioneer in standing desks, having gotten one seven years ago to help recover from a back injury. He said he could never go back. 'It is so much better,' said Mr. Everett, vice president of government relations for the trade group. 'Staying seated all day is your enemy.'