Washington, May 28: Michelle Obama's office is a challenging workplace, where grueling hours and the expectations of a formidable boss intensify the demands of managing a popular United States First Lady's schedule, image and agenda, sources familiar with the White House's East Wing have said.

"The first lady is a lovely woman, but she's tough as nails, and that can be hard for some people. She has really high expectations," Politico quoted a source, as saying.

The grueling hours are also taking a toll on her staff, as less than three years into the job, Obama is on her third chief of staff and third social secretary.

She is on her second communications director, the White House chief usher recently departed, and her Press secretary Katie McCormick-Lelyveld's last day is next Friday.

Earlier, on Friday afternoon, the first lady's office announced that the executive director of Michelle's signature campaign to fight childhood obesity also is leaving.

Julianna Smoot left the Social Secretary's office to serve as Deputy Campaign Manager for Barack Obama's 2012 re-election campaign.

Robin Schepper, Executive Director of the first lady's "Let's Move!" anti-obesity initiative, is departing after less than a year on the job.

Former First Lady Laura Bush saw a similar churn on her staff - after six years.

By 2007, Bush was on her third press secretary, third social secretary and second chief of staff.

Former First Lady Hillary Clinton had comparatively low turnover during her days in the White House, employing just two chiefs of staff in eight years.

Katherine Jellison, a history professor at Ohio University who specializes in first ladies, believes that Obama is under more scrutiny than other modern first ladies because of being the first African-American first lady.

"She also represents a new generation, really the first post-boomer generation of first lady," Jellison added. (ANI)