Durham, N.C. — Duke University's endowment has lost more than $1 billion in the last five months, Duke President Richard Brodhead said in an e-mail sent late Wednesday to faculty and staff.

Stock market volatility, depressed real estate prices and other economic troubles cost the endowment 19 percent of its value between July 1 and early December, Brodhead said.

The endowment was valued at $6.1 billion as of June 30, according to Duke Management, which oversees the fund. A 19 percent loss would be equal to $1.15 billion.

Proceeds from the endowment account for about 15 percent of Duke's annual operating budget, Brodhead said, noting that he has asked deans and administrators to plan for possible budget cuts.

"We need to regard this as a time of challenge, not of retreat," he wrote in the e-mail. "When leaner times come, a family cuts back on less-essential expenses and concentrates on what matters most. That is what Duke must do now, and I ask for your cooperation as we do it."