Former President George H.W. Bush remained at a Houston hospital on Monday for the seventh straight night after being admitted for shortness of breath, but an aide said the 41st president's breathing "has returned to normal."

Bush, 90, had been taken by ambulance to Houston Methodist Hospital on Tuesday evening as a precaution, family spokesman Jim McGrath said last week.

"Both President and Mrs. Bush wish to thank everyone for their good wishes and prayers," McGrath said in a statement.

Bush spent Christmas 2012 in intensive care at the same hospital while being treated for a bronchitis-related cough and other issues. He was discharged in January 2013, after nearly two months in the hospital.

Bush is the oldest living former American president. He suffers from a form of Parkinson's disease that has forced him to rely on a motorized scooter or wheelchair. But he's also skydived on at least three of his birthdays since leaving the White House, including a tandem jump for his 90th birthday in June.

Bush made two public appearances last month. He attended an event at Texas A&M University with his son, former President George W. Bush, and served as the coin-toss captain for the Houston Texans during a Nov. 23 game that honored the U.S. Armed Forces.

The elder Bush was a naval aviator in World War II -- at one point the youngest in the Navy -- and was shot down over the Pacific.

Bush served two terms as Ronald Reagan's vice president before being elected the nation's 41st president in 1988. After one term, highlighted by the success of the 1991 Gulf War in Kuwait, he lost to Democrat Bill Clinton amid voters' concerns about the economy.

The Associated Press contributed to this report.