Story highlights Barbara Bush acknowledged in 1989 she had been diagnosed with Graves' disease

Bush, 88, was admitted to the hospital Monday, a family spokesman said

"She is in great spirits," the spokesman said

The former first lady was hospitalized in 2008, 2009 and 2010 for various ailments

Former first lady Barbara Bush has been hospitalized in Houston, Texas, for treatment of a "respiratory-related issue," a family spokesman said Tuesday.

Bush, 88, was admitted Monday at Methodist Hospital, spokesman Jim McGrath said in a written statement.

"She is in great spirits, has already received visits from her husband and family, and is receiving fantastic care," the statement said. "Updates will be issued when warranted."

CNN was first alerted to Bush's hospitalization by tweets from affiliate KPRC

Her husband, George H.W. Bush, was the 41st President of the United States. He also served as vice president for two terms under President Ronald Reagan.

In her role as first lady, she championed the cause of literacy. She formed the Barbara Bush Foundation for Family Literacy in 1989.

That was the same year that she acknowledged she had been diagnosed in 1988 with Graves' disease, an autoimmune disease that commonly affects the thyroid.

In 2010, she was hospitalized for what doctors at the time described as a recurrence of Graves' disease.

Bush underwent heart surgery in 2009 after doctors found hardening in one part of her aorta.

In 2008, she was hospitalized after suffering abdominal pain. She underwent surgery for a perforated ulcer.