Alzheimer’s disease may be becoming an epidemic.

The number of U.S. cases has increased to 5 million from 4.5 million in the past 5 years, according to David Shenk, author of “The Forgetting. Alzheimer’s: Portrait of an Epidemic.”

With the oldest boomers approaching age 65, that number could mushroom to 15 million by 2011, Shenk warned during a teleconference sponsored by a foundation affiliated with MetLife Inc., New York.

“Alzheimer’s affects not only the patient but also caregivers,” Shenk said. “It can take people’s lives over for a decade or more.”

Results of a recent survey sponsored by MetLife show that many Americans are unrepared for Alzheimer’s disease.

Although 35% of participants said they knew someone with Alzheimer’s disease, 74% of the participants admitted to knowing little or nothing about the disease.

Meanwhile, although 80% of older survey participants said preparing for the possibility of getting Alzheimer’s disease is important, only 26% have considered care options, and 83% have made no financial arrangements, according to the survey results.