BAKERSFIELD, Calif. -- As the baby boomers become senior citizens, aging -- and how to do it well -- is a topic that preoccupies individuals and health officials alike.

More than 5 million Americans have Alzheimer's disease -- a figure that is set to double every 20 years.

Maintaining a healthy diet and getting regular exercise are both habits that may cut the risk for mental decline, and new research has found that merely having a purpose in life could help as well.

Researchers from Rush University studied 900 older adults for seven years. They found those who had purpose in their lives had a slower rate of mental decline and were more than twice as likely to remain free of dementia.

People who felt their lives had meaning set goals for themselves. They did not feel that all their accomplishments were behind them and they enjoyed being active.

Doctors said the next step is to test whether people can be given a sense of purpose -- by helping them focus on their contributions and outlining new goals.