At 94, John Goodenough has invented a glass-based battery that may over-perform the powering of our smartphones, laptops and all other rechargeable electronic devices. Mother Teresa, then 69, received the 1979 Nobel Peace Prize for her humanitarian work among the needy. Diana Nyad swam from Cuba to Florida at age 64.

The list of achievers over 50 and their accomplishments in the world is miles long. What keeps these prolific individuals engaged and excited in their second half of life?

The answer lives within each one of us. Purpose!

Purpose is the reason you wake up in the morning. It directs you to a fulfilling and meaningful life beyond what you may have imagined. Purpose defines your lifework and why you exist and energizes you to be involved in life’s many blessings. Instead of feeling lost, you are involved in using your abilities, experience and talents in meaningful ways.

Your purpose fills you with passion. It gets you moving toward your goals. It pushes you forward on days that aren’t your best because you know there is something important for you to accomplish. You are on a mission and it far outweighs some setbacks you may experience along the way.

Having a personal purpose is like having a master plan for your life. It takes your goodness of heart into the world to make a difference. The payback in satisfaction is incredible. In fact, activating your personal purpose is a powerful, nonmedical prescription for enjoying a healthy, long and happy life.

Purpose Extends Life and Delays Alzheimer’s

Disease Purpose also appears to have a potent ability to improve and extend lives. “It’s a very robust predictor of health and wellness in old age,” said Patricia Boyle, a neuropsychologist at the Rush Alzheimer’s Disease Center in Chicago.

Following almost 1,000 people (average age: 80) for up to seven years, Dr. Boyle’s team found that the ones with “high purpose” scores were 2.4 times more likely to remain free of Alzheimer’s than those with low scores. They also were less likely to develop mild cognitive impairment, often a precursor. “It slowed the rate of cognitive decline by about 30 percent, which is a lot,” Dr. Boyle added.

In addition, her study showed that purposeful people were less likely to develop disabilities or die. A sample of 1,238 people followed for up to five years (average age: 78) by Rush researchers found that those with high purpose had roughly half the mortality rate of those with low purpose.

The Elixir of Having a Life

People who are purposeful have goals, activities and interests that direct their days and make time on this planet pleasurable. At the same time, they usually experience enormous satisfaction in helping others.

By activating your purpose, you may become one of the stories about people who do amazing things when they are inspired to action—because you are living on purpose. By helping yourself, others and the world, you will make the contributions for which you were born to give.