How good would it feel if someone just gave you $1,000?
Last fall, Oprah Winfrey thrilled audience members with these words: "You will each go home with $1,000."
Then she said there was a catch: "You have to spend the money on someone other than your family."
Winfrey said she wanted them to experience how good it feels to give.
They still applauded, but the smiles looked a little forced.
Yet maybe she did her audience a favor, because even though the audience had to give the money away, it could get back even more than they gave.
Stephen Post explains why in his new book, "Why Good Things Happen to Good People."
He reveals that new science shows giving -- money or time -- not only feels just as good as getting, but can actually improve your health.
"Giving is as good for the giver as it is for the receiver. Science says it's so. We'll be happier, healthier, and even -- odds are -- live a little longer if we're generous," Post said.
"Public health isn't just about bugs and staying away from lead. It's about doing unto others, and at the right dose, science says it's very good for you," he said.
Arthur Brooks, author of the new book, "Who Really Cares: The Surprising Truth About Compassionate Conservatism," also knows a lot about the current research on charity.
Brooks said, "There's evidence that it helps people with their asthma, in cardiovascular disease, weight loss, insomnia. When people have a lot of happiness, they do a lot better in their health as well."
That was true for former heart patients at Duke University Medical Center.
They were asked to visit current heart patients -- no particular agenda, just to listen and lend support. By doing that, the volunteers had better health after their heart attacks.
A similar study at the University of Miami by Dr. Gail Ironson followed HIV patients who volunteered, like Katherine Marshall Scott, who talks to teenagers about avoiding infection, and Stephen Baker, who counsels fellow HIV survivors.
These and other HIV patients who helped others had lower stress levels and higher immune resistance.
Scott's disease-fighting cells went up, from 200 to 800.
Baker says he could feel how volunteering improved his health.
"To get involved with someone else's problems makes your problems look a lot less," he said.
At least five studies show that seniors who gave tended to live longer, Post said.
After senior Fred Dekuyper started volunteering at a school, a small miracle happened.
"I used to walk with a cane all the time, and now I don't need the cane anymore," he said.
Many high schools require their students to volunteer.
It's called service learning. And oddly, even though the charity is forced, it still brings happy results. Teachers say students who volunteer raise their grades, and get higher SAT scores.
Abington High School student Jeff Rohrback said, "After service learning started, I got so involved into it, I started paying attention more, picked up my grades."
So "20/20" decided to see whether we could find a similar effect.
We put an ad on Craigslist recruiting people who were not currently volunteers. We introduced them to Post, and asked them to try it for one week.
But first, Post had them fill out a questionnaire that asked how they felt about life, like how often during the week they felt calm and peaceful.