ST. PETERSBURG, Fla. — Bill Golden survived more than 20 years in the U.S. Army and another 30 in law enforcement. He fell sick with colon cancer, and at 86, he has an artificial hip and arthritis in his knees.

Golden still gives thanks, though, and researchers say that appreciative attitude can be good for you, too.

Academics have long theorized that expressions of thanks promote health and happiness and give optimism and energy to the downtrodden. Now, the study of gratitude has become a surprisingly burgeoning field, and research indicates being thankful might help people actually feel better. There's a catch, however: You have to say thanks more than just once a year.

"If you don't do it regularly you're not going to get the benefits," said Sonja Lyubomirsky, a psychology professor at the University of California, Riverside. "It's kind of like if you went to the gym once a year. What would be the good of that?"

In recent years, researchers have tried to measure the benefits of gratitude. In a National Science Foundation-funded study, Northeastern University psychologist David DeSteno had participants complete an arduous data entry task only to have it lost by computer malfunction. Then, a lab assistant, seemingly unconnected to the study and claiming to be in a hurry for their own experiment, restores the lost work.

The participant is dismissed, and bumps into the lab assistant, who asks for help. DeSteno found those who had been helped by the assistant, and were grateful for it, were more likely to return the favour, and did so for longer than those in a group not helped.

"Gratitude leads people to act in virtuous or more selfless ways," said DeSteno, whose research was published earlier this year in the journal Current Directions in Psychological Science. "And it builds social support, which we know is tied to both physical and psychological well being."

Robert Emmons, a psychology professor at the University of California, Davis, said those who offer gratitude are less envious and resentful. They sleep longer, exercise more and report a drop in blood pressure, said Emmons, who wrote "Thanks! How Practicing Gratitude Can Make You Happier."

Brenda Shoshanna, a New York psychologist, agreed.

"You can't be depressed and grateful at the same time," said Shoshanna, the author of "365 Ways to Give Thanks: One for Every Day of the Year." "It makes a person physically, mentally, in every way healthier."

As for Golden, he doesn't pay much attention to the academics. He simply acknowledges he's "one lucky dude," grateful for his two children, two grandchildren, and his 89-year-old girlfriend.

When he celebrates U.S. Thanksgiving this Thursday, he and his family will gather around the table, hold hands and say thank you.

"It's surprising what those two little words do for a person," he said. "It's easy to say and it does a lot of good."