Here is the beginning of the article I wrote for Woman’s Day, 1 April 1999 (was it a coincidence that they ran it on April Fool’s Day?)

SMILE!
Being happy is good for your health. Really
By Robin Marantz Henig

Donna Regan had just slogged through a particularly lousy week. Work had gone badly. Her husband was out of town. She was premenstrual, something that always made her feel crabby and blue. And now she had to drag herself out of the house on Saturday morning to go to her daughter’s soccer game.

But once at the field, a little magic happened. Donna became so absorbed in the action that she found herself cheering and yelling. She cheered even more when her daughter scored a goal. By the time the referee blew the final whistle, she felt positively happy.

Happiness. Too bad we can’t bottle it. In fact, Donna may have recharged more than just her mental outlook that morning. Experts now say that laughter lowers stress hormones and boosts the immune system. Optimists live longer than pessimists. Happy people have more friends, and friendships help shield us from the ravages of disease.

"We’ve always heard that laughter is good for you," says Lee S. Berk, D.P.H., at the Center of Neuroimmunology School of Medicine at Loma Linda University in California. "Now we’re gathering the hard, serious medical evidence to show why this is so."

To boost your happiness and your health, try these tips culled from years of psychological and neurological research.

Put on a happy face. People who smile, even when they don’t feel especially happy, can make part of the "happy zone" in the brain’s left hemisphere surge with electrical activity. "Voluntarily producing smiles moves brain activity in the direction of spontaneous happiness," says Richard Davidson, Ph.D., professor of psychology and psychiatry at the University of Wisconsin in Madison.

In one of his numerous studies, subjects were hooked up to EEG machines, which measure brain wave activity, and shown funny movies. Smiling made their happy zones click wildly.

Unfortunately, this may not work for everyone, notes James Laird, Ph.D., professor of psychology at Clark University in Worcester, Massachusetts. He’s tested hundreds of people by having them alternate between happy and sad expressions. Happy faces usually brought on happy feelings. But some people got their emotional cues from outside influences rather than from their body’s messages. . . .

Box: Some Chuckle Statistics

An adult laughs an average of 15 times a day; a preschooler laughs an average of 400 times.

The happiest people, notes psychologist David G. Myers, author of The Pursuit of Happiness, share four traits: high self-esteem, a sense of personal control, optimism and an extroverted nature.

Just 100 laughs will boost your heart rate – and give you an aerobic workout – equal to that of a 10-minute session on a rowing machine, says William F. Fry, a professor emeritus at Stanford University School of Medicine, who performed the calculations on himself.