Smiling is a symptom of happiness that keeps you healthy.

RODALE NEWS, LENOX, MA—Who wants to live a long, healthy life?

When I ask people at my lectures that question, virtually every hand in the room shoots right up. When I ask who is willing to eat a low-fat, low-calorie diet, limit alcohol consumption, and exercise an hour a day, many of those eager hands go down. Then, just when they think the disciplined price of longevity may be too high, I tell them there’s a simple, painless way to add years to their life: smile. People who smile, sincerely and often, live longer. In fact, research published last month revealed that the intensity of an individual’s smile is a very good predictor of longevity.

THE DETAILS: A study in the journal Psychological Science looked at the intensity of the smiles of 230 major league baseball players whose photos appeared in the Sporting News Baseball Register in 1952. The researchers found that those players who flashed a broad, sincere smile lived longer than their fellow athletes who flashed a half-smile or no smile at all. Those who did not smile at all lived an average of 72.9 years. Those who cracked a half smile lived to 75, and those with a full, ear-to-ear grin lived an average of 79.9 years. Not smiling is almost as great a health risk as smoking!

To be fair, I need to state that forcing yourself to smile in the hopes of becoming an octogenarian is just not going work. The act of smiling is not what keeps you healthy. For the baseball players, the smile was simply an outward expression of their inner tendency toward happiness. Being happy is what keeps you healthy. A rapidly growing body of research demonstrates that positive emotions help us to stay healthy. Happy people tend to have stronger immune systems and healthier hearts than their less-enthusiastic counterparts. They get fewer infections and chronic illnesses, and have lower medical costs. And not surprisingly, happy people—the ones who flash a broad, heartfelt grin—tend to have enduring, stable marriages.

A study published last year looked at the smiles of men and women whose photos appeared in a high-school year book years earlier. Those who flashed a broad, sincere smile for their yearbook photo turned out to be much more likely to remain happily married than their non-smiling classmates.

WHAT IT MEANS: Before you run to the basement to check your high-school year book, and your spouse’s, consider this. It’s not the smile that helps you live longer or stay married. It’s the happiness, and the behaviors that accompany happiness. It may be too late to Photoshop a smile into your yearbook photo, but it’s not too late to change your future. Even though we’re born with our unique, innate and immutable temperament, it’s estimated that about 40 percent of our happiness is under our control. The lifestyle choices you make, and the way you think about yourself, largely determine how happy you will be. Abraham Lincoln got it right: “Most folks are about as happy as they make up their minds to be.”