Don't worry, be healthy

"A joyful heart is the health of the body, but a depressed spirit dries up the bones."

Who knew that the Old Testament sages who wrote the Book of Proverbs were medical researchers in disguise? It seems that laughter really is the best medicine.

Roughly every day, another study is released trumpeting yet another of the health benefits of happiness: Watching funny movies or listening to enjoyable music is good for our hearts. Those who are chipper and upbeat are less likely to catch colds, even after they're exposed to a virus. And cheerful people have significantly lower levels of a hormone that's been linked to Type 2 diabetes.

"If you go to a bookstore, you'll find a million books on happiness," says Michael Miller, director of the Center for Protective Cardiology at the University of Maryland Medical Center. "This is an area that's drawing a lot of interest from researchers and the public. Wouldn't it be great if there was something economical you could do to improve your health? It doesn't cost a lot to laugh and release endorphins that might be good for you."

True enough — and yet, that avalanche of studies, each one saying something slightly different or even downright contradictory, can be more bewildering than enlightening, more anxiety-producing than reassuring.

Scientists have been looking into the mind-body connection for a long time, but they focused mostly on the harmful effects of stress. It has only been in the past 10 years that they have begun to explore how positive emotions affect our health.

Happiness studies

Carol Graham, a senior fellow at the Brookings Institution in Washington, ranked a group of test subjects in 1995 on whether they were naturally jovial or gloomy, and then followed up with them five years later. She found that those with sunny dispositions were neither more nor less likely to get married, get divorced or suffer a job loss than the more downcast test subjects. But they were significantly healthier.

"Causality seems to run in both directions," says Graham, author of a book called "Happiness Around the World: The Paradox of Happy Peasants and Miserable Millionaires," which was published this month by Oxford University Press.

"Good health is linked to higher happiness levels, and health shocks — such as serious diseases or permanent disabilities — have negative and often lasting effects on happiness. At the same time, a number of studies find that happier people are healthier."

Miller, for instance, is the author of a 2005 study that established a connection between healthy hearts and laughter. About 20 volunteers were shown different movies. One group watched "Saving Private Ryan," Steven Spielberg's grim and graphic film about World War II while they were hooked up to a machine that measured the width of their veins. The other group was shown "Saturday Night Live" or a film comedy such as "There's Something About Mary."

The scientists found that the veins of volunteers who saw the depressing movie constricted, resulting in a higher blood pressure. In contrast, the veins of test subjects who watched the comedies widened, lessening the stress on their hearts.

Laugh it up

When people laugh, their brains release endorphins, a compound that suppresses pain. Endorphins have been demonstrated to activate receptors in the blood vessels. Miller's team is hypothesizing that these receptors in turn release a chemical called nitric oxide

"Nitric oxide is one of our most important heart-protecting chemicals," Miller says. "It does a whole host of great things, from relaxing blood vessels to reducing both inflammation and hardening of the arteries."

Note that Miller isn't sure that endorphins are instigating the release of nitric oxide; he's merely making an educated guess. While science is getting better at establishing that positive emotions really do benefit health, what isn't so clear is precisely how that process works.

"The mind-body connection represents the big black box in medicine," Miller says, "and we're just beginning to delve into it."

He and the other researchers caution that a fit of the giggles is no miracle cure. Positive emotions might be at their most effective at fighting stress-related illnesses in which the environment plays a role, such as heart ailments. Mirth might strengthen the immune system, helping it fight off viruses and other attacks from the outside.

But no amount of hilarity is likely to deter diseases that are largely inherited, such as sickle-cell anemia or some forms of cancer.

"It's unlikely that laughter will cure cancer, but it's also unlikely that it will cure heart disease," Miller says.

"Laughter may play a role in combating stress, but whether it also provides a bonus in addition to that is unknown. At the bare-bones minimum, laughter might offset some of the devastating effects of chronic disease. At most, it might help reduce the speed at which some diseases progress."

So it's conceivable that in the future, doctors might slightly change the advice they provide their healthy patients: Eat five servings of fruit and vegetables a day. Exercise and get plenty of rest. Read five jokes before bedtime.

"You know what they say about doctors," Miller says. "We practice medicine, but we never get it right. Maybe that's because we spend all our time battling disease instead of preventing it."