Nice knee slapper best Rx for body, soul, study finds Whoever said laughter is the best medicine really knew what he was talking about. Laughter is good for the soul - and for the body.

Most of us have been laughing since we were babies. Spontaneous laughter is seen in infants as early as 5 weeks of age.By the age of 3, everything seems funny. The average child laughs some 300 times a day. But the realities of life bring out our serious sides, and by the time we're all grown up, we're laughing a measly 15 times a day.

There are all kinds of laughs - from harmonious tinkling to loud braying. Physiologically, the sound of laughter is produced in a similar manner to that of a hiccup or cough. A deep inhalation of air is followed by short, spasmodic contractions of the diaphragm. Whether you giggle or guffaw, the physiological mechanism of laughter is basically the same for everyone. The actual sound that you end up letting loose depends on the size and shape of your body, your emotional state and some hereditary factors.

Little is understood about the process of laughing, but we do know that about four-tenths of a second after we realize that something is funny, a negatively charged wave of electricity sweeps over the entire outer surface of the brain. Electrical impulses set off a chain of chemical reactions, and endorphins and enkephalines are released. These opiate-like substances are the body's natural tranquilizers and painkillers, and produce feelings of pleasure and occasionally even a "natural high."

The same process decreases the production of catecholamines, chemicals normally secreted during the fight or flight response that can weaken the body's defenses and slow healing.

Laughter gives a boost to the body's disease-fighting army, the immune system. A hearty laugh has been shown to activate cellular soldiers called T lymphocytes and natural killer cells. It increases the production of immunoglobulins to protect the body from viruses and other foreign invaders.

In his book, "Anatomy of an Illness," Norman Cousins proposed the use of laughter as a healing tool. Suffering from a rare form of painful arthritis, Cousins found traditional medicines ineffective and decided to cure himself with daily doses of humor. He found that when he watched Marx Brothers' films and episodes of Candid Camera, his gleeful laughter helped him sleep better and stay comfortable with fewer pain pills.

Cousins' groundbreaking work in 1979 led to more extensive research into the therapeutic benefits of laughter. Although clowns haven't totally replaced doctors, humor therapy has gained respectability, and children's wards and nursing homes routinely use laughter as a healing modality.

Laughing is good exercise. A hearty laugh is a good workout for the diaphragm, the lungs and the muscles of the abdomen, face and chest. Laughing increases the blood's oxygen level and gently tones the cardiovascular system. Circulation is improved, and stale air is blown out of the lungs. When the laughter subsides, heart rate and blood pressure drop below normal, leaving the laugher profoundly relaxed. This sense of relaxation lasts up to 45 minutes, and may be beneficial in countering heart disease, high blood pressure and depression.

Laughter is a natural coping mechanism - a healthy alternative to a stress-relieving cigarette or martini. Laughing leads to a cleansing release of emotion, and it's a socially acceptable way to vent pent-up frustration, blow off anger and shed tension. The state of relaxation that follows a good knee slapper re-energizes us and helps us find positive solutions to life's challenges.

If there were a pill that offered all the healthy benefits of laughter, most doctors would be prescribing it, and most of us would be taking it. But pills aren't necessary - laughter really is the best medicine.