While we don't know all of the specifics, our immune system appears to benefit from these emotions. As a physician, it is often easy to prescribe medications to patients for a whole variety of maladies. One must be very cautious with the use of medications, especially in older adults. Many of my patients suffer significant pain from arthritis. Some of the theories regarding how one experiences pain suggest that a person can be distracted from pain by other sensations or feelings.
Laughter can actually distract from pain.
It is also a fallacy to think that humor declines with age. The benefits of humor take on a variety of forms in the physician's office. I hear many excellent jokes from my patients, and they take the form of all types of humor. This humor can actually be quite beneficial to the doctor-patient relationship. It is important for patients to be able to communicate with their physicians.