Here's what we know:
* Ancient Origins: The idea that laughter has healing power was present in ancient cultures. For example, the Greek philosopher Democritus, known as the "Laughing Philosopher," believed laughter was essential for good health.
* Early Literature: The phrase itself, or variations of it, appeared in early literature. For instance, William Shakespeare used the phrase "laugh and grow fat" in his play "The Merry Wives of Windsor," which implies a similar sentiment.
* Modern Usage: The phrase gained popularity in the 19th century, particularly in the works of humorists like Mark Twain and Charles Dickens. It became a common adage used to promote the benefits of humor and laughter.
So, while the exact origin is unclear, the idea that laughter is good for our health has been around for a long time, and the saying has evolved through various cultural and historical influences.