They say laughing is the best medicine, how truth it is?

It's true that laughing is the best medicine. If you have a happy mood all the time, the disease will keep away from you. Sometimes a good mood is even better than the medicine. I love China

For me, this is more to psychological side. We laugh because we are happy. When happy, we are free from any stress or tiredness. When we are not stress, our brain can work normally. When our brain like that, our body system like heart and etc will in the calm situation. So, all the system will work normally . Haha, I'm not a doctor nor the medical practitioner, so this is just my own theory ; )