"The positive effect of kindness on the immune system and on the increased production of serotonin in the brain has been proved on research studies. Serotonin is a naturally occurring substance in the body that makes us feel more comfortable, peaceful, and even blissful. In fact the role of most anti-depressants is to stimulate the serotonin production to alleviate depression. Research has shown that a simple act of kindness directed toward another improves the functioning of the immune system and stimulates production of serotonin in both the recipient of the kindness and the person extending the kindness.
Even more amazing is that persons observing the act of kindness have similar beneficial results. Imagine this: kindness extended, received, or observed beneficially impacts the physical health and feelings of everyone involved.