I am reading a book right now and they discussed how one city had an unusually higher number of people who had lived past 100 years. The researcher spent tons of money researching their diet and their lifestyle and their economic situation and their education and there genes to figure out this mysterious cause of long life and failed to pinpoint a medical reason for their long life, it was later concluded they lived longer because of the quality of their social relationships. As new people moved into the city and as old people died or moved out, their lifespan began to decline to reflect the surrounding cities next to them.
I believe that helping others makes us happy and hurting others makes us miserable, even if we do not realize it at the time, it might be a subconscious or even an unconscious thing, the bible says that respecting people is a part of fearing God and that fearing God, which involves respecting others lengthens our lives. For example, do you notice you have fewer health problems when you spend a day or weak helping others as opposed to when you spend a day or weak helping yourself? Kindness is medicine not only for your soul and your relationships but also for your body, and mind.