Kindness and longevity appear connected in research on ageing and social behaviour, with people who volunteer or help others regularly tending to show better health outcomes over time than otherwise similar people who do not, an effect that holds up even after accounting for existing differences in health and circumstance.
Part of the explanation seems to run through social connection: helping others usually involves some form of contact with people, and strong social ties are themselves one of the more consistent predictors of a longer, healthier life, which suggests kindness may work partly by simply keeping a person meaningfully connected.
None of this means kindness functions as a medical treatment, but it does suggest that a habit often framed purely as a moral virtue also carries a quiet, measurable practical benefit for the person practising it, alongside whatever benefit it clearly provides to the person receiving it. That patience, more than anything else, tends to separate the approaches that actually hold up.