People who help others are helping themselves, new research published by the American Psychological Association suggests.
The study was led by Bryant PH Hui, at the University of Hong Kong, and a team of researchers who analyzed 201 independent studies looking at the link between kindness and wellbeing, and comprising 198,213 participants.
Although they found only a "modest" link between the two, with a "small effect size", they concluded that this was still meaningful given the number of people who perform acts of kindness every day.
"More than a quarter of Americans volunteer, for example," he said in the study, published in the Psychological Bulletin journal.
"A modest effect size can still have a significant impact at a societal level when many people are participating in the behavior."
The team also found variations in the degree to which good-hearted behaviour impacts the giver, with the type of kindness, and the giver's age, gender and demographics among the factors.
They found that random acts of kindness, like helping an elderly neighbour with their groceries, had a greater impact on overall wellbeing than formal behaviour, like scheduled volunteering for a charity.
Hui speculated that this may be due to the spontaneous nature of random acts of kindness, allowing more variety and warding off a sense of staleness or monotony.
Women were also more likely than men to experience feelings of wellbeing, with this possibly being down to meeting social expectations about being caregivers, Hui said.
The study distinguished between wellbeing linked to self-actualisation and finding meaning in life, and wellbeing as it relates to feelings of happiness and positivity.
Younger respondents were more likely to experience feelings of self-actualisation than older cohorts, who reported higher levels of physical health.
"Prosocial behaviour—altruism, cooperation, trust and compassion—are all necessary ingredients of a harmonious and well-functioning society," Hui said.
"It is part of the shared culture of humankind, and our analysis shows that it also contributes to mental and physical health."