The results of Study 2 provide the first experimental evidence to our knowledge that engaging in the prosocial act of writing gratitude notes enhances meaning in life. Participants assigned to write short notes of gratitude [(5–10 min writing short notes of gratitude to (up to) four people who have positively influenced their lives)] reported [5%] greater meaning in life (while statistically controlling for baseline levels of meaning) after expressing this prosocial behavior than participants in a neutral priming condition and marginally more than participants in the self-affirmation condition. Conversely, the self-affirmation prime did not increase meaning in life relative to the neutral condition. This provides additional evidence for the meaning provision hypothesis: prosocial actions are a source of meaning in life, and the results are not simply due to prosocial behaviors being self-affirming or solely a function of positive mood. […]
[W]e suspect that acting antisocially does not necessarily translate to lower meaning in life. Individual perceptions of meaning in life are necessarily subjective, and individuals derive meaning from various sources in life (see Heine et al., 2006; Wong, 1998). The results here suggest that prosocial behavior is one potential source of meaning. […] We further emphasize that prosocial behavior is but one way to procure meaning in life. There are other ways in which individuals can find meaning (e.g. having a successful career, cultivating a garden) that are not directly relevant to prosociality.
Prosociality enhances meaning in life, Tongeren et al, The Journal of Positive Psychology, 2016, https://dx.doi.org/10.1080/17439760.2015.1048814