A recent study aimed to find out just that. The research only looked into the effectiveness of individual-level wellbeing responses (instead of organization-level responses), meaning interventions to change workers’ attitudes and behaviors through (for example) mindfulness, resilience training, and wellbeing apps. Organisational-level approaches, on the other hand, change how work is structured and aim to minimize sources of stress and insecurity.
The results surprisingly show that employees who were subjected to these individual wellbeing approaches were, on average, not better off than those without interventions. In other words, their mental wellbeing was not reliably better than those without wellbeing interventions. Resilience and stress management even seems to slightly decrease wellbeing. The reason for these results could be that these individual wellbeing interventions only target the symptoms of stress, but often forego the source, which could be entirely unrelated to work as well.
Interestingly however, one individual intervention did end up making a positive impact on wellbeing; volunteering. A possible explanation might be that research shows that trying to make others happy is a more effective way to become happy than trying to make yourself happy. Meaningful work (un)related to working activities might be a strong way to increase employee wellbeing (and make a positive impact in the process).