any studies showing how social justice activism esp, or just activism and volunteerism, improve scores of mental health such as depression anxiety etc compared to general population or people who don't do activism/mental health.
Several studies have focused on whether involvement in volunteer activities or "civil society groups" (activist organisations, trade unions, block associations - any voluntary group) has a positive impact on mental health. Generally, the positive impact of volunteerism seem most marked for older Americans, since it helps them find a role for themselves. Involvement in civil society groups has been shown to be of mixed benefit, depending upon demographic variables.
A search on pubmed (www.pubmed.gov) for the terms activism and "mental health" retreived this citation:
Terry A. Kupers, "Psychotherapy, neutrality, and the role of activism," Community Mental Health Journal, Volume 29, Issue 6, Dec 1993, Pages 523 - 533, DOI 10.1007/BF00754261, URL http://dx.doi.org/10.1007/BF00754261
a similar search on the terms volunteering and "mental health" retrieved this link to an article:
http://jech.bmjjournals.com/cgi/content/full/58/6/493
and this article, for which a citation and abstract can be viewed by going to:
http://dx.doi.org/10.1016/S0277-9536(02)00025-4
Also, see:
J Health Soc Behav. 2001 Jun;42(2):115-31.
Volunteer work and well-being.
Thoits PA, Hewitt LN.
Department of Sociology, Box 1811-B, Vanderbilt University, Nashville, TN 37235, USA. peggy.thoits@vanderbilt.edu
Using two waves of panel data from Americans' Changing Lives (House 1995) (N = 2,681), we examine the relationships between volunteer work in the community and six aspects of personal well-being: happiness, life satisfaction, self-esteem, sense of control over life, physical health, and depression. Prior research has more often examined the effects of voluntary memberships than of volunteer work, has used cross-sectional rather than longitudinal data, and, when longitudinal, has emphasized social causation over selection effects. Focusing only on the consequences of volunteer work overlooks the antecedents of human agency. People with greater personality resources and better physical and mental health should be more likely to seek (or to be sought for) community service. Hence, we examine both selection and social causation effects. Results show that volunteer work indeed enhances all six aspects of well-being and, conversely, people who have greater well-being invest more hours in volunteer service. Given this, further understanding of self- versus social-selection processes seems an important next step. Do positive, healthy people actively seek out volunteer opportunities, or do organizations actively recruit individuals of these types (or both)? Explaining how positive consequences flow from volunteer service may offer a useful counterpoint to stress theory, which has focused primarily on negative life experiences and their sequelae.
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This answer to your question seems a little complicated. I did not find a study in pubmed.gov or OVID that linked the terms "activism" and "mental health" and gave results for a human study focused on answering your specific question. There is a body of work that examines the benefits of belonging to any voluntary association. As I said in my post the results have shown variations in benefit, depending upon such things a socio-economic status, age, etc.