The biological effects of “green-therapy” on depressed patients

Major depressive and bipolar disorders are prevalent mental health conditions sharing the presence of major depressive episodes (MDEs). While psychopharmacological and psychological therapies are first-line treatments for MDEs, the response is often incomplete. New approaches focused on the human-nature relationship might complement antidepressant treatments, improving response. This PhD thesis aims to assess the feasibility of implementing regular exposure to green environments such as woods, forests, large parks, and gardens for at least forty-five minutes twice a week in a sample of patients experiencing a MDE and needing a modification of the antidepressant therapy. It also has the purpose of detecting changes in symptoms and neurocognitive, inflammatory and epigenetic biomarkers at two follow-up assessments: after six-week and after eight-month. Fifty-three patients were evaluated at the baseline; thirty-one completed the study. Nineteen (61%) of the completers reported regular exposure to greenery during the first follow-up, eleven (35%) during the second one. At six-week follow-up, actively exposed patients showed improvements in depressive symptoms, lower serum levels of C-reactive protein and interleukin-6, and higher adiponectin serum concentrations and acetylation level of H3K9 in peripheral blood mononuclear cells (PBMCs). At eight-months follow-up, instead, they showed amelioration in the speed of processing and an increase in the tri-methylation level of H3K9 in PBMCs. These results suggest that incorporating green exposure into clinical practice is feasible and potentially useful. However, more rigorous evaluations on larger samples are needed to verify whether exposure to greenery may complement MDEs treatment and favourably impact MDE-associated neurocognitive, inflammatory and epigenetic processes