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Associations of Forest vs. Urban Environmental Exposure With Well-Being and Nasal Microbiome Composition: An Exploratory Pilot Study
Highlights An 8-week forest vs. urban exposure was associated with affective improvements. Greater post-exposure richness in forest vs. urban group’s nasal microbiomes. Forest group’s nasal microbiome enriched with well-being-associated bacteria. Increased nasal bacterial richness correlated with affective improvements. Bifidobacterium and Akkermansia abundance correlated with affective improvements. The benefits of nature exposure for human well-being are well-recognized, yet much remains to be understood about the underlying causal mechanisms. This exploratory, hypothesis-generating pilot study used a natural experimental design with University of Washington students (Seattle, WA, USA; 2024) to investigate links between the nasal microbiome and well-being over an 8-week forest vs. urban environment exposure. After an academic year (September-May) during which all participants (N = 13) were full-time students in Seattle, one group relocated to remote forest sites in western Washington (n = 5; forest condition), while another group remained in urban Seattle (n = 8; urban condition). Self-reported affect, rumination, and mental well-being were assessed pre- and post-exposure using validated surveys, and nasal swabs were collected pre- and post-exposure for nasal microbiome profiling via 16S rRNA gene sequencing. Compared to the urban group, the forest group exhibited significantly greater increases in positive affect and decreases in negative affect and rumination. While no between-group differences in overall nasal bacterial community composition were detected pre-exposure, significant differences emerged post-exposure. Moreover, the forest group exhibited greater post-exposure taxonomic richness at a marginally statistically significant level and significant enrichment of taxa previously associated with well-being (e.g., Bifidobacterium, Akkermansia), changes not observed in the urban group. Increases in taxonomic richness and the relative abundance of these key taxa were significantly associated with affective improvements. These preliminary results suggest that nasal microbiome-mediated pathways linking nature exposure with well-being merit further investigation.
Read moreCommunity Forests and Public Health: A Research Agenda
The natural environment is integral to supporting healthy and resilient communities. Community forests (CFs) are forested parcels, typically in rural areas, where community members have access, share governance, and receive various benefits. While considerable research demonstrates that urban parks and forests are important for human health, similar assessments are less available for CFs specifically. Although CFs exist in multiple countries, their policy, ecological, ownership, and governance contexts differ significantly. This review focuses on CFs in the United States. The goals of this project were to systematically review current evidence on the relationship between CFs and human health, identify knowledge gaps in the existing research, and propose a scientific research agenda that identifies critical questions related to CFs and public health in the U.S., with application in other contexts. We conducted a systematic review of the literature, screening 351 studies and assessing twenty-four full-text articles, only one of which met inclusion criteria. This mixed-methods study characterized 70 CFs in the Eastern U.S. and featured four case studies. The majority of CFs (93%) and all case studies identified recreational use as their most common purpose. The evidence base on the health implications of CFs is very thin. Targeted research on CFs and their impact on health could provide evidence to inform CF processes and help optimize their health outcomes. We propose a research agenda on CFs in the U.S. based on several pathways of public health promotion: nature contact, climate mitigation/adaptation, economic opportunities, community cohesion, and equity.
Read moreForest Terpenes and Stress: Examining the Associations of Filtered vs. Non-filtered Air in a Real-Life Natural Environment
Human health may benefit from exposure to a class of biogenic volatile organic compounds (BVOCs) consisting of isoprene units, known as terpenes. In this double-blind, randomized crossover trial, participants sat in a forest for two 60-min sessions, one in which terpenes were filtered out of the ambient air they breathed, and another in which they were not, separated by a minimum of an eight-day washout period. The primary outcome was the high frequency (HF) component of heart rate variability (HRV; measured continuously). Secondary outcomes included skin conductance levels (SCL) (measured continuously), self-reported stress and affect (measured every 20 min), blood pressure, heart rate, cortisol and inflammatory cytokines (measured before and after sessions). Serum concentrations of terpenes (measured before and after sessions) were also assessed to investigate the association of absorbed dose with these outcomes. We did not observe a significant association of filter condition with most outcomes; although the trends for affect, systolic blood pressure, cortisol, TNF-α, and CRP were all in the hypothesized direction. We did observe a significant association with interleukin-6, which was −0.19 pg/mL lower in the terpenes-on vs. terpenes-off condition, adjusted for baseline (95 % CI: −0.35, −0.03); and SCL over the session as a whole. A sensitivity analysis of the subset of data from participants who completed both conditions supports these findings and revealed additional significant associations with SCL (95 % CI: −1.87, −0.05); and TNF-α (95 % CI: −2.63, −0.10). To our knowledge, this is the first RCT to filter terpenes from ambient air during forest contact. Highlights Powered Air Purifying Respirator (PAPR) helmets filtered terpenes from forest air. Psychophysiological and immunological correlates of stress were assessed. IL-6 serum levels lower after sessions with terpenes-on vs. terpenes-off filter. Skin conductance levels (SCL) lower across time with terpenes-on vs. terpenes-off. All other outcomes not significant, but many trended in the hypothesized directions. Keywords Terpenes; Forest; Nature; Health; Stress
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