Filter Publications
Forest 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
Read moreSusceptibility to Stress and Nature Exposure: Unveiling Differential Susceptibility to Physical Environments; A Randomized Controlled Trial
Figure 1. Theoretical framework. Emerging epidemiological evidence indicates that nature exposure could be associated with cardiovascular health among individuals in low socioeconomic positions to a greater degree than among more privileged groups. Continue reading at PLOS ONE. Background Emerging epidemiological evidence indicates nature exposure could be associated with greater health benefits among groups in lower versus higher socioeconomic positions. One possible mechanism underpinning this evidence is described by our framework: (susceptibility) adults in low socioeconomic positions face higher exposure to persistent psychosocial stressors in early life, inducing a pro-inflammatory phenotype as a lifelong susceptibility to stress; (differential susceptibility) susceptible adults are more sensitive to the health risks of adverse (stress-promoting) environments, but also to the health benefits of protective (stress-buffering) environments. Objective Experimental investigation of a pro-inflammatory phenotype as a mechanism facilitating greater stress recovery from nature exposure. Methods We determined differences in stress recovery (via heart rate variability) caused by exposure to a nature or office virtual reality environment (10 min) after an acute stressor among 64 healthy college-age males with varying levels of susceptibility (socioeconomic status, early life stress, and a pro-inflammatory state [inflammatory reactivity and glucocorticoid resistance to an in vitro bacterial challenge]). Results Findings for inflammatory reactivity and glucocorticoid resistance were modest but consistently trended towards better recovery in the nature condition. Differences in recovery were not observed for socioeconomic status or early life stress. Discussion Among healthy college-age males, we observed expected trends according to their differential susceptibility when assessed as inflammatory reactivity and glucocorticoid resistance, suggesting these biological correlates of susceptibility could be more proximal indicators than self-reported assessments of socioeconomic status and early life stress. If future research in more diverse populations aligns with these trends, this could support an alternative conceptualization of susceptibility as increased environmental sensitivity, reflecting heightened responses to adverse, but also protective environments. With this knowledge, future investigators could examine how individual differences in environmental sensitivity could provide an opportunity for those who are the most susceptible to experience the greatest health benefits from nature exposure.
Read moreMore Green, Less Lonely? A Longitudinal Cohort Study
Figure 1. Association between green space within 1600 m and cumulative incidence of loneliness in all participants, and among those living alone at baseline and follow-up Both models were fully adjusted, including age group, sex, children, cohabitation status, percentage green space within 1600 m, highest educational qualifications, annual household income, % of last 12 months spent unemployed, disability or limiting long-term health condition, area-level socio-economic circumstances. Background Urban greening may reduce loneliness by offering opportunities for solace, social reconnection and supporting processes such as stress relief. We (i) assessed associations between residential green space and cumulative incidence of, and relief from, loneliness over 4 years; and (ii) explored contingencies by age, sex, disability and cohabitation status. Methods Multilevel logistic regressions of change in loneliness status in 8049 city-dwellers between 2013 (baseline) and 2017 (follow-up) in the Household, Income and Labour Dynamics in Australia study. Associations with objectively measured discrete green-space buffers (e.g. parks) (<400, <800 and <1600 m) were adjusted for age, sex, disability, cohabitation status, children and socio-economic variables. Results were translated into absolute risk reductions in loneliness per 10% increase in urban greening. Results The absolute risk of loneliness rose from 15.9% to 16.9% over the 4 years; however, a 10% increase in urban greening within 1.6 km was associated with lower cumulative incident loneliness [odds ratio (OR) = 0.927, 95% confidence interval (CI) = 0.862 to 0.996; absolute risk reduction = 0.66%]. Stronger association was observed for people living alone (OR = 0.828, 95% CI = 0.725 to 0.944). In comparison to people with <10% green space, the ORs for cumulative incident loneliness were 0.833 (95% CI = 0.695 to 0.997), 0.790 (95% CI = 0.624 to 1.000) and 0.736 (95% CI = 0.549 to 0.986) for 10–20%, 20–30% and >30% green space, respectively. Compared with the <10% green-space reference group with 13.78% incident loneliness over 4 years and conservatively assuming no impact on incident loneliness, associations translated into absolute risk reductions of 1.70%, 2.26% and 2.72% within populations with 10–20%, 20–30% and >30% green space, respectively. These associations were stronger again for people living alone, with 10–20% (OR = 0.608, 95% CI = 0.448 to 0.826), 20–30% (OR = 0.649, 95% CI = 0.436 to 0.966) and >30% (OR = 0.480, 95% CI = 0.278 to 0.829) green space within 1600 m. No age, sex or disability-related contingencies, associations with green space within 400 or 800 m or relief from loneliness reported at baseline were observed. Conclusions A lower cumulative incidence of loneliness was observed among people with more green space within 1600 m of home, especially for people living alone. Potential biopsychosocial mechanisms warrant investigation.
Read moreNature and Health: Perspectives and Pathways
As many scholars have noted, research and publications on the benefits of nature experience have grown substantially over recent years. Progress has been made on empirical fronts based on perspectives from psychology, epidemiology, sociology, exposure science, urban design, and other disciplines. Studies have revealed ways in which health outcomes differ by population characteristics (e.g., socioeconomic status), individual differences (e.g., states of baseline mental health), and interactions with different types of nature (e.g., street trees vs. large parks vs. deserts) (Barnes et al., 2019; Mitchell & Popham, 2008; Mitchell, Richardson, & Shortt, 2015; Olvera-Alvarez, Browning, Neophytou, & Bratman, 2021; Tester-Jones et al., 2020; Wheeler et al., 2015; Yin, Bratman, Browning, Spengler, & Olvera-Alvarez, 2022). Together, the evidence also illustrates the importance of accounting for different ways of “operationalizing nature” (e.g., Normalized Difference Vegetation Index [NDVI]), and methods of measuring exposure (e.g., subjective vs. objective), as well as the granularity in assessments of frequency and duration (Ekkel & de Vries, 2017; Shanahan et al., 2016).
Read moreLiving in Cities, Naturally
Figure 1. Together with ecological benefits such as climate change mitigation and the protection of biological diversity, the renaturing of cities opens opportunities for people to engage with features and processes of the natural world; for example, when tending plants in a community garden. Natural features, settings, and processes in urban areas can help to reduce stress associated with urban life. In this and other ways, public health benefits from, street trees, green roofs, community gardens, parks and open spaces, and extensive connective pathways for walking and biking. Such urban design provisions can also yield ecological benefits, not only directly but also through the role they play in shaping attitudes toward the environment and environmental protection. Knowledge of the psychological benefits of nature experience supports efforts to better integrate nature into the architecture, infrastructure, and public spaces of urban areas.
Read moreNature and Health
Figure 1: Some pathways through which the natural environment can affect the health of broad segments of populations. Urbanization, resource exploitation, and lifestyle changes have diminished possibilities for human contact with nature in many societies. Concern about the loss has helped motivate research on the health benefits of contact with nature. Reviewing that research here, we focus on nature as represented by aspects of the physical environment relevant to planning, design, and policy measures that serve broad segments of urbanized societies. We discuss difficulties in defining “nature” and reasons for the current expansion of the research field, and we assess available reviews. We then consider research on pathways between nature and health involving air quality, physical activity, social cohesion, and stress reduction. Finally, we discuss methodological issues and priorities for future research. The extant research does describe an array of benefits of contact with nature, and evidence regarding some benefits is strong; however, some findings indicate caution is needed in applying beliefs about those benefits, and substantial gaps in knowledge remain.
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