Filter Publications
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 moreDemographic and Geographical Determinants of Human Olfactory Perception of 909 Individuals Inhabiting 16 Regions
The hedonic perception of odors is similar worldwide. However, our perception of smells is much more than just determining whether an odor is pleasant or not. Here, we expanded this assessment by recruiting 909 people from 16 regions of the world and measuring 12 perceptual dimensions (e.g., pleasantness, intensity, edibility), which were aggregated into an olfactory perceptual fingerprint. We used two fingerprints: descriptor-specific and odor-specific. Age, gender, and region explained 1.1%, 0.3%, and 9.6% of variance in the descriptor-specific fingerprints, respectively. Similarly, age, gender, and region explained 0.5%, 0.3%, and 8.2% of variance in the odor-specific fingerprints. Interestingly, odor intensity was more regionally dependent than pleasantness. Thus, olfactory perception across the globe may be better differentiated by odor intensity than pleasantness. Although there is some influence of individual and cultural backgrounds, human perception of odors appears to be quite similar worldwide, even when assessed using 12 perceptual dimensions. Highlights Olfactory perception of 909 people from 16 regions was evaluated Human perception of odors appears to be quite similar worldwide Olfactory perception worldwide is better differentiated by intensity than hedonics Age and gender had a limited impact on individual perception of odors
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
Read moreNature and Human Well-Being: The Olfactory Pathway
Figure 1. Conceptual framework of the pathway from exposure to natural olfactory environments to human well-being. The olfactory environment is characterized by the concentrations and ratios of airborne chemicals. Dimensions of olfactory function (i.e., sensitivity, discrimination, and identification) are influenced by a variety of individual and environmental factors, which together moderate olfactory perception. Subjective experience is a mediator through which olfactory perceptions lead to well-being outcomes. Relevant determinants of this experience include individual preference, culture, association, prior experience, and multisensory context. Other pathways to well-being include those that occur below the threshold of perception (i.e., subthreshold) and those that occur via initial affective responses that are suprathreshold but independent of top-down processes related to subjective experience. These components lead to a variety of well-being outcomes, from broader dimensions such as quality of and satisfaction with life, to emotional responses and emotion regulation, cognitive function, influences on behavior (social interactions and dietary choices), stress, depressive symptoms, (anti-)inflammatory processes, and effects from exposures to pathogens. Together, these outcomes are the result of subthreshold biochemical processes, initial affective responses, and subjective appraisals of odors from nature. A variety of other pathways mediate the relationship between olfactory environments and human well-being, although they are not illustrated here. Credit: University of Washington The world is undergoing massive atmospheric and ecological change, driving unprecedented challenges to human well-being. Olfaction is a key sensory system through which these impacts occur. The sense of smell influences quality of and satisfaction with life, emotion, emotion regulation, cognitive function, social interactions, dietary choices, stress, and depressive symptoms. Exposures via the olfactory pathway can also lead to (anti-)inflammatory outcomes. Increased understanding is needed regarding the ways in which odorants generated by nature (i.e., natural olfactory environments) affect human well-being. With perspectives from a range of health, social, and natural sciences, we provide an overview of this unique sensory system, four consensus statements regarding olfaction and the environment, and a conceptual framework that integrates the olfactory pathway into an understanding of the effects of natural environments on human well-being. We then discuss how this framework can contribute to better accounting of the impacts of policy and land-use decision-making on natural olfactory environments and, in turn, on planetary health. Related Media How the smells of nature can affect human well-being (May 29, 2024) How do the smells of nature affect well-being? A call for more research. (May 23, 2024) Nature’s scents linked to improved health and well-being (May 16, 2024)
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