Forest Exposure and Respiratory Function: A Literature Review

Environmental health research has recently started to study the health effects of well-being-promoting practices based on forest exposure. This narrative review aims to understand whether forest exposure can directly improve respiratory function. PubMed, Cochrane Library and Google Scholar were screened, up until April 2021, for clinical studies about changes of respiratory function induced by forest exposure, preferably measured with spirometry. Relevant evidence was summarized and critically discussed. Five studies were included in this review (three trials, an observational study and a case report). Globally, forest exposure seems to be associated with improved forced expiratory volume (FEV), peak expiratory flow (PEF) and forced vital capacity (FVC). In most included studies, exposure time was at least 1 h, and sessions were repeated over time. Study participants were either healthy subjects or patients with respiratory diseases. The benefits were reported, even in terms of inflammatory markers, and were detected in children, adults and elderly individuals of both genders. The number of participants per study ranged from 1 to 65. Forest exposure coupled with light physical activity may result in short-term improvements of some respiratory function parameters (FEV1, FEV6, PEF, FVC). Autonomic responses to environmental stimuli and the inhalation of some volatile compounds detectable in the forest air seem to directly contribute to the overall effect, which may be enhanced around waterfalls and creeks due to water nebulization. However, current scientific evidence is limited, and high atmospheric levels of some plant-derived compounds, especially when reacting with air pollutants, may even worsen certain respiratory conditions. Further studies on the topic are recommended to better quantify the effect size of forest-based interventions, assess long-term benefits, ascertain potential health risks and identify any moderator variables or confounding factors.