About 2 h/week in nature seems a good target.
Study in 36 city dwellers: spending time in nature (a 'nature pill' of ~20-30 minutes) reduced salivary cortisol and alpha-amylase, stress markers, in their real daily lives. Supports contact with nature to lower stress.
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Regular contact with nature (parks, forests, green areas, natural spaces) has documented effects on mental, cardiovascular, immune, and cognitive health that research over the past two decades has begun to quantify rigorously; growing worldwide urbanization and the shift in lifestyle patterns toward predominantly artificial environments (indoors, digital devices) make "nature deficit" a new public health risk factor that deserves explicit clinical attention, especially because the interventions to correct it are simple, accessible, essentially free, and have an unbeatable tolerability profile.
The indication with the strongest clinical support is the modulation of chronic stress: multiple studies have documented significant reductions in salivary cortisol, heart rate, and autonomic markers of stress (heart rate variability) with exposure to natural environments for 20-30 minutes, compared with equivalent urban environments; the "minimum effective threshold" according to the study by White and colleagues published in 2019 in Scientific Reports with 20,000 participants is approximately 2 hours a week of contact with nature, with significant benefits in subjective well-being and self-reported health that continue up to about 5 hours a week and level off afterward.
"Attention restoration theory" proposes that natural environments contain gently engaging stimuli (rustling leaves, the sound of wind, running water) that allow the directed attention demanded by work and urban settings to "rest," restoring sustained attentional capacity; several experimental studies have documented significant improvements in attention and working memory tasks after walks in natural environments compared with urban walks equivalent in duration and physical intensity.
"Shinrin-yoku," or forest therapy, a traditional Japanese practice of immersion in forest environments that the Japanese government has incorporated into its public health recommendations, has a clinical basis in studies documenting significant increases in circulating NK (natural killer) cells and in antitumor immune activity after days of forest immersion; phytoncides (volatile antimicrobial compounds released by trees, especially conifers such as pines, firs, and cypresses) appear to mediate part of these immunomodulatory effects.
In prospective population studies, the availability and use of residential green spaces is associated with modest but significant reductions in cardiovascular and all-cause mortality, a robust association documented in European and North American cohorts; the proposed mechanisms include reduced chronic stress, increased physical activity, improved air quality, and modulation of systemic inflammatory markers.
In mild to moderate depression and anxiety disorders, several structured "ecotherapy" interventions (group walks, therapeutic gardening, supervised outdoor activities) have shown significant improvements on clinical scales comparable to some pharmacological interventions; epidemiological data associate the availability of green spaces with lower rates of depression and suicide in urban cohorts.
Based on the evidence, reasonable recommendations are: at least 2 hours a week of contact with nature (parks, forests, green spaces), preferably in sessions of 20-30 minutes or longer; prioritize natural spaces over urban spaces whenever possible; combine contact with nature with moderate physical activity (walking, gardening, outdoor sports) for additional synergy; in children, prescribing structured outdoor time has important effects on cognitive development, mental health, myopia, and body composition; in older adults, the accessibility of residential green spaces is one of the most important environmental factors for healthy aging.
Contact with nature has an exceptional safety profile, with no relevant specific contraindications; practical considerations include caution with excessive sun exposure (adequate protection), avoiding areas with a high incidence of ticks or dangerous animals depending on the region, attention to people with seasonal allergies or significant allergic asthma (which may limit exposure in specific seasons), and consideration of mobility and accessibility for people with physical limitations or older adults; home gardening, walks in accessible urban parks, weekend activities in natural settings, and short outdoor breaks during the workday are all strategies accessible to most urban people; deliberately integrating contact with nature into the weekly routine is probably one of the lifestyle interventions with the best cost-benefit ratio in terms of overall well-being, with no need for technology, supplements, or significant financial investment.
Information, not medical advice. Scientific evidence reflects the quality of the studies.