A generalized relationship between dose of greenness and mental health response

Abstract

Exposure to green spaces is a boon to urbanites. Over the last four decades, an increasing number of researchers have shown interest in exploring the relationship between the dose of greenness and mental health response. Early studies suggested a linear dose–response relationship, making it challenging to identify the most beneficial doses of greenness. However, findings from a rapidly growing body of recent research indicate the possible existence of a generalized curvilinear pattern. Despite this, these studies have used varying measures and contexts, resulting in inconclusive evidence. Without fully understanding the nature of the relationship, we do not know how to allocate green landscape resources to maximize mental health benefits. This study aimed to identify a generalized pattern to describe the dose–response relationship between urban greenness and mental health. Through a meta-analysis of all relevant studies, we found sufficient samples to generalize the dose–response curve for greenness intensity. Our analysis revealed that a quadratic pattern best fits most of the published greenness curves, and we identified the highly beneficial and best doses of eye-level greenness and top-down greenness. This study identifies and rationalizes a generalized quadratic pattern describing the dose of greenness–mental health response curves, addressing a critical knowledge gap across multiple fields. In practice, a moderate ‘dose’ of urban greenness exposure provides the most salubrious supply of mental health benefits. With nature in cities, as with the chemicals we ingest, the dose can make the difference. This analysis looks across other studies to find that, in practice, a moderate ‘dose’ of urban greenness provides the greatest mental health benefits.