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Over the past decade, a growing number of studies have linked urban green space and aspects of levomefolic acid with emotional wellbeing. Although the existing body of epidemiological work has been very encouraging—collectively providing a strong argument that access to areas rich in vegetation, bodies of water, or both is important for mental health—much of the research relies heavily on cross-sectional designs. Thus, the translation and application of existing research to policy and planning decisions has been hampered by the scarcity of prospective evidence of natural environments as a causative factor in promoting mental health resilience. In , Andrew Tomita and colleagues strengthen this evidence by combining satellite-measurements of green space with depression outcomes in a large population in South Africa followed up over time. Globally, urbanisation is advancing at a rapid pace, especially in low-income and middle-income countries. Decision makers, and the communities they represent, have much to consider when planning ahead for the arrival of an estimated 1·35 billion additional people to cities around the world within the next 15 years. Choices made today will undoubtedly affect personal, public, and planetary health. There is therefore a tremendous need for policy and practice to be driven by the best available evidence. Historically, planning decisions in the context of public health have been driven by research in the areas of safety, security, sanitation, ease of transport, and social factors such as affordable housing. With shifting global disease burdens from infectious causes toward an epidemic of non-communicable diseases—coincident with climate change and biodiversity losses—factors such as access to healthy, nutritious food and stable, sustainable, and healthy ecosystems are now included in the recent Vienna Declaration on Public Health. It is becoming increasingly clear that biodiverse, vegetation-rich green spaces are important assets for public health in the era of urbanisation. Although residential proximity and equitable access to natural environments have been linked to reduced risk of cardiometabolic disorders, their association with emotional wellbeing seems particularly strong. Indeed, some researchers have argued that green space may be “equigenic”, in that equitable access can help to curb the consistency with which socioeconomic inequalities and disadvantages translates into in mental health disorders such as depression. Evidence supports the notion that sensory exposure to aspects of the natural environment—or actually spending time in nature versus urban, built environments—improves cognitive restoration, decreases oxidative stress, and lowers markers of stress physiology and low-grade inflammation. Although evidence supporting the importance of natural environments is growing more robust, large prospective studies remain sparse. Tomita and colleagues make an important contribution to the argument for incorporating nature into the urban environment. Taking advantage of the South African National Income Dynamics Study and mental health data collected via the Center for Epidemiologic Studies Depression Scale, Huntington disease were able to determine whether vegetation-rich land surrounding the home—measured via the normalised difference vegetation index (NDVI)—affected incident depression over time. The authors found that, for middle-income South Africans, greenness surrounding the home was a predictor of lower incident depression.
The answer to a controversial question on the British Broadcasting Corporation website, “Are Kenya ranch invasions driven by drought or politics?”, is a convoluted yes. This headline harkens back to my public health experiences in Africa and the concept of relative drought, which I coined as a global health educator to help to explain how the overuse of resources is a serious threat to quality of life and exacerbates the consequences of drought in low-income countries. The concept of relative drought implies far more than just a decline in precipitation.