“Accumulating evidence indicates that living in greener areas is associated with many beneficial health outcomes,” wrote Bo-Yi Yang, Ph.D., of Sun Yat-sen University in Guangzhou, China, and colleagues. “Given that attention is a critical prerequisite for learning, greenness in school settings may be of great public health significance.”
The authors conducted the population-based study between April 2012 and January 2013 in seven northeastern China cities. The analysis included 59,754 children (aged 2 to 17 years) from 94 schools, including kindergartens. Students who had lived at their current address for two years or longer were eligible for the study.
Participants’ parents and guardians completed the ADHD DSM-IV survey, rating the frequency that each ADHD symptom had occurred in the preceding six months on a four-point scale ranging from “never or rare” to “very often.” Children exhibiting six or more symptoms of either inattention or hyperactivity-impulsivity were defined as having ADHD symptoms.
Green space around schools and kindergartens was assessed using the normalized difference vegetation index (NDVI) and the soil-adjusted vegetation index (SAVI). Values ranged from negative one to one, with higher values indicating more green space (such as leaves and grasses), negative value representing bodies of water, and values close to 0 generally indicating barren areas, such as rock. Greenness estimates were based on satellite images taken in August 2010, “the greenest month in northeastern China,” according to the study.
Of the participants, 4.3%, or 2,566 students, had ADHD symptoms. The researchers found that a 0.1 unit increase in the NDVI or SAVI within 500 meters of a school or kindergarten was significantly associated with lower odds of ADHD symptoms. Associations persisted when adjusting for age, sex, parental education level, parental income level, type of home district, and dog ownership.
The authors offered several potential explanations for their findings. One hypothesis is that humans are innately attracted to nature, and the natural world may be beneficial to brain development. Green space may also encourage physical exercise and reduce the level of air pollutants, they noted.
The authors concluded that their findings “are relevant to policymakers and health care authorities for translating evidence into feasible and achievable targeted interventions (for example, planning for green spaces around schools and kindergartens) to mitigate the burden of ADHD in children.”
For related information, see the Psychiatric News article “Lingering in a Garden,” by Ezra E. H. Griffith, M.D.