Exposure to Greener Environment at School Lowers Risk for ADHD in Children

A study published in JAMA Open Network found that greater levels of greenness in the school environment may be associated with significantly lower odds of attention deficit/hyperactivity disorder (ADHD) in school children.

Bo-Yi Yang, PhD, of Sun Yat-sen University, Guangzhou, China, and colleagues used Landsat satellite images to determine greenness surrounding 94 schools in 7 cities in Northeastern China and measured ADHD symptoms with the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). The parents of participants completed surveys with 4-point scales assessing 18 inattention and hyperactivity-impulsivity symptoms, as well as the 10-item Conners Abbreviated Symptom Questionnaire.

Levels of greenness were determined via the normalized difference and soil-adjusted vegetation indices. The study was completed between April 2012 and January 2013.

Of the 59,754 children (mean age, 10.3±3.6 years; 49.4% girls) in the study, 2566 (4.3%) had symptoms of ADHD. Children with ADHD were more likely to be boys (64.2% vs 50.0%), born to parents with lower education (38.4% vs 26.2%) or lower income (66.5% vs 57.6%), have 1 or more siblings (17.7% vs 15.3%), be born preterm (7.3% vs 5.3%), be born to a parent who smoked cigarettes (1.5% vs 0.6%) or drank alcohol (1.7% vs. 0.7%), and live in industrial or business areas (14.0% vs 12.2%). The investigators found no significant difference for breastfeeding or low birth weight.

Greenness levels differed considerably across schools, with the normalized difference vegetation index within 500 m (NVDI_500m) of the school ranging from −0.09 to 0.77. 

In unadjusted models, higher greenness exposure significantly lowered the odds of ADHD symptoms, with greater NVDI_500m and soil-adjusted vegetation index within 500 m (SAVI_500m) with odds ratios of 0.81 and 0.72, respectively. Repeated analysis using NVDI and SAVI at distances of 100 m and 1000 m demonstrated similar associations. The results remained consistent after adjusting for age, sex, parental education, family income level, type of home district, and dog ownership. Furthermore, the odds of having ADHD were lower for children ages 7 to 17 years vs children ages 2 to 6 years and children living in residential vs business or industrial areas.

The study was limited by China’s school policy restricting students to local schools, usually within 1 km of home, which may have had the effect of confounding greenness in the home environment with that of school. Furthermore the study design did not allow for examination of the timing between exposure to greenness and ADHD symptoms, and the use of satellite photos did not allow for examination of the quality of the vegetation.

In an accompanying article, Argelinda Baroni, MD, and Francisco Xavier Castellanos, MD, both of the department of child and adolescent psychiatry, Hassenfeld Children’s Hospital at New York University Langone, New York City, New York, noted that the importance of this study in “breaking new ground in extending the association between greenness and ADHD symptoms to non-Western populations,” as well as establishing the importance of exposure to nature on healthy neuronal development.

The investigators wrote, “The biophilia hypothesis suggests that human beings are innately attracted to nature, and, thus, contact with the natural world is postulated to be beneficial for children’s brain development and attention restoration.”

References

1. Yang B-Y, Zeng X-W, Markevych I, et al. Association between greenness surrounding schools and kindergartens and attention-deficit/ hyperactivity disorder in children in China. JAMA Network Open. 2019;2(12):e1917862.

2. Baroni A, Castellanos FX. Emerging insights into the association between nature exposure and healthy neuronal development. JAMA Network Open. 2019;2(12):e1917880.