In the Neighborhood: Connecting Plant Biomass and Childhood Obesity

May 14, 2005

"Time spent outdoors is the strongest predictor of activity in children," said Gilbert Liu, MD, at an epidemiology platform session here today &#8212 noting, at the same time, the reported dramatic drop in such activity among children. But as parks and green space increase in a given community, Dr. Liu pointed out, people walk more, more social cohesion develops, and the crime rate drops.

"Time spent outdoors is the strongest predictor of activity in children," said Gilbert Liu, MD, at an epidemiology platform session here today - noting, at the same time, the reported dramatic drop in such activity among children. But as parks and green space increase in a given community, Dr. Liu pointed out, people walk more, more social cohesion develops, and the crime rate drops.

The objective of the study conducted by Dr. Liu and his colleagues - Neighborhood Plant Biomass and Childhood Overweight - was, he noted, "to examine relationships between the normalized difference vegetation index, or NDVI," an indicator of green space, "and body mass index in urban and suburban children."

The study used satellite imagery and spatial analysis geographic information systems (GIS) to look at areas of 0.5 km, 1 km, and 1.5 km surrounding each of the 8,267 subjects, known as buffer zones, that are based on an understanding of how far people tend to walk and how people perceive their neighborhood.

The results showed that, with a prevalence of childhood overweight of 21.5% among the population studied, there was "a significant inverse relationship between BMI z-scores and NDVI for all three buffer sizes." It was also found that, "as plant biomass of a region declined, BMI values grew further from the mean." (In a logistic regression, however, NDVI was not significantly associated with childhood overweight.)

Liu concluded that "increased study of the influence of urban form on health is needed. NDVI may provide valuable information to planners and public health providers regarding the extent that neighborhoods promote or impede physical activity, and, ultimately, obesity." He also commented that GIS are a valuable tool for urban planning approaches for "protecting our kids from being overweight."