By Janice F. Bell, Jeffrey S. Wilson, and Gilbert C. Liu
Indianapolis, IN (December 1, 2008)- A study published in the American Journal of Preventive Medicine demonstrates that the effect of greenness on weight status is independent of residential density. Presence of parks, playgrounds and green assets were more of a factor, especially for children, in lower rates of obesity than density or measures of walkability.
Physical activity is one obvious pathway through which urban vegetation might influence the BMI of children and youth. Unlike adults, children and youth in urban environments may be active in a wider variety of open spaces (e.g., yards, parks, vacant lots) and less likely to constrain activity to streets and sidewalks.
The built environment is emerging as important for obesity prevention; however, most studies are adultcentric and cross-sectional. Among adults, the within-neighborhood availability of supermarkets is positively associated with the consumption of fruits and vegetables and inversely associated with obesity. In other studies, street connectivity, land-use mix, and residential density are associated with moderate physical activity, while urban sprawl is related to obesity and inversely related to walking.
Among children and youth, physical activity is positively associated in most but not all studies with time spent outdoors and with proximity to recreational facilities and parks. In one study, land-use mix, residential density, and recreational amenities were not associated with adolescent girls’ BMI. In a longitudinal study, urban sprawl was not associated with adolescent BMI in the longitudinal context, but the contemporaneous relationship was significant.
Given the importance of parks and time spent outdoors, neighborhood greenness could be associated with the BMI of children and youth as an indicator of access to spaces that promote physical activity. In one cross-sectional study, higher greenness was associated with lower child and youth BMI, but only in areas with high population density. Greenness is inversely correlated with residential density that is, in turn, associated with physical activity and BMI in observational studies of adults. Greenness and residential density are modifiable attributes of the built environment; however, it remains unknown whether each has independent effects on the BMI of children and youth.
Understanding the independent and relative influences of residential density and greenness on the BMI of children and youth is an essential first step toward targeted preventive intervention. If density is distinct and more influential than greenness, then urban development that encourages highly connected street networks, mixed commercial and residential land use, and concentrated housing would be warranted. If greenness is more important, then the creation or preservation of open green spaces would be indicated instead of high-density development. If both variables are significantly associated with the BMI of children and youth, then urban-development schemes that encourage density while preserving greenness would be required.