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The recent increase in childhood obesity is expected to add significantly to the prevalence of chronic diseases. We used multivariate multilevel analysis to examine associations between parks/green space and childhood overweight/obesity across communities in Calgary, Canada, a city characterized by intensified urban sprawl and high car use.

Body Mass Index was calculated from measured height and weight data obtained from 6,772 children (mean age = 4.95 years) attending public health clinics for pre-school vaccinations. Each child's home postal code was geocoded using ESRI ArcGIS 9.2. We examined four measures of spatial access to parks/green space (based on Geographic Information Systems): 1) the number of parks/green spaces per 10,000 residents, 2) the area of parks/green space as a proportion of the total area within a community, 3) average distance to a park/green space, and 4) the proportion of parks/green space service area as a proportion of the total area within a community. Analyses were adjusted for dissemination area median family income (as a proxy for an individual child's family income) community-level education, and community-level proportion of visible minorities.

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In general, parks/green space at the community level was not associated with overweight/obesity in Calgary, with the exception of a marginally significant effect whereby a moderate number of parks/green spaces per 10,000 residents was associated with lower odds of overweight/obesity. This effect was non-significant in adjusted analyses.

Limitations of earlier studies on the relationship between obesity and the built environment in children include a reliance on self or parent reported data for BMI, a lack of objectively measured data for physical features of the environment, and limited discussion of how associations may be context-specific; for example, presence and proximity of parks may be important in areas with high pedestrian activity but less important in car-dominated areas. The study undertaken addresses these limitations by using measured height and weight data for a large representative sample of children and Geographic Information Systems (GIS) to objectively measure four dimensions of spatial access to parks/green space. GIS has proven valuable when studying spatial access to parks [29, 30] and elements of the built environment that relate to obesity[31].

The aim of this study is to examine the association between spatial access to parks/green space, measured in four different ways, and childhood overweight/obesity in the specific context of Calgary, Canada. We focus our analysis on spatial access to parks/green space by including measures of ease with which parks/green space can be reached (e.g., distance) as well as the proportional area or number of parks/green space within communities. Calgary is one of Canada's major metropolitan areas and is characterized by rapid population growth, which has led to intensified urban sprawl. According to recent data from Statistics Canada, Calgary is a city characterized by more car travel than nearly all other major Canadian centres [32, 33] and thus provides a unique opportunity to examine these associations and explore the conditions under which specific built environment features may or may not matter.

Parks/green space in this study refers to all public parks, schools (i.e., school fields) and recreation areas (e.g., public riverfront) within the city (data retrieved from the City of Calgary [39]). Parks/green space that were greater than one km2 (e.g., provincial parks) were deemed to serve the entire population of the city [40] and were removed from this analysis. Our first measure of access to parks/green space was a simple count of the number of parks/green space (based on their area centroid) per 10,000 residents (based on the 2001 population). Our second measure represented the geographic area (km2) of parks/green spaces as a proportion of the total area within a community. To account for the likelihood that people cross community boundaries to visit nearby parks/green space we used two additional measures of access to parks/green space applying current GIS methods[29]. Our third measure was the average distance to the nearest park/green space. The Network Analyst extension of ArcGIS 9.2 was used to determine the distance from each child's residential postal code location to the nearest park/green space centroid. The average of these nearest distances was calculated for each community. Distance was calculated along the road network using the DMTI Spatial CanMap RouteLogistics file[41]. Our fourth measure of parks/green space access was the proportion of park/green space service area as a proportion of the total area within a community. Network Analyst was used to create 800 meter service areas around each park/green space based on the CanMap RouteLogistics file[41]. This distance has been specified as the maximum distance residents will walk to reach a community park/green space in a Canadian city with similar geographic characteristics to Calgary[29]. This index gives us insight into the amount of area serviced by a particular park/green space, while taking into account the crossing of boundaries.

We applied multivariate multilevel regression methods to quantify the association between each of the four parks measures (second or community-level) and childhood overweight/obesity (first or individual-level), adjusting for first- and second- level covariates. Multilevel analytic methods can account for the clustering of children's observations within communities and allow for estimation of the effects of both individual-level and community-level variables[7, 42]. We combined the overweight and obese categories due to the small number of children classified as obese (4.5%). Our model was a two-level, random-intercept logistic regression with childhood overweight/obesity as the binary outcome (1 = overweight/obese; 0 = normal or underweight). Sex and dissemination area median family income (proxy for individual family income) were considered as individual-level covariates. For our four measures of parks/green space, we treated the variable as continuous when the distribution appeared normal, and created tertiles when the distribution was markedly non-normal. Each park variable was examined separately. Community-level education and proportion of visible minorities were examined as community-level covariates.

Of this sample, 16.1% of children were either overweight or obese (16.3% girls, 15.9% boys). We had information on 1,559 of the children removed from the analysis and these children were not significantly different from those included in regards to sex or overweight/obesity proportion. Within Calgary's boundary, there were 862 areas designated as 'public park, school or recreation' covering 79 km2 or 10.9% of the city's total area. Once the larger parks/green spaces were removed, 852 parks remained for inclusion in the analysis covering 42 km2. Our four measures of parks/green space access had the following distributions: number of parks/green space per 10,000 residents (range 0 to 150.7), proportion of parks/green space area (range 0 to 23%), average network distance to a park/green space (256.2 to 4,639.2 m), and proportion of parks/green space service area (0 to 100%).

The random intercept model allowed us to first ascertain that there was significant between-community variation in the outcome variable (overweight/obesity); p =

Figure 1 illustrates the patterns for a) overweight/obesity across Calgary and b) number of parks/green space per 10,000 people by community. There is a clear pattern whereby communities that have more overweight/obese children tend to be in the lowest tertile for number of parks/green space per 10,000 people. Figure 2 illustrates a) proportion of visible minority by community and b) proportion with at least a completed Bachelor's degree by community. Figure 2 illustrates that the marginal finding for having a moderate versus low number of parks/green space per 10,000 people, in the partially adjusted model is a result of the patterns for community-level education and proportion of visible minority.

To explore the possibility that the influence of parks/green space variables differed by sex, or by income, we conducted post hoc testing of each parks/green space variable as a predictor of the sex-overweight/obesity association, and the income-overweight/obesity association. In no instance were significant interactions detected (data not shown).

We examined the associations between four measures of spatial access to parks/green space at the community level and childhood overweight/obesity in Calgary, Canada. Overall, our results suggest that spatial access to parks/green space per se has a limited direct association with childhood overweight/obesity in this context. Nonetheless, our findings raise some interesting discussion points. 2ff7e9595c