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.
First, we observed marginal significance in the partially adjusted model where children living in communities with a moderate number of parks/green space per 10,000 people had lower odds of being overweight/obese compared to those living in communities with a low number of parks/green space per 10,000 people. In the fully adjusted model the effect was slightly reduced and became non-significant. Although our finding for number of parks/green space per 10,000 was small and non-significant we feel that this finding merits a brief comment given the local circumstances in Calgary. Currently, the City of Calgary's planning guidelines advocate the development of one centrally located park within new communities as opposed to several small parks. Given the possibility that the number of parks/green space in and around a child's community may be associated with childhood overweight/obesity our results raise the suggestion that City guidelines should be periodically reconsidered.
However, we have to keep in mind that the effect of the number of parks/green space per 10,000 residents was not significant once we controlled for community-level education and proportion of visible minorities, speaking to the importance of these sociodemographic circumstances in relation to obesity as identified in other studies[47, 48]. For example, Janssen and colleagues (2006) found that children living in communities with a high percentage of residents with less than a high school education had an increased likelihood of both obesity and unhealthy eating. Since education can be used as a proxy for health literacy  it may represent a community's collective set of attitudes and beliefs about obesity including social norms related to diet and/or exercise in a community. Review articles have discussed how U.S. communities with a high proportion of minorities have reduced neighbourhood access to supermarkets that provide access to a mix of healthful food products at reasonable cost and higher than average exposure to fast food restaurants [51, 52] all of which may contribute to childhood obesity. These findings suggest that both ethnic and education factors at the community level (including culture, norms and health knowledge, beliefs, values and behaviours) are likely important factors in determining obesity risk.
Examining our individual-level variables in all of our models, we observed that DA income (as a proxy for individual family income) was negatively associated with overweight/obesity though the effect was small. This finding is consistent with Canadian studies that have shown an inverse association between various measures of family and/or household income (e.g., parent reported household income, youth perceived family wealth) and childhood obesity risk [47, 53, 54]. Recent studies provide several plausible explanations for the association between family and/or household income and childhood obesity. First, children from higher income families are more likely to have a family structure including two parents  who are more involved in their physical activities and also have the time to frequent other activities with them. Additionally, two-parent families typically include a father in the home, and a recent review highlighted that fathers have been shown to be the most important role model for physical activity in young children. Children from families with a higher income may also be more likely to have access to other important determinants of body weight including healthy foods [27, 57] and have more opportunity to participate in organized sports and other physical activity pursuits that are often costly and require parental support[58, 59]. Overall, our finding that higher family income (even when using DA level income as a proxy) is associated with reduced risk of overweight/obesity in children is consistent with the above Canadian studies.
Our other measures of parks/green space access, proportion parks/green space area, average network distance to the nearest park/green space, and proportion of parks/green space service area were not associated with childhood overweight/obesity. Our null findings on these variables differed from findings of two recent studies that have reported that greater neighbourhood park access was associated with lower risk of overweight/obesity[26, 27]. These inconsistent findings may reflect differences in our methodologies with one of the above studies examining access to a variety of physical activity facilities combined with parks and obesity in grade 7 to 12 students  and the other examining parent's subjective measures of park access and overweight/obesity in grade 5 students . Methodological considerations may also explain our null finding for proportion of parks/green space service area. While the use of this particular variable is common in the spatial accessibility literature  there is an issue with this measure in the context of Calgary. Parks/green space service area does not account for community size and bases its measure on number of parks/green space as opposed to size of the parks/green space. Therefore, this measure may not be appropriate for use in cities, like Calgary, where community size varies drastically. We also found no significant association for proportion of parks/green space but note that this may have resulted from the small range and thereby relatively equitable distribution of proportion of parks/green space across Calgary communities.
Our null finding for average distance to a park/green space is consistent with another study that found no association between average distance by street travel to the nearest park and childhood obesity in a population of US low-income pre-schoolers. Additionally, this null finding supports the idea that average distance to parks/green space may not be an important feature of the built environment in communities like Calgary that are characterized by high car use. A recent Canadian study showed that, while 49% of parents reported frequenting the park closest to their home, the majority of respondents reported travelling more than 4 km to get to their desired park. For those parents who chose to travel to a park, park location was not as important as park amenities. Given that Calgary is a city characterized by a high amount of car travel, it seems plausible that whether parks are nearby or not is perhaps irrelevant to many Calgarians, who would opt to drive to a more desired park [32, 33] or to drive their child to organized activities.
Considering the consistency of our null findings across all of the fully adjusted models, it is possible that spatial access to parks/green space is truly not pertinent to overweight/obesity in young children living in cities similar to Calgary. This conclusion is supported by another Canadian study, conducted in a city comparable to Calgary, that found no association between the number of physical activity facilities, including parks and playgrounds, and childhood overweight/obesity in a similar population of young Canadian children. It is also possible that our findings reflect a disconnect between physical activity and obesity; namely, perhaps our measures of parks/green space access has implications for physical activity in Calgary (which we did not measure), but that its implications do not show up when we examine overweight/obesity. This would be an important question for future research. Also important is the fact that access to parks/green space does not equal utilization and therefore gaps remain in terms of clarifying the associations between access to parks/green space, actual usage, and the implications - if any - for weight. It is also possible that Calgary's climate, characterized by long and sometimes very cold winters precludes parks/green space, despite their location, from being an important resource for children.
One limitation of our study is the temporal disconnect between census data (from 2001, the most current available at time of writing) and the height and weight data which were collected in 2005. As a result, some children's postal codes corresponded to a community that had not been developed at the time of the 2001 census. These children had to be excluded from the analysis, which led to a reduction in the effective sample size both for children and for communities. Another limitation is that not all families choose to vaccinate their children and it is possible that these families are of lower socioeconomic status. Since there is evidence to suggest that children of lower SES may be at increased risk of overweight/obesity [47, 53, 61] this study may underestimate the prevalence of overweight/obesity and may be underestimating the effects of parks/green space access on childhood overweight/obesity. And finally, the cross-sectional nature of the data clearly precludes discussions about causality. Strengths of this study include the high quality of the height and weight data, which were obtained from directly measuring a large number of Calgary children reporting to vaccination clinics. Also, the use of GIS allowed for full coverage of Calgary and objectively measured data for each parks/green space variable. Furthermore, this study's examination of four different measures of spatial access to parks/green space allowed us to tap into the breadth of ways to measure parks/green space access.
There is an important opportunity to further this line of research by examining ongoing development of new communities in relation to the overweight/obesity status of children. This is especially relevant in the Calgary context, since the city is experiencing tremendous growth with many new community designs being constructed. Thus, Calgary's unique context provides an important opportunity for future research to examine several characteristics of the built environment, including the effects of current park/green space planning policies. Since the development of childhood overweight/obesity is complex and multifactorial, future research studies need to examine a more exhaustive set of possible etiological factors. Overall, the findings of this research suggest that the relevance of spatial access to parks/green space in terms of its association with childhood overweight/obesity are likely context specific and in some cities such as Calgary, having good spatial access to parks/green space may not be an important feature of the built environment.