In the present study, we examined the relationship of 12-year-old student overweight and obesity-related behaviour with spatial accessibility to PA facilities and to food outlets, estimated by GIS methods. We specifically explored the hypothesis that such relationships are modulated by individual and environmental SES characteristics. Our main findings provide support for an individual/environment interaction. When spatial accessibility to urban PA facilities or to general food outlets was low, there was an increased likelihood of being overweight in blue-collar-workers children but not in children from higher socio-occupational categories. Consistent with existing evidence,9, 35
the association of spatial accessibility to PA facilities with regular supervised PA, independently of individual and environmental SES characteristics, indicates that PA level might partly mediate the effects of environmental SES on youth overweight.
The strengths of our study lie in the high-participation rate and the only one age group, which limited variability related to age-related behavioural changes observed during adolescence, along with measured BMI and assessment of both PA and food environments. Moreover, we measured environmental characteristics and spatial accessibility to food outlets across continuous space using sophisticated geographical methods to estimate spatial accessibility, without relying on arbitrary administrative boundaries. Some limitations to the study should be mentioned. First, we used cross-sectional data and could not make direct causal inferences. Second, regular supervised PA and dietary measures were self-reported, with relatively crude and non-exhaustive questions concerning diet. Third, this study is based on secondary analysis of pre-existing data. Therefore, information on spatial accessibility to PA facilities was limited and was only available at the municipality level. Although the food outlets variables were more detailed, they were subject to measurement error because of potential inaccuracies in the commercial database used. Moreover, we had no information on other components of accessibility (organisational, economic and qualitative), nor on other PA-related elements, including security and walkability indices.
Numerous physical and built environment features have been associated with PA in a growing body of literature.13, 36
Few studies have examined the impact of the built environment on youth obesity, and the possible relationship between the built environment and weight status remains subject to debate.5, 8, 10, 11, 12
In a recent review,9
we found that the inverse relationship between youth weight and indices indicating higher walkability was the most consistent. Contrary to observations in adults, but consistent with our results showing no association between overweight and spatial accessibility to nature PA facilities, parks and ‘green areas' were generally not strongly associated with youth BMI. Recent data showing that park users are primarily very young children and adults suggest that this type of setting may be less important for PA in older children.37
A beneficial relationship between weight and spatial accessibility to PA facilities has been reported in only four out of nine papers.9
However, we should emphasise that about half of the negative papers did not control for environmental or individual SES. Only one study15
adjusted for both, and it found that the number of schools (as potential sites of PA practice) inaccessible on weekends was higher in neighbourhoods with lower SES and was independently associated with significantly higher BMI. Yet, as emphasised by socio-ecological models of behaviour, spatial accessibility is only one of multiple determinants of a healthy lifestyle and health itself. On the other hand, a more favourable socio-economic context and denser social networks might influence the built environment.23
Previous studies38, 39
have found a higher number of PA facilities in more affluent places of residence. However, such relationships are not clear-cut and may be context specific. In two European studies,24, 40
associations between environmental SES and the presence of PA facilities, or comfort-specific characteristics of such facilities, were found to vary from positive to negative depending on the facility. Nevertheless, inter-relationships between built and socio-economic characteristics may result in confounding the association between differing environmental exposures,41
and, as such, both categories of environmental determinants should be included in the analyses.
The current study extends previous research on the effects upon health of spatial accessibility to different facilities by specifically examining cross-level interactions among built environmental characteristics and environmental or individual SES. To our knowledge, no previous study had specifically addressed this issue in relation to PA facilities and youth overweight. Although more research is needed to delineate the exact mechanisms underlying the interactions observed here and to better identify policy-relevant target populations and determinants, our results suggest that disadvantaged children may be more dependent on local environmental determinants than their more favoured counterparts.
Interestingly, we found an analogous interaction between individual SES and spatial accessibility to general food outlets. These results are consistent with existing data indicating that an inverse relationship between overweight and the density of supermarkets, thought to offer a higher variety of healthy food choices, depends on individual characteristics that might reflect SES, such as ethnic origin and mothers employment conditions.42
Similarly, a positive relationship with convenience stores in low-income towns was found in one study,20
whereas in another study, a positive relationship with fast-food outlets availability was found for a low SES population living in East Harlem, New York.19
In contrast to data on the association between spatial accessibility to PA facilities and regular supervised PA, we found no relationship between spatial accessibility to general food outlets and dietary behaviours. Our crude measurement of dietary behaviour may explain, at least in part, this negative result. It may also reflect the fact that the food environment is complex. Organisational characteristics, such as store opening hours, food quality, prices and parental choices, may be as important as spatial accessibility to food outlets and should be taken into account in future research. These characteristics vary according to country and culture, indicating that future studies should be carried out in various geographical and socio-economic settings. Moreover, we cannot exclude the possibility that the relationship of PA and food environment variables with weight is indirect and may reflect other contextual obesity determinants, such as higher walkability or more dense social networks in commercially attractive neighbourhoods.43
In conclusion, our data add to the growing body of evidence documenting relationships between the built environment and health outcomes, including youth overweight, by demonstrating specific interactions between individual and environmental factors in shaping health and health-related inequalities. Although more research is necessary to determine whether these interactions are context-specific, present results may be relevant for influencing health policies and urban planning at both a national and local level.