Urban green space and obesity in older adults: Evidence from Ireland

Abstract

We examine the association between living in an urban area with more or less green space and the probability of being obese. This work involves the creation of a new dataset which combines geo-coded data at the individual level from the Irish Longitudinal Study on Ageing with green space data from the European Urban Atlas 2012. We find evidence suggestive of a u-shaped relationship between green space in urban areas and obesity; those living in areas with the lowest and highest shares of green space within a 1.6 km buffer zone have a higher probability of being classified as obese (BMI ⩾30). The unexpected result that persons in areas with both the lowest and highest shares of green space have a higher probability of being obese than those in areas with intermediate shares, suggests that other characteristics of urban areas may be mediating this relationship.

Characterising urban green space density and footpath-accessibility in models of BMI

“…However, the association loses statistical significance if the buffer size is reduced to 800m or if green areas that are located adjacent to walkable roads are used, despite relatively high correlations among respondent exposure rankings using the various buffer types. While the associations we report are not statistically significant in most cases, our model coefficients do broadly follow a u-shape, consistent with previous work carried out by Dempsey et al (17) in a similar context. This suggests that the incorporation of footpath availability measures into the analysis does not offer a full explanation for their results.…”

“…In addition, our results emphasise the sensitivity of existing results in the literature to the characterisation of green space. While we do find that estimated exposure to the lowest quintile of green space in a 1600m footpath-accessible network buffer is associated with higher BMI scores, it is clear that an adjustment for footpath-accessibility of urban green space, as we have defined it, has not offered a complete explanation for the u-shaped relationship previously identified in these data by Dempsey et al (17).…”

“…Although we observe a positive relationship between quintiles 4 and 5 (highest) and BMI, these coefficients are not statistically significant. The inclusion of footpath-accessibility measures into a 1600m network buffer thus weakens the positive association between high exposure to green space and BMI found by Dempsey et al (17) but does not completely remove the pattern. Indeed, it is noteworthy a more parsimonious version of this model (Model 2) which drops groups of covariates that are collectively insignificant at the 5% level, produces a slightly stronger u-shaped relationship with marginal statistical significance observed on the quintile 4 and 5 coefficients.…”

“…Failure to do so could lead to overestimation of a positive relationship between greenness and health (13). Our full set of control variables closely follows Dempsey et al (17) and includes age category, urban location, gender, income category, employment status, marital status, highest level of educational attainment, medical cover, smoking status, and a dummy variable that indicates reported difficulty walking 100m. Descriptive statistics for these variables appear in Table 1.…”

“…Since our observed results may be sensitive to this choice, we perform our analysis using multiple buffer extents. Our main specification follows Dempsey et al (17) in using a 1600m buffer, which creates a zone roughly appropriate for a 20-minute walk from one's home address. We then repeat the statistical analysis with a smaller 800m buffer.…”