Respondents who lived further from urban green spaces in this study were less likely to visit them than those nearby, and this effect was particularly strong for Formal green spaces. Respondents living further from green spaces were also less likely to meet guideline physical activity levels and more likely to be overweight or obese, even after adjustment for the walkability of respondent’s neighbourhoods, their socioeconomic status, and area deprivation. Importantly, when the outcomes were examined against frequency of green space use, trends were apparent whereby more frequent green space users were more physically active and less likely to be overweight or obese. The robustness of these associations was tested by controlling for a wide range of characteristics of the areas around respondent’s homes which were hypothesised to potentially be associated with each outcome. Subsequent associations were mostly attenuated but persistent, except for those with bodyweight which generally disappeared. This may reflect the particularly varied nature of the personal, societal, and environmental influences on weight.
The reasons for the apparent importance of Formal green spaces warrant some attention. The associations with Formal green space use could be artefactual if respondents were more likely to consider this type of green space when they completed the survey, which asked them to state how often they visited a ‘green space or park’ but did not define these terms. However, this would not explain our observed associations with the physical activity and bodyweight outcomes. It may be therefore that the attributes of Formal green spaces make them particularly suitable for physical activity. They often have a good path network, which provides a basis for a range of activities including walking, cycling and jogging (Kaczynski, Potwarka, & Saelens, 2008
), and the presence of paths may also encourage active forms of travel as people may be more inclined to walk or cycle to destinations if they can incorporate a green environment into part of their journey (Giles-Corti et al., 2005
). In addition, these spaces are often well maintained and are sometimes lit, and this may improve perceptions of their safety. Finally, the diverse nature of Formal green spaces means they tend to offer a suitable environment for a broad range of people, whilst those provided for sport for example are often specialised, housing specific facilities, and are used by a small proportion of the population (Handy & Neimeier, 1997
Our findings have implications for urban planning. Although UK planning policies such as Planning Policy Statement 3 (Department for Communities and Local Government, 2006b
) now stipulate that green spaces should be incorporated into urban planning, there are currently no minimum requirements to ensure these guidelines are sufficiently met. Nevertheless, there have been some recommendations for the level of green space provision that might be appropriate. These suggest that people in urban areas should be able to access a green space of at least 2 hectares in size within 300m or a 5 minute walk of their home (English Nature, 1995
). Our results suggest that better access to green spaces may be associated with higher use and in turn greater participation in physical activity which could reduce levels of obesity. Our finding of particularly strong associations with access to Formal parks suggests that the green spaces should be well maintained and suitable for use by a broad spectrum of the population, both key characteristics of this type of space.
Our study has a number of strengths and weaknesses. One of the strengths was the large sample size of almost 7,000 respondents. In addition, the sample purposively included a mix of respondents of different socioeconomic status, being representative of the overall population of Bristol. We had information on actual green space use amongst respondents and detailed information on the provision of green space in the city. We also had details of both the physical activity and bodyweight of respondents.
In terms of weaknesses, one of the limitations of the study was that the outcome measures of green space visits, physical activity, and weight were all based on simple self-report. There are a number of consequences of this. Firstly, we are not able to determine whether reported frequency of green space use was a valid measure of actual use, or if that use actually took place in those spaces for which we calculated objective accessibility measures, although the fact it was found to be strongly associated with our objectively computed measure of green space accessibility in the manner expected is reassuring. Furthermore, we were unable to validate our measure of physical activity participation, and it is noteworthy that reported physical activity levels were somewhat high compared to overall population estimates, with 39% of our sample reporting undertaking physical activity at least 5 times a week. Nevertheless we are reassured by the fact that Jackson, Morrow, Bowles, Fitzgerald, & Blair (2007)
have recently shown acceptable levels of validity in a single item report measure similar to that used here. We were also unable to validate our measure of BMI and there is evidence that the use of self-reported height and weight for the calculation of BMI can lead to under-reporting of weight in particular, although research evidence also suggests that self report based measures are valid (e.g. Elgar & Stewart, 2008
) and we have no reason to believe that any under-reporting would be associated with access to green spaces, and thus bias our results.
Whilst the response rate of 34% was typical of postal surveys, it may be that respondents were not typical of those who did not reply, although the focus of the survey was not specifically on the outcomes studied so non-response bias may have been small. A further limitation is that the study is cross sectional in nature and hence it is difficult to determine if the relationships we have observed are causal. In particular, it may be that those members of the population who are more active in general choose to reside in areas with better access to green space, in which case the presence of the green spaces may not be encouraging physical activity per se. However, it is noteworthy that the relationships were generally apparent after adjustment for both individual and area socio-demographic factors. We also tested their robustness by controlling for a particularly wide variety of neighbourhood measures. We delineated neighbourhoods based on an 800m distance from respondent’s homes. Whilst this distance compares with that used by other researchers, it may be that our results are sensitive to the definition used, although a sensitivity analysis on the road connectivity variable using radii of 400m and 1600m showed that the associations observed with the three outcomes were stable. Furthermore, although we had information on the types of green space present in Bristol we did not have detail on the specific features of each. A valuable extension to this work would be to better understand which features might be acting to encourage physical activity, as this insight could be used to inform the design of new green spaces and the regeneration of existing ones.
This study has provided new evidence that good access to urban green spaces is associated with higher use, higher physical activity levels, and a lower likelihood of being overweight or obese. Informal physical activity is an important component of overall activity levels, and provision of facilities such as green spaces which can be used for a wide range of physical activities, has population wide benefits. It is important that supportive environments are available to facilitate active lifestyles, and our findings suggest that green spaces may provide a valuable resource in urban areas.