Public Parks and Shady Areas in Times of Climate Change, Urban Sprawl, and Obesity

Skin cancer remains one of the most common cancers globally despite its being highly preventable. The primary risk factor for skin cancer is ultraviolet radiation (UVR) from the sun or indoor tanning. Skin cancer prevention behaviors include avoiding indoor tanning; seeking shade, especially during midday; and wearing protective clothing and sunscreen. There is some evidence that, when used properly, shade is more effective than sunscreen in reducing UVR exposure (e.g., in the form of sunburns).¹ Other advantages to using shade as a public health intervention include its potential reach and sustainability in that relatively permanent shade structures can be built that can protect many people over a period of several years.

In this issue of AJPH, Buller et al. (p. 1869) report on a randomized controlled trial investigating the effect of shade sails (that block ≥ 94% of UVR) on use of passive recreation areas (PRAs) in Denver, Colorado, and Melbourne, Australia. On the basis of observational data collected during summertime (June to September in the United States, and December to March in Australia), it was found that park-goers’ use of PRAs randomized to shade was significantly higher than their use of control PRAs (odds ratio [OR] = 3.91). Shaded PRA use increased more in Denver than in Melbourne (OR = 2.92).

METHODOLOGICAL STRENGTHS

Buller et al. note that this is only the second prospective randomized controlled trial of purpose-built shade for sun protection, the first of which was conducted by members of the same team, albeit in school settings. The study possesses a number of important methodological strengths, including being a randomized controlled trial, using observational data collection, controlling for a number of factors that could have influenced outcomes (e.g., weather during observations, park amenities, demographic characteristics of local residents), and being conducted in two countries. Another methodological strength was the stratified randomization based on several important factors: city, data collection wave, and pretest PRA use. A final strength was that, in addition to randomizing parks to intervention or control, data from a second PRA within each park were collected for use as a covariate. Completing this yeoman’s task of assessing 145 public parks is admirable, as it was undoubtedly budget-, time-, and labor-intensive, and required extensive planning in terms of design and methodological decisions (e.g., to collect more than 1000 in-person observations, as well as working closely with municipal staff and shade sail vendors in two countries). There are few, if any, other teams worldwide who could have successfully completed this work.

In addition, the comprehensive nature of the study report is consistent with calls from scientists and scientific bodies such as the National Institutes of Health to enhance scientific reproducibility through rigor and transparency.² For example, one of the very useful aspects of the report by Buller et al. is that the authors discuss some challenges they encountered, which does not always happen but can enhance the credibility of findings and inform similar future research and public health endeavors. For example, they described how, when, and why a change in sample size and primary outcome was made. Furthermore, Buller et al. found the opposite of one of their hypotheses: PRA use increased more in Denver than in Melbourne. The authors discuss several potential reasons for this. The most likely reason seems to be that Melbourne probably already had more options for shade before the intervention, both because of the climate’s greater ability to support shade trees and its long-term comprehensive community-wide sun-safety campaign, thus reducing the ability to demonstrate intervention effects there.

STUDY LIMITATIONS

Although outweighed by the aforementioned major strengths, there are a few limitations, as also noted by the authors. These include the study’s being conducted in only two locales, with some notable differences such as Australia’s relatively strong norms around skin protection and Denver being more urban than Melbourne. The other limitation mentioned by the authors was that it was not known whether specific individuals using the intervention PRAs at posttest demonstrated greater sun protection than they would have otherwise or, in other words, whether they used shade sails instead of using an unshaded rather than another shaded area within the same large park. In addition, only 36 parks were randomized to receive shade sails, most likely for feasibility and budgetary reasons, although three times as many parks were randomized to the control condition, presumably to enhance statistical power.

FUTURE DIRECTIONS

Public parks and shady areas may become even more important with ongoing climate change, further urban sprawl, and increasing obesity prevalence. Large-scale public health interventions such the one described by Buller et al. (as opposed to individually based interventions) have been found previously to have significant effects on health-related behaviors such as indoor tanning and sunscreen use (see review by Sandhu et al.³). However, despite the statistically significant effects in the current study, a small absolute number of people used the PRAs during data collection periods and were, therefore, protected by the shade sails. Buller et al. discuss potential reasons for this and some factors associated with greater use of shade. Studies simultaneously focusing on sun exposure, skin protection, physical activity, and sedentary behaviors and their relationships could be helpful in further investigating and increasing the use of shaded recreation areas, both passive and active. Work along these lines is already under way by members of the study team.⁴

The reason there are not more shade structures currently is primarily, in all likelihood, because of their cost. Thus, investigating issues around cost would be quite useful. Cost data could be presented in future publications potentially along with details about the process of building shade structures—for example, barriers and facilitators to initiation and completion. Perhaps cost comparisons could be conducted to investigate the potential cost of building and maintaining shade structures compared with other types of skin cancer prevention, detection, or treatment efforts. Studies have previously shown that skin cancer (and other types of) prevention efforts (e.g., policy implementation, educational campaigns) are highly cost-effective (see review by Gordon and Rowell⁵). Buller et al. rightly point out that such scientific evidence needs to be communicated effectively to urban planners and government officials, as well as other stakeholders such as the public, so that evidence-informed decision-making can occur to maximize public health cost-effectively. Information about desirable characteristics of shade structures in different environments that could be useful for these stakeholders is also available (see review by Parisi and Turnbull⁶).