Academic journal article Environmental Health Perspectives

Associations of Residential Long-Term Air Pollution Exposures and Satellite-Derived Greenness with Insulin Resistance in German Adolescents

Academic journal article Environmental Health Perspectives

Associations of Residential Long-Term Air Pollution Exposures and Satellite-Derived Greenness with Insulin Resistance in German Adolescents

Article excerpt

Introduction

A large proportion of the global population breathes unhealthy air (van Donkelaar et al. 2010). In addition to power plants and heavy industries, urban traffic is a major source of air pollution, especially fine particulates and gaseous compounds (Krzyzanowski et al. 2005). A reduced life expectancy, mainly attributable to respiratory and cardiovascular disease, has been documented among individuals exposed to ambient air pollutants in many regions of the world (Beelen et al. 2014; Heinrich et al. 2013; Lepeule et al. 2012; Yorifuji et al. 2010). To date, no "safe limit," at which no health effects are observed, has been identified. Indeed, exposures below the current air quality standards have been associated with adverse health effects in large cohort studies in the United States (Miller et al. 2007) and a study of > 300,000 European adults (Beelen et al. 2014).

Compared with those for all-cause mortality and cardiovascular disease, links between type 2 diabetes and air pollution have been less extensively studied in the past, even though it is believed that the same biological mechanisms--oxidative stress and systemic inflammation (Lodovici and Bigagli 2011; Thompson et al. 2010)--play a role in cardiovascular disease and type 2 diabetes development. More recently, many epidemiological studies have been summarized in systematic reviews and meta-analyses (Balti et al. 2014; Janghorbani et al. 2014; Park and Wang 2014; Thiering and Heinrich 2015; Wang et al. 2014). Taken together they provide sufficient evidence for a role of air pollution in type 2 diabetes in adults, especially for long-term exposure. We previously observed increased insulin resistance for participants with higher air pollution exposure in an analysis that included 400 children 10 years of age from the GINIplus and LISAplus birth cohorts (Thiering et al. 2013).

However, residual confounding is always possible in epidemiological studies; higher residential air pollution concentrations are often associated with lower levels of greenness. Furthermore, both factors may be associated with socioeconomic status, with effect directions depending on the study area. In addition, higher greenness (which includes green spaces such as parks and gardens, but also natural vegetation) in a neighborhood may promote a healthier lifestyle and increased physical activity while reducing other environmental impacts such as heat, noise, or ultraviolet radiation. In urban settings especially, greenness or easier access to green spaces have been linked to several diabetes-related health outcomes, such as increased physical activity (McMorris et al. 2015; Toftager et al. 2011) and well-being (Bowler et al. 2010), reduced stress (Hartig et al. 2014), improved cardiometabolic health (Paquet et al. 2013), lower blood pressure (Markevych et al. 2014), and lower body mass index (BMI) (Bell et al. 2008).

Recently, a study including > 267,000 Australian adults found a lower type 2 diabetes risk among people living in neighborhoods with more green spaces (Astell-Burt et al. 2014). However, this analysis did not confirm the prior hypothesis of the authors that better access to green spaces lowers the risk of type 2 diabetes by promoting active lifestyle and a healthier BMI. The observed reported associations for access to green space were independent of these variables. Nevertheless, it was not possible for the authors to control for air pollution exposure as well as quality and use of green spaces in their analyses. Thus, the observed association between green spaces and lower risk of type 2 diabetes may be a consequence of confounding due to lower exposure to air pollution.

In summary, for both residential greenness and air pollution, associations with metabolic diseases have been reported in adults. However, those exposures do not appear to be independent from one another. Up to now, the evidence for an association between air pollution exposure and diabetes in adults is much stronger than it is for green space, but data including both exposures are lacking. …

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