Association Between Ambient Air Pollution and Diabetes Mellitus in Europe and North America: Systematic Review and Meta-Analysis

Ikenna C. Eze; Lars G. Hemkens; Heiner C. Bucher; Barbara Hoffmann; Christian Schindler; Nino Künzli; Tamara Schikowski; Nicole M. Probst-Hensch

Disclosures

Environ Health Perspect. 2015;123(5):381-389. 

In This Article

Abstract and Introduction

Abstract

Background Air pollution is hypothesized to be a risk factor for diabetes. Epidemiological evidence is inconsistent and has not been systematically evaluated.

Objectives We systematically reviewed epidemiological evidence on the association between air pollution and diabetes, and synthesized results of studies on type 2 diabetes mellitus (T2DM).

Methods We systematically searched electronic literature databases (last search, 29 April 2014) for studies reporting the association between air pollution (particle concentration or traffic exposure) and diabetes (type 1, type 2, or gestational). We systematically evaluated risk of bias and role of potential confounders in all studies. We synthesized reported associations with T2DM in meta-analyses using random-effects models and conducted various sensitivity analyses.

Results We included 13 studies (8 on T2DM, 2 on type 1, 3 on gestational diabetes), all conducted in Europe or North America. Five studies were longitudinal, 5 cross-sectional, 2 case–control, and 1 ecologic. Risk of bias, air pollution assessment, and confounder control varied across studies. Dose–response effects were not reported. Meta-analyses of 3 studies on PM2.5 (particulate matter ≤ 2.5 μm in diameter) and 4 studies on NO2 (nitrogen dioxide) showed increased risk of T2DM by 8–10% per 10-μg/m3 increase in exposure [PM2.5: 1.10 (95% CI: 1.02, 1.18); NO2: 1.08 (95% CI: 1.00, 1.17)]. Associations were stronger in females. Sensitivity analyses showed similar results.

Conclusion Existing evidence indicates a positive association of air pollution and T2DM risk, albeit there is high risk of bias. High-quality studies assessing dose–response effects are needed. Research should be expanded to developing countries where outdoor and indoor air pollution are high.

Introduction

Ambient air pollution ranks high among risk factors for the global burden of disease (Lim et al. 2012), and is linked to several chronic noncommunicable conditions such as cardiovascular diseases (Bauer et al. 2010; Brook et al. 2010; Künzli et al. 2010), asthma (Bui et al. 2013; Jacquemin et al. 2012; Künzli et al. 2009), chronic obstructive pulmonary diseases (COPD) (Andersen et al. 2011; Schikowski et al. 2014; Zanobetti et al. 2008), and cancers including lung (Raaschou-Nielsen et al. 2013a), cervical, and brain cancers (Raaschou-Nielsen et al. 2011). Persons with type 2 diabetes mellitus (T2DM) are at increased risk to develop micro- and macrovascular diseases and reduced lung function (Jones et al. 2014; Kinney et al. 2014). Air pollution has also been shown to be more detrimental to diabetic patients, worsening their clinical outcomes (O'Neill et al. 2005; Raaschou-Nielsen et al. 2013b; Whitsel et al. 2009; Zanobetti and Schwartz 2001).

More recent evidence is supportive of an air pollution effect on diabetes risk. Experimental evidence show that possible pathways may include endothelial dysfunction, overactivity of the sympathetic nervous system (Rajagopalan and Brook 2012), immune response alterations in visceral adipose tissues; endoplasmic reticulum stress resulting in alterations in insulin transduction (Sun et al. 2009), insulin sensitivity, and glucose metabolism; and alterations in mitochondria and brown adipocytes (Liu et al. 2013; Rajagopalan and Brook 2012).

Papazafiropoulou et al. (2011) systematically reviewed the etiologic association between environmental pollution and diabetes, taking into account studies on organic pollutants and secondary effects of air pollution on diabetic patients published up to November 2010. They described a positive association between environmental pollution and prevalent diabetes, as well as increased morbidity and mortality among diabetic patients. A number of pertinent studies have been published since this review, and thus far there is, to the best of our knowledge, no meta-analysis of the available evidence. We therefore systematically identified and reviewed the epidemiological evidence on the association between air pollution and diabetes mellitus, and synthesized the results of studies on the association with T2DM.

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