Academic journal article Environmental Health Perspectives

Improved Air Quality and Attenuated Lung Function Decline: Modification by Obesity in the SAPALDIA Cohort

Academic journal article Environmental Health Perspectives

Improved Air Quality and Attenuated Lung Function Decline: Modification by Obesity in the SAPALDIA Cohort

Article excerpt

Introduction

Air pollution is associated with impaired lung function growth in childhood and accelerated age-related lung function decline in adulthood (Breton et al. 2011). Mechanisms hypothesized to mediate the association include inflammatory and oxidative stress pathways (Andersen et al. 2011). Local as well as systemic inflammation is associated with poor lung function (Gotz et al. 2011). Persons exposed to inhaled particles from ambient air pollution develop systemic as well as pulmonary inflammation and have systemic oxidative stress, which is characterized by markers in circulating blood, bronchioalveolar lavage, induced sputum, or exhaled breath (Hogg and van Eeden 2009; Sinden and Stockley 2010).

Various markers of obesity such as weight or body mass index (BMI), as well as measures of fat distribution such as waist circumference, ratio of waist circumference to body surface area or height, percentage of fat mass, and skinfold thickness, are also related to both spirometric lung volume and flow parameters, as well as to inflammation in both blood and lung (Salome et al. 2010). The mechanisms by which excess body fat may affect lung function can be categorized as mechanical and nonmechanical (Franssen et al. 2008; Steele et al. 2009).

The mechanical effect of abdominal obesity on lung volumes and associated reductions in airway caliber is thought to be the predominant mode of action (Chen et al. 2007; Salome et al. 2010). This is supported by the observation that the ratio of forced expiratory volume in 1 sec ([FEV.sub.1]) to forced vital capacity (FVC) is usually preserved or increased, even in cases of morbid obesity. Both [FEV.sub.1] and FVC decrease in parallel with increasing abdominal obesity, even after controlling for BMI (Hickson et al. 2011). Moreover, obesity stiffens the respiratory system and increases the mechanical work needed for breathing. This is presumed to be attributable to a combination of effects on lung and chest wall compliance (Jones et al. 2007).

Inflammatory pathways may also mediate the influence of obesity on lung function (Probst-Hensch 2010). Effects of obesity on airway caliber and obstruction to air flow that were not merely explained by a mechanical effect on lung volume have been reported in a limited number of studies (e.g., Salome et al. 2010). It is hypothesized that proinflammatory adipokines produced by adipose tissue may contribute to airway remodeling in obese persons (Margretardottir et al. 2009; McClean et al. 2008; Tkacova 2010). Circulating inflammatory markers and adipokines (e.g., soluble tumor necrosis factor receptor 1, adiponectin, leptin) were inconsistently associated with respiratory function in subjects with excess body weight (Lecube et al. 2011; Thyagarajan et al. 2010). Moreover, air pollution and obesity were reported to have greater than additive effects on markers of systemic inflammation among men enrolled in the Normative Aging Study (Madrigano et al. 2009).

In light of inflammatory pathways potentially shared between air pollution and obesity (Chinn et al. 2006; Wise et al. 1998) we investigated whether the association between improved air quality and lung health is also weight dependent. In the SAPALDIA (Swiss Study on Air Pollution and Lung Disease in Adults) cohort, improvements in exposure to [PM.sub.10] (particulate matter with aerodynamic diameter [less than or equal to] 10 [micro]m) over an 11-year follow-up period were associated with attenuated age-related lung function decline. The association was strongest for the decline in forced expiratory flow at 25-75% ([FEF.sub.25-75]), an early marker of damage to the airways, but was also evident for [FEV.sub.1] and [FEV.sub.1]/FVC (Downs et al. 2007). We now investigate whether these previously reported attenuations were modified by BMI.

Methods

Study population. SAPALDIA is a population-based study of the long-term effect of air pollution on respiratory health in the Swiss adult population, as previously described in detail (Ackermann-Liebrich et al. …

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