Long-term exposure to ambient PM2.5 associated with fall-related injury in six low- and middle-income countries☆
Graphical abstract
Introduction
As one leading cause of hospitalization and premature mortality, falls accounted for about four fifths of the disability associated with unintentional injuries excluding traffic accidents among adults aged 50 years and above in 2010 (Rubenstein, 2006, Williams et al., 2015a). Falls remain an important public health problem among older adults in both developed and developing countries, particularly within countries with large aging populations (Williams et al., 2015b).
More than 70% of the older population in the world is estimated to reside in low- and middle-income countries, and this fraction is expected to increase in the coming years (Beard et al., 2012). This shift will likely result in a greater disease burden of falls in these countries (Williams et al., 2015a). For instance, in 2010, the prevalence of falls related to years lived with disability (YLDs) was 631 and 674 per 100,000 population in India and China, respectively; while the corresponding rate was 472 per 100,000 in the United States (Wang et al., 2008, Williams et al., 2015a). More studies are thus warranted to identify risk factors, especially those that are understudied and preventable, and can be targeted by appropriate policies and intervention approaches in order to reduce the risk of falls in these aging populations.
Exposure to ambient air pollution has been associated with a great body of adverse health outcomes, including cardiovascular and respiratory morbidity and mortality (Bentayeb et al., 2015, Halonen et al., 2015, Lin et al., 2017a), age-related cognitive decline (Lertxundi et al., 2015), rheumatoid arthritis (Hart et al., 2013), and disability (Lin et al., 2017c). Given that fall-related injury is a consequence of these subclinical processes and chronic diseases (Masud and Morris, 2001), it is reasonable to hypothesize that exposure to air pollution may also influence the likelihood of suffering a fall-related injury among older populations. It is possible that exposure to ambient air pollution could directly and indirectly affect risk of fall-related injury. High levels of air pollution, especially fine particulate matter pollution (PM2.5), could directly increase the possibility of falls due to the reduced visibility (Tao et al., 2017). Recent studies have linked air pollution exposure with the pathophysiologic processes contributing to various health outcomes, such as hypertension, stroke, systemic inflammation, etc (Honda et al., 2017, Lin et al., 2017b, Scheers et al., 2015), some of these health conditions have been linked with increased risk of falls, especially among older adults (Bergland and Wyller, 2004, Harris et al., 2005).
While a series of studies have explored the health effects of long-term exposure to ambient PM2.5 (particles with an aerodynamic diameter ≤2.5 μm), fewer have studied the potential effect modification by dietary factors (such as consumption of fruit and vegetables), which might serve as an intervention strategy to mitigate the adverse health effects of PM2.5 (Villarreal-Calderon et al., 2010). Fruit and vegetables are the primary dietary source of antioxidants in our daily life (Balsano and Alisi, 2009). Previous studies have suggested that oxidant stress is one important biological pathway of the health effects of PM2.5 exposure (Kelly, 2003). Higher intake of antioxidant nutrients have been found to be important effect modifiers for air pollution health effects (Romieu et al., 2008, Villarreal-Calderon et al., 2010). We thus hypothesize that higher consumptions of fruit and vegetables may potentially counter the adverse health effects of ambient PM2.5.
Furthermore, it is important to estimate the disease burden attributable to ambient PM2.5 exposure, findings from such analyses would shed light on the better understanding of the public health significance of ambient PM2.5 exposure (Lin et al., 2017b).
The present study was therefore conducted to examine the association between ambient PM2.5and fall-related injury among people aged ≥50 years. We also investigated whether the consumption of fruit and vegetables could modify the association. To provided more insights on the disease burden of PM2.5, we further estimated the burden of fall-related injury attributable to ambient PM2.5.
Section snippets
Study participants
We used the baseline survey data from the World Health Organization's Study on Global AGEing and Adult Health (SAGE). Details on the study design and data collection have been reported elsewhere (Kowal et al., 2012). Briefly, SAGE is an on-going longitudinal cohort study with nationally representative adults population in the six low- and middle-income countries: China, Ghana, India, Mexico, the Russian Federation, and South Africa. The data were collected using validated instruments derived
Results
A total of 40,583 participants aged 50 years and older were initially invited to participate in the survey, among which, 36,742 agreed to participate in this survey, giving a response rate of 90.5%. Among them, 80 had missing values for age, sex or other important covariates, the remaining 36,662 participants were included in this analysis. Characteristics of the 36,662 participants are presented by country in Table 1. The three-year averaged PM2.5 concentration in the six countries was
Discussion
This study observed a significant association between long-term exposure to ambient PM2.5 and fall-related injuries in six low- and middle-income countries. Our hypothesis that higher consumption of fruit and vegetables may alleviate this association was supported. We further estimated that about 7% of the fall-related injuries could be attributable to ambient PM2.5 in the study population. To our knowledge, this is the first study to report such an association and its effect modification and
Conclusions
Our study suggests that ambient PM2.5 may be one important risk factor for fall-related injury, and is responsible for substantial related disease burden, and that higher consumption of fruit and vegetables could alleviate this effect.
Funding
The authors thank the respondents and survey teams from the six SAGE countries.
This study was partially supported by the US National Institute on Aging through Interagency Agreements (OGHA 04034785; YA1323-08-CN-0020; Y1-AG-1005-01) and through a research grant (R01-AG034479). Three-year Action Plan on Public Health, Phase IV, Shanghai, China (15GWZK0801) (GWIV-22).
Conflicts of interest
The authors have no conflict of interests to declare.
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This paper has been recommended for acceptance by Dr. Chen Da.
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These authors contributed equally to this work.