Associations of Short-Term and Long-Term Exposure to Ambient Air Pollutants With Hypertension

Cardiovascular disease is the leading cause of death in the world. It is responsible for ≈30% of all deaths or ≈17.5 million people in 2012. As the major risk factor for cardiovascular disease, hypertension has been identified as the most important cause of disability and the leading risk factor for death globally and causes ≈16.5% of all deaths. The causes of hypertension are complex and are related to genetic factors, lifestyle, diet structure, and environmental factors, including air pollution. Since the 1990s, many epidemiological studies have investigated the associations between air pollution exposure and hypertension. However, the results remain controversial. Some studies have shown an association, whereas other studies have found either no association or an association only for selected pollutants or limitation based on short-term or long-term exposure. These inconsistent and controversial results indicate the need to quantitatively synthesize and interpret the available evidence to provide more explicit information for policy decisions and clinical use. Meta-analysis is the most commonly used statistical technique to quantitatively synthesize results from ≥2 separate studies. To our knowledge, there is only one meta-analysis that summarized the association between exposure to traffic-related air pollution and hypertension. However, this study included only cohort studies conducted in the Europe and mainly focused on the traffic-related air pollutants, which might limit the external validity of their findings. Therefore, more such meta-analyses are urgently needed. The previous published studies on hypertension and air pollution can be broadly divided into 2 categories: short-term and long-term studies. The former estimate the acute effects of air pollution exposure and mostly include time-series analyses over a few days. The latter evaluate the chronic effects of air pollution, such as cohort survival analyses over years of exposure. The short-term and long-term effects of air pollution may have Abstract—Hypertension is a major disease of burden worldwide. Previous studies have indicated that air pollution might be a risk factor for hypertension, but the results were controversial. To fill this gap, we performed a meta-analysis of epidemiological studies to investigate the associations of short-term and long-term exposure to ambient air pollutants with hypertension. We searched all of the studies published before September 1, 2015, on the associations of ozone (O 3 ), carbon monoxide (CO), nitrogen oxide (NO 2 and NO X ), sulfur dioxide (SO 2 ), and particulate matter (PM 10 and PM 2.5 ) with hypertension in the English electronic databases. A pooled odds ratio (OR) for hypertension in association with each 10 μg/m increase in air pollutant was calculated by a random-effects model (for studies with significant heterogeneity) or a fixed-effect model (for studies without significant heterogeneity). A total of 17 studies examining the effects of short-term (n=6) and long-term exposure (n=11) to air pollutants were identified. Short-term exposure to SO 2 (OR=1.046, 95% confidence interval [CI]: 1.012–1.081), PM 2.5 (OR=1.069, 95% CI: 1.003–1.141), and PM 10 (OR=1.024, 95% CI: 1.016–1.032) were significantly associated with hypertension. Long-term exposure (a 10 μg/m increase) to NO 2 (OR=1.034, 95% CI: 1.005–1.063) and PM 10 (OR=1.054, 95% CI: 1.036–1.072) had significant associations with hypertension. Exposure to other ambient air pollutants (short-term exposure to NO 2 , O 3 , and CO and long-term exposure to NO x , PM 2.5 , and SO 2 ) also had positive relationships with hypertension, but lacked statistical significance. Our results suggest that short-term or long-term exposure to some air pollutants may increase the risk of hypertension. (Hypertension. 2016;68:62-70. DOI: 10.1161/HYPERTENSIONAHA.116.07218.) • Online Data Supplement