Associations of Short-Term and Long-Term Exposure to Ambient Air Pollutants With Hypertension
A Systematic Review and Meta-Analysis

Cai Y, Zhang B, Ke W, et al.
Hypertension. 2016;68: published online ahead of print

Background

Hypertension, a major risk factor for cardiovascular disease, is reported to be the leading risk factor for death, causing approximately 16.5% of all deaths worldwide [1]. Hypertension has been associated with genetic factors, unhealthy lifestyle, and environmental factors, including air pollution [2]. The study of the association between hypertension and air pollution has resulted in conflicting observations [3-5]. Inconsistency is partly due to study design, eg. short-term or long-term exposure. The short-term and long-term effects of air pollution may have direct and indirect effects on the sympathetic nervous system, oxidative stress, endothelial and other haemodynamic function, and vascular tone [6-9].
The hypothesis of this study was that the risk of hypertension increases, when there is an increase in ozone (O₃), carbon monoxide (CO), nitrogen oxide (NO₂ and NO_X), sulphur dioxide (SO₂) and particulate matter (PM₁₀ and PM_2.5). The aim of this meta-analysis was to systematically review the associations between air pollutants and risk of hypertension, as well as to quantify the short-term and long-term effects of ambient air pollutants on hypertension risk, by calculating a pooled odds ratio (OR) for hypertension in association with each 10 μg/m³ increase in air pollutant. Seventeen relevant studies were used for analyses

Main results

• The risk of hypertension was significantly associated with short-term exposure to SO₂ (OR: 1.046; 95% CI: 1.012–1.081), PM_2.5 (OR: 1.069; 95% CI: 1.003–1.141) and PM₁₀ (OR: 1.024; 95% CI: 1.017–1.030).
• Hypertension was marginally statistically significantly associated with short-term exposure to NO₂ (OR: 1.037; 95% CI: 0.994–1.082).  

• There was a statistically significant increase in hypertension risk in association with each 10 μg/m³ increment in long-term exposure to NO₂ (OR: 1.034; 95% CI: 1.005–1.063) and PM₁₀ (OR: 1.054; 95% CI: 1.036–1.072).

• Non-significant associations of hypertension risk with long-term exposure to NO_x (OR: 1.127; 95% CI: 0.933–1.361) and PM_2.5 (OR: 1.065; 95% CI: 0.985–1.152) and SO₂ (OR: 1.732; 95% CI: 1.309–2.308 according to Chan et al and OR: 1.054; 95% CI: 1.020–1.086 according to Dong et al) were seen.

Conclusion

In a systematic review and meta-analysis of 17 studies, the short-term and long-term exposure to air pollutants was significantly associated with increased risk of hypertension. More specifically, these effects were seen with short-term SO₂, PM_2.5 and PM₁₀ and long-term NO₂ and PM₁₀.

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