Long-Term Exposure to Traffic-Related Air Pollution Associated with Blood Pressure and Self-Reported Hypertension in a Danish Cohort

Article excerpt

BACKGROUND: Short-term exposure to air pollution has been associated with changes in blood pressure (BP) and emergency department visits for hypertension, but little is known about the effects of long-term exposure to traffic-related air pollution on BP and hypertension.

OBJECTIVES: We studied whether long-term exposure to air pollution is associated with BP and hypertension.

METHODS: In 1993-1997, 57,053 participants 50-64 years of age were enrolled in a population-based cohort study. Systolic and diastolic BP (SBP and DBP, respectively) were measured at enrollment. Self-reported incident hypertension during a mean follow-up of 5.3 years was assessed by questionnaire. We used a validated dispersion model to estimate residential long-term nitrogen oxides (NOx), a marker of traffic-related air pollution, for the 1- and 5-year periods prior to enrollment and before a diagnosis of hypertension. We conducted a cross-sectional analysis of associations between air pollution and BP at enrollment with linear regression, adjusting for traffic noise, measured short-term NOx, temperature, relative humidity, and potential lifestyle confounders (n = 44,436). We analyzed incident hypertension with Cox regression, adjusting for traffic noise and potential confounders.

RESULTS: A doubling of NOx exposure during 1- and 5-year periods preceding enrollment was associated with 0.53-mmHg decreases [95% confidence interval (CI): --0.88, --0.19 mmHg] and 0.50-mmHg decreases (95% CI: --0.84, -0.16 mmHg) in SBP, respectively. Long-term exposure also was associated with a lower prevalence of baseline self-reported hypertension (per doubling of 5-year mean NOx: odds ratio = 0.96; 95% CI: 0.91, 1.00), whereas long-term NOx exposure was not associated with incident self-reported hypertension during follow-up.

CONCLUSIONS: Long-term exposure to traffic-related air pollution was associated with a slightly lower prevalence of BP at baseline, but was not associated with incident hypertension.

KRY WORDS: air pollution, blood pressure, hypertension, epidemiology, nitrogen oxide. Environ Health Perspect 120:418-424 (2012). http://dx,doi.org/10.1289/ehp.1103631 [Online 3January 2012]

Exposure to particulate matter (PM) air pollution has been associated with myocardial infarction and stroke (Brook et al. 2010). The mechanisms believed to be involved include alteration of the autonomic function of the heart, vascular reactivity, induction of systemic inflammation, and endothelial dysfunction (Brook et al. 2010) which in turn may affect blood pressure (BP) and the risk of hypertension. It has therefore been hypothesized that high levels of air pollution may increase BP and the risk of hypertension.

Studies investigating associations between air pollution and BP have focused mainly on short-term effects, with some studies reporting small increases in systolic and diastolic BP (SBP and DBP, respectively) (Brook et al. 2009; Chuang et al. 2010; de Paula et al. 2005; Dvonch et al. 2009; Urch et al. 2005; Zanobetti et al. 2004) and others reporting no association (Madsen and Nafstad 2006) or even inverse associations (Brauer et al. 2001; Harrabi et al. 2006; Ibald-Mulli et al. 2004). Two studies have investigated associations between longer-term air pollution exposure and BP (Auchincloss et al. 2008; Chuang; et al. 2011). In a cross-sectional study of approximately 5,000 persons 45-84 years of age, Auchincloss et al. (2008) reported that the 30-day mean of PM2.5 (PM[less than or equal to] 2.5 [micro]m in aerodynamic diameter) was positively associated with SBP. whereas the association with DBP was weaker and statistically insignificant. In a cross-sectional study of 1,023 elderly persons, Chuang et al. (2011) reported that systolic and DBP both were highly correlated with yearly mean levels of several pollutants.

Little is known about the effects of air pollution on hypertension. Short-term exposure to air pollution has been positively associated with emergency department visits for hypertension (Guo et al. …