Hypertension and Exposure to Noise near Airports

Abstract and Introduction

An increasing number of people live near airports with considerable noise and air pollution. The Hypertension and Exposure to Noise near Airports (HYENA) project aims to assess the impact of airport-related noise exposure on blood pressure (BP) and cardiovascular disease using a cross-sectional study design. We selected 6,000 persons (45-70 years of age) who had lived at least 5 years near one of six major European airports. We used modeled aircraft noise contours, aiming to maximize exposure contrast. Automated BP instruments are used to reduce observer error. We designed a standardized questionnaire to collect data on annoyance, noise disturbance, and major confounders. Cortisol in saliva was collected in a subsample of the study population (n = 500) stratified by noise exposure level. To investigate short-term noise effects on BP and possible effects on nighttime BP dipping, we measured 24-hr BP and assessed continuous night noise in another subsample (n = 200). To ensure comparability between countries, we used common noise models to assess individual noise exposure, with a resolution of 1 dB(A). Modifiers of individual exposure, such as the orientation of living and bedroom toward roads, window-opening habits, and sound insulation, were assessed by the questionnaire. For four airports, we estimated exposure to air pollution to explore modifying effects of air pollution on cardiovascular disease. The project assesses exposure to traffic-related air pollutants, primarily using data from another project funded by the European Union (APMoSPHERE, Air Pollution Modelling for Support to Policy on Health and Environmental Risks in Europe).

An increasing number of people live in the vicinity of major airports and experience considerable noise and air pollution. Raised blood pressure (BP) is a major risk factor for coronary heart disease and the major risk factor for stroke (Whitworth 2003). Environmental noise is a significant problem in Europe, and it is estimated that roughly 20% of the European Union's population (close to 80 million people) are exposed to noise levels that are considered unacceptable (European Commission 1996).

Few investigators have studied health effects associated with exposure to aircraft noise. Cardiovascular effects due to noise exposure have been studied to some extent, but no clear exposure-response relations are currently known (Babisch 2000), although a recent German study showed an excess risk of myocardial infarction related to traffic noise, but only in men (Babisch et al. 2005). An early European study showed higher treatment rates for "heart trouble" and hypertension among residents close to a major airport than among people living farther away (Knipschild 1977), and a later review found that hypertension was more prevalent among individuals living close to airports (Vacheron 1992). However, results are equivocal both with respect to BP increases (Babisch et al. 1990; Lercher et al. 2000; Pulles et al. 1990) and the prevalence of hypertension (Bluhm et al. 2001; Eiff and Neus 1980; Herbold et al. 1989; Knipschild and Sallé 1979; Maschke 2003). A recent cross-sectional study indicated an exposure-response relation between residence distance from a Swedish airport and hypertension (Rosenlund et al. 2001). Similar results were found in a community sample around a military airbase on Okinawa, Japan, and in a cross-sectional survey around Schiphol airport in Amsterdam, the Netherlands (Franssen et al. 2004; Matsui et al. 2004).

In 1999, the World Health Organization stated that the overall evidence available at the time suggested a weak association between long-term noise exposure and BP elevation or hypertension, and that cardiovascular effects are associated with long-term exposure to A-weighted average sound pressure levels [dB(A)] (L _Aeq,24hr) throughout the day/night in the range of 65-70 dB(A) (Berglund et al. 1999). However, a recent German study suggested that traffic noise at lower levels might increase the risk of myocardial infarction and high BP, finding an increased odds ratio for medical treatment of hypertension in subjects with an exposure during the day/night of > 60/50 dB(A) compared with subjects with an exposure < 60/50 dB(A) (Maschke 2003). Recent studies suggest that nighttime exposure might be particularly relevant for health (Babisch et al. 1999; Health Council of the Netherlands 2004; Lercher and Kofler 1993; Maschke 2003).

Stress hormones are useful indicators to study mechanisms and interactions between noise and health outcomes such as BP (Babisch et al. 2001). The cortisol level is a good indicator of stress (Wust et al. 2000). Salivary cortisol correlates well with free levels of cortisol in serum, and correctly collected saliva samples have the advantage of being stable for long periods at room temperature (Hofman 2001), which facilitates their use in multicenter studies.

Community noise studies have traditionally considered only noise from a single specific source such as aircraft or road traffic. However, recent studies suggest that aircraft noise might be more annoying than road traffic noise (Miedema and Oudshoorn 2001), but the extent to which the findings from individual studies can be extrapolated to other environments is at present unclear. It is not meaningful to use a total integrated estimate of noise in studies of nonauditory effects, because sound energy is not the only factor that causes stress reactions. Attitudes toward noise and the activities disturbed by it may modify the effect of noise quite considerably, as well as objective characteristics such as time pattern and sound frequency distribution. However, in studies of effects of community noise, nuisance from other noise sources should be addressed as independent (or interacting) factors (as is commonly done in environmental epidemiologic studies) (Babisch 2002; Babisch et al. 2003; Pulles et al. 1990).

The literature relating hypertension to air pollution is sparse, and two recently published studies show contradictory results (Ibald-Mulli et al. 2004; Zanobetti et al. 2004), but there is a wealth of literature on air-pollution-related cardiovascular effects, particularly associated with short-term changes in particulate air pollution levels (Dockery 2001). A recent study showed increased cardiopulmonary mortality associated with living near major roads (Hoek et al. 2002). However, although mortality was associated with living near roads, there was less consistency in the relation with ambient air pollution concentrations. In spite of this, no attempts were made to adjust for road-traffic-related noise. Thus, it may be important to assess ambient air pollution exposure as a possible confounder/effect modifier of the association between community noise and cardiovascular risk.

The aim of the Hypertension and Exposure to Noise near Airports (HYENA) project is to assess the impacts on cardiovascular health (primarily reflected by high BP) of noise generated by aircraft and road traffic near six major European airports (Athens, Greece; Milano/Malpensa, Italy; Amsterdam/Schiphol, the Netherlands; Stockholm/Arlanda, Sweden; Berlin/Tegel, Germany; and London/Heathrow, UK). The project will identify and quantify noise exposure in individuals, relating exposure to prevalence of high BP.

The project will study a subsample of subjects in more detail, recording 24-hr BP (every 15 min) and continuous night noise measurements, to assess the short-term effects of aircraft noise during nighttime and its effects on BP nighttime dipping, which is an established risk factor for cardiovascular disease (Lee et al. 2005; Ohkubo et al. 2002).

The project will evaluate the modifying effects of traffic-related air pollution [nitrogen dioxide, particulate matter with aerodynamic diameter ≤ 10 µm (PM₁₀)] on noise-associated cardiovascular risk factors and cardiovascular disease (high BP, ischemic heart disease). Standardized methods for assessing exposure and effect are used, and exposure-response relationships between environmental noise exposure and health outcomes will be calculated. The project will analyze acute BP changes related to short-term aircraft noise exposure (nighttime in particular).

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