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Environmental Noise and Health
One of the most important documents to emerge outlining the noise-health relationship in recent years has been Bur- den of Disease from Environmental Noise produced by the European arm of the World Health Organization (WHO; 2011). The document represents the first serious attempt anywhere in the world to examine the evidence base for the noise-health relationship. But it also goes further and produces estimates (for which there is sufficient evidence) of the extent of the disease burden. The calculations utilize data taken from strategic noise maps produced as part of EU member state requirements under the terms of the En- vironmental Noise Directive (END) that will be discussed briefly in the following section. The WHO (2011) express- es the burden of disease in terms of disability-adjusted life years (DALYs), which is the sum of potential years of life lost due to ill health, disability, or early death and the equiva- lent years of healthy life lost due to being in a state of poor health or disability (Murphy and King, 2014). Put another way, one DALY is equivalent to an individual losing one year of healthy life.
Table 1 highlights the extent of DALYs lost due to environ- mental noise exposure in Europe. The main impacts are in terms of annoyance and sleep disturbance, but both are re- lated to other impairments in both adults and children. The five noise-induced exposure impacts referred to cumulative- ly result in the loss of approximately 805,300 DALYs annu- ally. The WHO study concludes that one in three individuals in Europe is annoyed during the daytime and one in five has disturbed sleep at night purely from traffic noise alone. In cities around the world, it is typically the various forms of transportation that are the main source of environmental noise exposure, with road transport, in particular, being the main offender. In the United States, similar estimates have not been undertaken. However, as far back as 1981, the US Environmental Protection Agency estimated that almost 100 million people in the United States had annual exposure levels to environmental noise that were harmful to human health (Simpson and Bruce, 1981). Despite this, Hammer et al. (2014) note that the US Congress has not seriously dis- cussed environmental noise in more than 30 years. In addi- tion, the recent US study by Swinburn et al. (2015) suggests that reducing environmental noise by a 5-dB A-weighted day-night equivalent level (LDN; the sound level measured over a 24-hour period, with a 10-dB penalty added to the level between 2300 and 0700 hours) would reduce hyperten-
sion cases by 1.2 million (1.4%) and chronic heart disease cases by 279,000 (1.8%). Moreover, they estimate the annual associated cost savings and productivity gains in the region of USD 3.9 billion.
Table 1. Annual burden of disease from environmental noise in Europe
DALYs, disability-adjusted life years; EUR-A, World Health Organization(WHO) epidemiological subregion in Europe comprising Andora, Austria, Belgium, Croatia, Cyprus, the Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Israel, Italy, Luxembourg, Malta, Monaco, The Netherlands, Norway, Portugal, San Marino, Slovenia, Spain, Sweden, Switzerland, and the United Kingdom. Tinnitus is defined as the sensation of sound in the absence of an external sound source (WHO, 2011). Adapted from WHO (2011).
The noise-stress relationship is well understood in princi- ple. Noise activates the sympathetic and endocrine system (Babisch, 2002). Changes in the level of stress hormones are often found in acute and chronic noise experiments: researchers have found increases in the release of stress hormones including catecholamines, adrenaline and nor- adrenaline, and the corticosteroid cortisol (Babisch, 2003). Moreover, results from laboratory studies have found chang- es in blood flow, blood pressure, and heart rate in reaction to noise stimuli.
Two principal pathways are outlined in the literature that relate noise exposure to negative health effects (Babisch, 2002). These are the “direct” and “indirect” arousal and ac- tivation of the human organism. Direct arousal results from the instantaneous interaction of the acoustic nerve (eighth cranial nerve) with structures of the central nervous system.
However, it is the indirect pathway that is more relevant, and indeed important, for environmental noise exposure. The indirect pathway refers to the cognitive perception of sound, its cortical activation, and related emotional re- sponses whereby both the noise level and the subjective ef- fects of noise annoyance are associated with negative health impacts (Babisch et al., 2013; Murphy and King, 2014). The indirect pathway begins with noise-induced disturbances of activities such as communication or sleep. Indeed, noise induces stress not only by disturbing sleep but also by in- terfering with relaxation and concentration (and other cog- nitive functions). The resultant stress activates the sympa- thetic nervous system and the endocrine system (Babisch et al., 2001). In the laboratory, physiological experiments on
Table 1. Annual burden of disease from environmental noise in Europe
Noise-Induced Exposure
    Public Health Impact
      587,000 DALYs lost for inhabitants in towns >50,000 population
     Sleep disturbance
    90,3000 DALYs for EUR-A inhabitants in towns >50,000 population
   Cardiovascular diseases
  61,000 years for ischemic heart disease in high-income European countries
    22,000 DALYs for the EUR-A adult population
   Cognitive impairment in children
      45,000 DALYs for EUR-A countries for children aged 7-19 years
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