3.3: Actual Effects of Noise on Health
A considerable amount of research has been carried out to attempt to relate noise dose to the various potential or hypothesised effects. Much of this work has merely looked for statistical associations between indicators of noise exposure and indicators of noise effect, but of course, statistical association on its own does not in any sense 'prove' cause and effect. The main problem here is that, if there are any real effects of environmental noise on health (other than 'simple' effects such as annoyance, sleep disturbance, and interference with speech and task performance), then they are likely to be quite complex and associated with more than one 'causal' factor. For example, since it is well known that different individuals respond differently to various kinds of stress, then there are likely to be a whole range of individual differences in terms of health effects of noise, very few of which can ever hope to be properly controlled in any feasible research study design. Potential confounding factors and co-related variables include genetic pre-dispositions to particular health effects, individual diet and lifestyle, adopted coping strategies (the extent to which individuals might have adapted their lifestyle to accommodate otherwise unacceptable environmental stress), and various possible self-selection biases. It is possible that, on average, people who are long term resident in higher environmental noise areas might be somehow different from people who are long term resident in quieter areas as a result of having different priorities when making employment and housing choices over many years. Cross-sectional epidemiological studies cannot be expected to be able to unravel all these possible relationships, some of which might even be hypothesised to operate in different directions depending on the other circumstances present. Longitudinal studies are in theory capable of controlling for individual differences to a much greater extent, but outcomes will still depend on how patterns of noise exposure change over several years in relation to other social, economic and political changes that might occur.
On the other hand, just because research has not definitely 'proved' any causal linkage between environmental noise and long term adverse health effects, this does not mean that such linkages do not exist. It remains inherently plausible that excessive noise might contribute to long term adverse health effects, and because of this the whole area is increasingly becoming a matter of public concern.
Table 2 summarises the findings of two previous review articles, in terms of the perceived strength of available evidence in support of particular noise and health linkages. Of course, each of these findings merely represent the consensus view of the different panels of experts available at the time and are subject to modification and change as new research results become available in the future. The main findings of the primary research have shown that the following conclusions can be made about the actual existence of effects of noise on health:
- Environmental noise exposure definitely leads to reported noise annoyance in representative populations.
- Reported noise annoyance increases with noise exposure.
- Reported noise annoyance varies in different situations and in different contexts.
- Environmental noise causes other effects such as speech interference, performance interference and sleep disturbance. These effects vary depending on situation and context.
- Although speech interference can be explained by direct background noise masking, the extent to which any particular degree of speech interference can be overcome or contributes to stress in different situations is less clear.
- Sleep disturbance caused by noise is a real phenomenon, but there is considerable evidence that residents can habituate to noise and there is some doubt as to the real long term consequences of any particular degree of noise induced disturbance. It is unclear how much sleep loss is actually required before being considered a health effect but excessive interference with sleep does seem to compromise positive mental well-being.
- There is some weak evidence that environmental noise exposure may contribute to non-auditory health effects such as cardio-vascular disease.
- The evidence for real effects contributing to increased morbidity such as cardiovascular effects is not convincing at this time, although it seems scientifically plausible that a minority of the population exposed at the highest noise levels might be susceptible to some increased risk.
- Much of the evidence in support of these non-auditory health effects is based on extrapolation from laboratory studies of occupational exposure at much higher noise levels. Such extrapolation is not necessarily valid.
- There is less convincing evidence of non-auditory health effects based on direct field studies of environmental noise exposure. It is possible that such effects exist but might be very difficult to detect statistically. There are serious methodological difficulties involved in being able to carry out definitive research.
- The available literature on this topic is contradictory. In general, it is only the most poorly designed and executed results which show significant effects. Significant effects amongst the most susceptible members of the population could remain scientifically plausible, even if they are as yet unproven.
Table 2: Strength of evidence for a particular effect as judged in earlier reviews
Effect Strength of evidence Annoyance Sufficient*1 Sufficient*2 Sufficient*5 Psychiatric disorders Inconclusive*1 Limited*2 Inconclusive*3 Inconclusive*5 Weak*6 Suggestive but inconsistent*7 Performance Limited*2 Task dependent*5 performance by school Sufficient*1 Sufficient*2 children Sleep changes to sleep pattern Sufficient*2 Sufficient*7 onset/latency Sufficient*1 waking during the night Sufficient*1 Sufficient*2 waking prematurely in the Sufficient*1 Sufficient*3 morning changes to sleep stages Sufficient*2 sleep loss Sufficient*7 subjective reports of Sufficient*1 Sufficient*2 Sufficient*3 sleep quality mood next day Sufficient*1 Sufficient*2 sleepiness and performance Inconclusive*1 Limited*2 next day heart rate Sufficient*2 hormones Limited*2 immune system Inadequate*2 Hearing loss Sufficient*2 Sufficient*5 Stress related health effects hypertension Inconclusive*1 Sufficient*2 Inconclusive*3 ischaemic heart disease Sufficient*1 Sufficient*2 forms of cardiovascular Inconclusive*3 Inconclusive*5 Limited*6 disease biochemical effects Limited*2 immune effects Limited*2 Inconclusive*6 birthweight Inconclusive*1 Limited*2 Inconclusive*3 Inconclusive*7 congenital Lack*2 Inadequate*5
Key: source and classifications:
*1 (IEH 97),
sufficient : sufficient evidence for a causal association between noise exposure and the health end point
inconclusive: evidence for a causal link between noise exposure and the health end point is inconclusive
*2 (NETHERLANDS 97)
Sufficient: a relationship has been observed between noise exposure and a specific health effect, chance, bias and confounding factors can be ruled out with reasonable confidence
Limited: an association has been observed between noise exposure and a specific health effect, chance, bias and confounding factors cannot be ruled out with reasonable confidence
Inadequate: the available studies are of insufficient quality, lack the consistency or statistical power to permit a conclusion regarding the presence of absence of a causal relationship
Lack: several adequate studies are mutually consistent in not showing a positive association between exposure and health effect
*3(MORREL 97) *4 (BERGLUND 96) *5(SHAW 96) *6(THOMPSON 97) *7(JOB 96)
Classifications inferred from text
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Published 12 September 2000
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