Night noise guidelines for Europe - WHO/Europe - World Health ...

100 EFFECTS ON HEALTH
Furthermore, there are potential instantaneous effects, such as effects on memory
consolidation or restoration of the immune system, for which the information
on a possible relation with noise exposure is so limited that they were not considered
here. In order to acquire more insight into these effects, more field
research is needed. Field research is needed because earlier studies have shown
that estimates of effects on the basis of laboratory studies are much higher than
estimates from field studies. Methodological differences between the different
approaches certainly cannot be the only possible explanation. Research allowing
the introduction of some specific but light laboratory technique into the sleeper’s
own bedroom, should be encouraged, as, for example, used in the Swiss Noise
Study 2000 (Brink, Müller, and Schierz, 2006). The key to better insight into
effects of night-time noise, leading to mechanistic models describing the relationships
between noise exposure, instantaneous effects, effects at the level of a 24-
hour period and chronic effects, appears to be epidemiological studies at home
with well-designed instrumentation.
The relationships between noise exposure, instantaneous effects, effects at the
level of a single 24-hour period and chronic effects is complex because the effects
at a smaller time scale do not simply add up to effects at a larger time scale. For
example, the noise-related increase in night-time average motility was substantially
higher than would be expected on the basis of the instantaneous extra
motility at the times of the noise events (Passchier-Vermeer et al., 2002), suggesting
persistent arousal during sleep related to aircraft noise. It is likely that such
shifts in the basic state are more important for the development of chronic effects
than the instantaneous effects per se. A further complication is that some effects
habituate. Habituation in some effect parameters can occur in a few days or
weeks, but the habituation is not always complete. The measured modifications
of the cardiovascular functions remain unchanged over long periods of exposure
time (Muzet and Ehrhart, 1980; Vallet et al., 1983). Most striking is that none of
the cardiovascular responses show habituation to noise after a prolonged exposure,
while subjective habituation occurs within a few days. It appears plausible
that, in particular non-habituating effects lead to the development of chronic
effects, but also the disappearance of effects with continuing exposure may come
at a cost associated with suppressing the effects. A third complication is that daytime
noise exposure may contribute to the effects found in relation to night-time
noise. Large epidemiological studies are needed that compare populations
exposed to similar daytime noise and differ in their night-time noise exposure
only. A specific challenge for mechanistic models on the effects of noise on sleep
is the identification of factors that make subjects vulnerable to night-time noise.
The following groups may be hypothesized to be more vulnerable to noise during
sleep: old people, ill people, people with chronic insomnia, shift workers and people
resting during daytime, people with a tendency to depression, light sleepers,
pregnant women, people with high anxiety and high stress levels. Furthermore,
children need attention because of their relatively high exposure during sleep, and
because they are in a phase of neurocognitive development for which undisturbed
sleep may be particularly important.
NIGHT NOISE GUIDELINES FOR EUROPE