Biology Reference
In-Depth Information
The auditory system, differing from the visual system, is permanently active also
during sleeping times, and even a low-level sound during the night can cause the
subject to awaken, creating, if this situation is repeated, fatigue and depression.
The effect of noise on sleep can be tested in the laboratory or in the field. The two
approaches have positive and negative elements, and integration between the two
approaches is required because large discrepancies have been found. People
exposed to heavy noise as in the proximity of an airport respond with sleep
disturbance, but when the noise dose is lower there are not evident differences
from the effects of road traffic noise.
If it is possible to insulate houses and sleeping rooms, reducing the effect of
noise on dwellers, the consequences of outdoor noise on sleep rhythms remain
obscure. People exposed during the day to heavy noise have difficulty sleeping.
Habituation to traffic noise reduces insomnia but is still connected to interindividual
variation in sensitivity to outdoor noise.
Prolongation of the awake state and shallow sleep reduces the useful time for
deep sleep and rapid eye movements (REM). Residents exposed to noise have
poorer sleep and at the morning show higher irritability. REM status decreases in
length according to increase of noise exposure.
Insomnia increases in inhabitants living close to busy highways, as has been
found in populations exposed to a traffic noise above 65
L
eq
dBA when compared
with inhabitants living in quieter areas. Physiological, psychological, and social
characteristics are further elements to be considered. Sleep disturbances become
evident when the subjects complain of difficulties falling asleep (delay) or of
awakening from sleep in the middle of the night or early morning.
The quality of noise makes the difference in evaluating the effect on people, so
intermittent noise has more adverse effects than a continuous noise level. Noise
peaks have more effects than the averaged weighted
L
eq
. Metabolic syndromes,
sleeping apnea, job stress, and shift work are all components that negatively affect
sleep performance, so noise exposure alone is not a sufficient factor to characterize
sleep disturbance (Kawada
2011
).
Health effects are expected in long-term periods that can create ischemic heart
disease and increased blood pressure. Epidemiologic studies on the relationship
between transportation noise and ischemic heart disease have demonstrated a
higher risk of myocardial infarction in subjects exposed to high levels of traffic
noise (Babisch et al.
2005
). An investigation carried out on 1,881 subjects aged
20-69 years affected by myocardial infarction (MI), compared with 2,234 controls,
has found the adjusted odds ratio for men exposed to sound levels of more than
70 dB(A) (adopting the acoustic map of the Berlin city). These results confirm the
hypothesis that people exposed to high levels of traffic noise are more at risk for
cardiovascular diseases than people living in quiet areas.
In conclusion, several studies have focused on the effect of noise on human
health, especially in the outdoor and indoor urban environment. Urban sounds are
not only noises but a complex communication system that affects in different ways
the human social network, well-being, and ultimately human health.
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