Recent studies have reported possible associations
between cardiovascular disease and both road traffic
noise
1
and road traffic air pollution.
2
Understanding
of the adverse effects of each pollutant on the
physiology of the cardiovascular system is incomplete; it is hypothesised that air pollution increases
blood pressure, contributes to the instability of
vascular plaques and may initiate cardiac arrhythmias,3
while the cardiovascular effects of noise are
hypothesised to be stress mediated via stimulation
of the hypothalamo-pituary-adrenal and sympathetic-adrenal-medullary axes. Chronic or repeated
stimulation of these axes leads to hypertension,
accumulation of intra-abdominal fat and insulin
resistance.
4
Because both exposures are strongly
associated with road traffic, and because of the
similarity in health endpoints, there is a possibility
that the two pollutants act jointly, or that traffic
noise may be a confounding factor in traffic-related
air pollution studies and vice versa.
To date, there have been limited attempts to
examine the combined effects of noise and air
pollution and these have used a variety of
approaches and outcomes. A recently published
study of road traffic noise and hypertension
investigated the joint effect by adjusting for PM10
levels in a noise–hypertension model. As this
adjustment did not alter the effect estimate of
noise on hypertension, the authors concluded that
the noise effect was independent but noted study
limitations including very small contrast between
high and low PM10levels.
5
An investigation of the
association between traffic noise and all-cause
cardiovascular and respiratory emergency hospital
admissions adjusting for air pollution (O3 and
NOx) found significant increases varying from
3.7% to 5.1% per decibel
6
; however, this study
had limited noise exposure data from only six
measurement stations across the city of Madrid.
Isinget alreported that traffic noise was associated
with aggravation of bronchitis in children, and that
this effect was more important than that of
exhaust fumes.
7
The two exposures were highly
correlated in their study, which unfortunately had
little power. A synergistic effect of traffic-related
noise and air pollution on levels of annoyance was
shown for a population in the city of Oslo.
8
Other
studies have raised the possibility of confounding,
but only data on traffic-related noise or on trafficrelated air pollution, but not both, were available.
910
Characterising the relationships between exposure to traffic-related noise and traffic-related air
pollution would aid the interpretation of previous
studies and contribute to the design of new
studies. Here we report the correlation between
noise and air pollution in a typical urban setting in
Vancouver, British Columbia