Cardiovascular disease and air pollution in Scotland: no association or insufficient data and study design?
Lorna J Willocks
3
Abita Bhaskar
2
Colin N Ramsay
1
Duncan Lee
0
David H Brewster
5
Colin M Fischbacher
5
James Chalmers
5
George Morris
4
E Marian Scott
0
0
School of Mathematics and Statistics, University of Glasgow
,
Glasgow
,
UK
1
Health Protection Scotland
,
Glasgow
,
UK
2
MRC Social and Public Health Sciences Unit
,
Glasgow
,
UK
3
NHS Lothian
,
Edinburgh
,
UK
4
NHS Health Scotland
,
Glasgow
,
UK
5
Information Services Division, NHS National Services Scotland
,
Edinburgh
,
UK
Background: Coronary heart disease and stroke are leading causes of mortality and ill health in Scotland, and clear associations have been found in previous studies between air pollution and cardiovascular disease. This study aimed to use routinely available data to examine whether there is any evidence of an association between short-term exposure to particulate matter (measured as PM10, particles less than 10 micrograms per cubic metre) and hospital admissions due to cardiovascular disease, in the two largest cities in Scotland during the years 2000 to 2006. Methods: The study utilised an ecological time series design, and the analysis was based on overdispersed Poisson log-linear models. Results: No consistent associations were found between PM10 concentrations and cardiovascular hospital admissions in either of the cities studied, as all of the estimated relative risks were close to one, and all but one of the associated 95% confidence intervals contained the null risk of one. Conclusions: This study suggests that in small cities, where air quality is relatively good, then either PM10 concentrations have no effect on cardiovascular ill health, or that the routinely available data and the corresponding study design are not sufficient to detect an association.
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Background
The detrimental effects of air pollution on human health
came to public prominence in the mid 1900s, as a result
of high pollution episodes in the Meuse valley, Belgium
(1930), Donora, Pennsylvania (1948), and London, England
(1952). The latter was associated with more than 3,000
excess deaths [1], and was the catalyst for legislation such as
the UK Clean Air Act in 1956. Since then, a large number
of studies have investigated the health risks from air
pollution, and found consistent associations between
components of ambient air pollution and measures of ill health.
Numerous health endpoints have been considered in such
studies, with the most common being mortality [2] and
morbidity [3] from respiratory [4] and cardiovascular [5]
disease. A number of different pollutants have also been
considered in such studies, including, carbon monoxide
[6], ozone [7] and both coarse [8] and fine [3] particulate
matter. These studies have investigated the effects of both
long-term [9] and [10] and short-term [11] and [12]
pollution exposure, with the latter typically utilising an
ecological time series design. Such time series studies make
use of routinely available health and pollution data, and are
thus the most common study design because they are
inexpensive to conduct.
Studies such as those highlighted above provide evidence
for the creation of air pollution legislation and guidelines,
with examples in the UK being the Clean Air Act (1993)
and the Air Quality Strategy (2007). In recent times, the
conduit for such studies to effect UK legislation has been
the independent Committee On the Medical Effects of Air
Pollution (COMEAP), which informs governmental policy
by critiquing the evidence provided by such studies.
However, surprisingly few of these studies quantify the effects
of pollution in the UK, with the majority being based in
the USA [12] and [13], mainland Europe [11] and [14] or
Asia [15] and [16]. As a result, COMEAP has been forced
to base its recommendations to government on studies
from further afield, particularly the USA. The
transportation of evidence from one continent to another has its own
problems (as acknowledged by COMEAP), and suggests
that more studies are required to further assess the effects
of air pollution in the UK. Furthermore, the studies that
have been conducted in the UK have been predominantly
based in London [17] and [18], with relatively few assessing
the health impact of air pollution in Wales, Northern
Ireland or Scotland.
In Scotland, studies estimating the short-term effects
of pollution are limited to [19] and [20]. The short-term
study [19] was based in Edinburgh, and investigated the
effects of multiple pollutants, including nitrogen dioxide,
ozone and particulate matter, on multiple health
endpoints between 1981 and 1995. The results from this study
were largely negative, consistently showing no relationship
between pollution and ill health. Study [20] extended
study [19] to Aberdeen, Edinburgh and Glasgow, the three
largest cities in Scotland, and performed a meta-analysis
to give overall results for urban Scotland. Their study was
based on data from 1981 to 2001, and also failed to find
any consistent associations. (...truncated)