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Swedish retrospective cohort on
air pollution – feasibility study.
There is now wide consensus that
the risk assessment of air pollution effects on mortality should be based on
long-term studies. There are however only three such studies available, all from
North America. A pooled risk estimate has been calculated to an increased
age-specific risk of dying by 6% for a long-term increase of air pollution by 10
µg/m³ PM2.5. There is a great need of further studies, preferably
from other regions and in lower ranges of air pollution.
The emission databases that are
being constructed in Swedish metropolitan areas offer unique possibilities of
retrospective exposure assessment for the general population, based on
dispersion modelling. Such exposure assessment has already shown to be useful in
a case-control study of lung cancer in Stockholm. A similar effort for Scania is
described elsewhere in this program. Not only may air pollution mapped with
great detail, but different categories of sources may be evaluated separately.
The previous cohort studies
incorporated 6 000 – 300 000 subjects aged 30+, and 8 - 18 years of follow-up,
resulted in 1 400 – 21 000 deaths. The exposure range was
approximately 10 – 30 µg/m³ PM2.5. A recent re-analysis of two of
the studies has largely confirmed the original observation, with the addition of
a substantial modifying effect from education.
Before constructing a new large
cohort in Sweden for these purposes, a number of outstanding questions need to
be addressed, e.g.:
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In which Swedish metropolitan
areas can retrospective exposure assessment be made with sufficient spatial
detail?
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What are the anticipated
exposure contrasts in these areas?
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What background information
can be easily obtained for the cohort members, for control of effect
modification and confounding?
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Based on these considerations,
how large a cohort is necessary to improve the knowledge base?
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To what extent may existing
cohorts be used?
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Is it possible to create
similar cohorts in the other Nordic countries?
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How can such a large study be
organised and financed?
The final result of this study
would be a judgement of the practical and financial feasibility, and – if both
positive - a study protocol and preliminary plan for financing. Since the
enlargement of the knowledgebase is important not only for health impact
assessment in Sweden, it is anticipated that international economic support may
become available.
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