Epidemiological time series studies of PM2.5 and daily mortality and hospital admissions: a systematic review and meta-analysis.
BACKGROUND
Short-term exposure to outdoor fine particulate matter (particles with a median aerodynamic diameter <2.5 μm (PM2.5)) air pollution has been associated with adverse health effects. Existing literature reviews have been limited in size and scope.


METHODS
We conducted a comprehensive, systematic review and meta-analysis of 110 peer-reviewed time series studies indexed in medical databases to May 2011 to assess the evidence for associations between PM2.5 and daily mortality and hospital admissions for a range of diseases and ages. We stratified our analyses by geographical region to determine the consistency of the evidence worldwide and investigated small study bias.


RESULTS
Based upon 23 estimates for all-cause mortality, a 10 µg/m(3) increment in PM2.5 was associated with a 1.04% (95% CI 0.52% to 1.56%) increase in the risk of death. Worldwide, there was substantial regional variation (0.25% to 2.08%). Associations for respiratory causes of death were larger than for cardiovascular causes, 1.51% (1.01% to 2.01%) vs 0.84% (0.41% to 1.28%). Positive associations with mortality for most other causes of death and for cardiovascular and respiratory hospital admissions were also observed. We found evidence for small study bias in single-city mortality studies and in multicity studies of cardiovascular disease.


CONCLUSIONS
The consistency of the evidence for adverse health effects of short-term exposure to PM2.5 across a range of important health outcomes and diseases supports policy measures to control PM2.5 concentrations. However, reasons for heterogeneity in effect estimates in different regions of the world require further investigation. Small study bias should also be considered in assessing and quantifying health risks from PM2.5.
Population Health Research Institute and MRC-PHE Centre for Environment and Health, St George's, University of London, London, UK.
R W
RW
Atkinson
Population Health Research Institute and MRC-PHE Centre for Environment and Health, St George's, University of London, London, UK.
S
S
Kang
Population Health Research Institute and MRC-PHE Centre for Environment and Health, St George's, University of London, London, UK MRC-PHE Centre for Environment and Health, King's College London, London, UK.
H R
HR
Anderson
Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Chilton, Oxfordshire, UK.
I C
IC
Mills
MRC-PHE Centre for Environment and Health, King's College London, London, UK NIHR Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London, London, UK.
H A
HA
Walton
D000393:Air Pollutants / Q000032:analysis / Q000633:toxicity*; D002318:Cardiovascular Diseases / Q000401:mortality; D004781:Environmental Exposure / Q000009:adverse effects* / Q000032:analysis; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008171:Lung Diseases / Q000401:mortality; D009026:Mortality / Q000639:trends*; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis / Q000633:toxicity*
D000393:Air Pollutants; D052638:Particulate Matter
Asthma Epidemiology; COPD epidemiology