The association of long-term exposure to PM2.5 on all-cause mortality in the Nurses' Health Study and the impact of measurement-error correction.
BACKGROUND
Long-term exposure to particulate matter less than 2.5 μm in diameter (PM2.5) has been consistently associated with risk of all-cause mortality. The methods used to assess exposure, such as area averages, nearest monitor values, land use regressions, and spatio-temporal models in these studies are subject to measurement error. However, to date, no study has attempted to incorporate adjustment for measurement error into a long-term study of the effects of air pollution on mortality.


METHODS
We followed 108,767 members of the Nurses' Health Study (NHS) 2000-2006 and identified all deaths. Biennial mailed questionnaires provided a detailed residential address history and updated information on potential confounders. Time-varying average PM2.5 in the previous 12-months was assigned based on residential address and was predicted from either spatio-temporal prediction models or as concentrations measured at the nearest USEPA monitor. Information on the relationships of personal exposure to PM2.5 of ambient origin with spatio-temporal predicted and nearest monitor PM2.5 was available from five previous validation studies. Time-varying Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95 percent confidence intervals (95%CI) for each 10 μg/m(3) increase in PM2.5. Risk-set regression calibration was used to adjust estimates for measurement error.


RESULTS
Increasing exposure to PM2.5 was associated with an increased risk of mortality, and results were similar regardless of the method chosen for exposure assessment. Specifically, the multivariable adjusted HRs for each 10 μg/m(3) increase in 12-month average PM2.5 from spatio-temporal prediction models were 1.13 (95%CI:1.05, 1.22) and 1.12 (95%CI:1.05, 1.21) for concentrations at the nearest EPA monitoring location. Adjustment for measurement error increased the magnitude of the HRs 4-10% and led to wider CIs (HR = 1.18; 95%CI: 1.02, 1.36 for each 10 μg/m(3) increase in PM2.5 from the spatio-temporal models and HR = 1.22; 95%CI: 1.02, 1.45 from the nearest monitor estimates).


CONCLUSIONS
These findings support the large body of literature on the adverse effects of PM2.5, and suggest that adjustment for measurement error be considered in future studies where possible.
Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 401 Park Drive, Landmark Center, Boston, MA, 02215, USA. Jaime.hart@channing.harvard.edu.|Department of Environmental Health, Harvard T.H. Chan School of Public Health, 401 Park Drive, Landmark Center, Boston, MA, 02215, USA. Jaime.hart@channing.harvard.edu.
Jaime E
JE
Hart
Department of Biostatistics, Harvard T. H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. stxia@channing.harvard.edu.|Department of Epidemiology, Harvard T.H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. stxia@channing.harvard.edu.
Xiaomei
X
Liao
Department of Epidemiology, Harvard T.H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. stbho@channing.harvard.edu.
Biling
B
Hong
Maryland Institute for Applied Environmental Health, University of Maryland School of Public Health, 2234 School of Public Health, College Park, MD, 20742, USA. rpuett@umd.edu.
Robin C
RC
Puett
Department of Public Health Sciences, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA, 17033, USA. JYanosky@phs.psu.edu.
Jeff D
JD
Yanosky
Department of Health Sciences, Bouve College of Health Sciences, Northeastern University, 360 Huntington Avenue, Boston, MA, 02115, USA. h.suh@neu.edu.
Helen
H
Suh
Department of Environmental Health, Harvard T.H. Chan School of Public Health, 401 Park Drive, Landmark Center, Boston, MA, 02215, USA. marianthi.anna@mail.harvard.edu.
Marianthi-Anna
MA
Kioumourtzoglou
Department of Biostatistics, Harvard T. H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. stdls@hsph.harvard.edu.|Department of Epidemiology, Harvard T.H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. stdls@hsph.harvard.edu.
Donna
D
Spiegelman
Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 401 Park Drive, Landmark Center, Boston, MA, 02215, USA. Francine.laden@channing.harvard.edu.|Department of Environmental Health, Harvard T.H. Chan School of Public Health, 401 Park Drive, Landmark Center, Boston, MA, 02215, USA. Francine.laden@channing.harvard.edu.|Department of Epidemiology, Harvard T.H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. Francine.laden@channing.harvard.edu.
Francine
F
Laden
D000328:Adult; D000397:Air Pollution / Q000009:adverse effects*; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D015994:Incidence; D009026:Mortality; D009726:Nurses; D010316:Particle Size; D052638:Particulate Matter / Q000009:adverse effects*; D011446:Prospective Studies; D014481:United States / Q000453:epidemiology
D052638:Particulate Matter