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The ONtario Population Health and Environment Cohort (ONPHEC) is a large population-based cohort of adult residents in the province of Ontario, Canada.

Ottawa, ON

The Cohort

The ONtario Population Health and Environment Cohort (ONPHEC) is a large population-based cohort of adult residents in the province of Ontario, Canada. It comprises virtually the entire population of Ontario who were aged 35 years or older from 1996 onwards, with continuous follow-up currently reaching 2016.

ONPHEC was created by linking multiple large-scale health administrative databases in Ontario, including hospitalizations, emergency department visits, physician office visits, prescription medications, and mortality, as well as population-based environmental databases, including air pollution, greenness, weather, and traffic-related noise. This unique “Big Data” provides a rich resource of information that can improve our understanding of the onset of chronic diseases in relation to environmental exposures.

  • Chronic disease tracked in the cohort include major cardiovascular diseases (hypertension, myocardial infarction, congestive heart failure, stroke, and atrial fibrillation), respiratory diseases (asthma and chronic obstructive pulmonary disease), diabetes mellitus, cancers (breast cancer and lung cancer), and neurodegenerative diseases (dementia, Parkinson’s disease, and multiple sclerosis).

  • Environmental exposures tracked include exposures to major air pollutants such as fine particulate matter (PM2.5), nitrogen dioxide (NO2), and ozone (O3); meteorological conditions such as air temperature and precipitation; traffic-related noise; and measures of green space such as the Normalized Difference Vegetation Index (NDVI). Environmental data has been assigned spatially to cohort members using their annual six-character postal codes during follow-up, which in urban areas, represent the centroid of the blocks or single large buildings in which they live.

  • Socio-demographic data have been linked at the individual level, including age, sex, immigrant status, and urban residency, and at the neighbourhood level, including family income, education, immigration, and unemployment.

  • Vital statistics including date and cause of death are available for the entire cohort.

  • Population-based health survey data has been used to link information on other individual-level risk factors for a representative sample of the cohort, including marital status, body mass index (BMI), education, smoking status, alcohol consumption, fruit and vegetable consumption, and physical activity.

Currently, ONPHEC has linked data across over 20 health administrative, chronic disease, and environmental databases, and as new data become available for these datasets, follow-up for ONPHEC will be further extended beyond 2018. Records were linked using unique, encoded identifiers, thereby protecting individual privacy. All data are held and linked at the Institute for Clinical Evaluative Sciences (ICES), located at Sunnybrook Health Sciences Centre in Toronto, Ontario.



The primary objectives of ONPHEC are to investigate the independent and combined effects of environmental stressors, such as air pollution and traffic-related noise, on the development and progression of chronic diseases, as well as their interactions with ‘healthy’ environmental factors such as green space.

Secondary objects of ONPHEC include:

  • Determining the effects of environmental exposures on the long-term survival of adults with select chronic diseases

  • Quantifying the burden of disease from adverse environmental factors

  • Evaluating the impacts of changes in environmental exposures on disease risk such as moving to less polluted neighbourhoods (or vice versa)

  • Identifying population subgroups who are most susceptible to the effects of environmental stressors, and who are disproportionately exposed

  • Evaluating public health impacts of environmental-related policies and programs



This cohort receives support from Public Health Ontario (PHO) and the Institute for Clinical Evaluative Sciences (ICES), which are funded by an annual grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). Various activities using this cohort were funded by grants from Health Canada and the Canadian Institutes of Health Research (CIHR).