Cohort profile: The ONtario Population Health and Environment Cohort (ONPHEC)

Chronic diseases, including cardiovascular disease, diabetes mellitus, cancers and neurological disorders, constitute the most important global burden on disease, accounting for 68% of deaths and 54% of disability- adjusted life years (DALYs) each year. With increasing life expectancy, the impacts of chronic diseases will continue to rise. To reduce the substantial burden of chronic diseases, intervening on their major risk factors is the most cost-effective approach. Among various modifiable risk factors, environmental factors are increasingly being recognized as playing important roles in the development of a number of chronic diseases.

The World Health Organization (WHO) has estimated that approximately 24% of DALYs and 23% of deaths are attributable to five environmental risk factors: outdoor air pollution; indoor air pollution; exposure to lead; climate change; and lack of access to clean water, sanitation and hygiene. Environmental exposures may also yield beneficial effects on human health. For example, living in greener neighbourhoods may contribute to improvements in psychological well-being, increased physical activity and reduced obesity and overall mortality.

Many environmental risk factors, such as ambient air pollution and noise, are ubiquitous and can lead to large public health impacts. However, to quantify their health impacts, large cohorts are usually required, as the effect sizes of these exposures at the individual level are relatively small compared with risk factors such as tobacco smoking (for example, smoking increases the risk of lung cancer mortality by 15-fold). Recent advances in the volume and variety of electronic health records, and the rate at which they can be merged and analysed in the era of Big Data, provide an opportunity to create very large cohorts to acquire new insights into the environmental burden of chronic diseases.