The Ontario Health Study is a population-based study and active research platform investigating risk factors that cause diseases like cancer, diabetes, heart disease, asthma and Alzheimer's. More than 225,000 Ontario adults volunteered to be research participants, answering an online health-related questionnaire, and consenting to receiving subsequent surveys to follow their health as they age. A subset of participants also provided physical measurements and biological samples (41,000 blood samples and 12,600 urine samples).Researchers are using this long-term study to investigate how our lifestyle, environment and family history affect our health over time and to explore strategies for the prevention, early detection and treatment of diseases. The nonprofit Study is funded by the Ontario Institute for Cancer Research, Cancer Care Ontario, Public Health Ontario and the Canadian Partnership Against CancerThe Ontario Health Study is the largest of six study cohorts taking part in Canada's largest health research platform, the Canadian Partnership for Tomorrow's Health (CanPath).