Ontario Health Study

Many questionnaire variables have been collected at up to four timepoints. Click here to view a summary of all questionnaire data.

• Baseline questionnaire completed by about 225,000 participants.
• Almost 1,400 variables describing social and economic demographics, personal and family health histories, medications, sleep patterns, alcohol and tobacco use, physical activity and environmental exposures.

Ontario Health Study Baseline Questionnaire (PDF)

• Follow-up questionnaire completed in March 2018. It asked participants for an update on their health and additional questions around e-cigarettes and marijuana use, mental health and over-the-counter drugs. Data from the Follow-up Questionnaire are now available.

Ontario Health Study Follow-up Questionnaire (PDF)

• The Work History Questionnaire was completed in December, 2019. Data from the Work History Questionnaire are now available.
• Regular follow-up questionnaires will be conducted to track changes in overall health.

Ontario Health Study Work History Questionnaire (PDF)

• The COVID-19 Questionnaire was completed November 13, 2020. Data from the COVID-19 Questionnaire are now available.

Ontario Health Study and CanPath COVID-19 Questionnaire (PDF)

• The COVID-19 Antibody Study Questionnaire and the first of three blood spot sample collections was completed in June 2021. Data from this first timepoint are now available.

Ontario Health Study COVID-19 Antibody Questionnaire – Timepoint 1 (PDF)

Read the OHS Cohort Profile Paper in the International Journal of Epidemiology.

• Non-fasting blood samples were collected from more than 40,000 participants.
• The repository holds serum, plasma, red blood cells and buffy coat.
• For a subset of participants, (~6,000) there are lymphocytes in DMSO.
• ~9,400 samples have been genotyped using the UKBIObank Affymetrix arrays. Inflammatory markers have been assayed for a subset, including cytokine panels from 1,440 participants.
• Urine samples and physical measures were collected from 12,600 and 13,400 participants respectively.

Aliquot type and Volume

The number of aliquots and volume/amount available vary by aliquot type.

• Physical measures collected from ~13,400 participants include anthropometrics, standing and sitting height, blood pressure, resting heart rate, body fat percentage, grip strength and spirometry.

Physical measures and blood samples were collected through a variety of Study initiatives:

Regional assessment centres

Located in Mississauga, Owen Sound and Sudbury, men and women regardless of their health history were enrolled and invited to the nearest centre where they completed self- and interviewer-administered questionnaires, provided a number of physical measures and provided blood and urine samples. The assessment centres opened in 2009 and closed in July 2010. 

Toronto assessment centre

Starting in 2013, a subset of participants visited an assessment centre in downtown Toronto and provided a series of physical measures, blood and urine samples. This centre was closed March 2014.

Local study centres

The OHS hosted a series of temporary blood collection clinics in communities across the province. More than 50 clinics were held from summer 2014 until March 2017.

LifeLabs blood collection program

Through a partnership with LifeLabs Medical Laboratories, participants were able to provide samples at LifeLabs locations across Ontario. This program ran until March 2017.

Read the OHS Cohort Profile Paper in the International Journal of Epidemiology.

• The Ontario Sleep Health Study collects accelerometry and sleep respiratory function from approximately 4,000 participants.
• The Canadian Urban Environmental Health Research Consortium (CANUE) is working to provide researchers with an index measuring exposures to air and noise pollution, green space and much more, for every postal code in Canada. By providing this location-based exposure data to studies like the OHS and many others, CANUE will allow environmental exposure data to be linked to our participants, providing additional information and making our platform even more useful to health researchers.
• The Canadian Alliance for Healthy Hearts and Minds has collected MRIs, and conducted Food Frequency Questionnaires and cognitive assessments from more than 3,000 participants.
• A small study out of the University of Toronto (SPARK) asks 60 participants to wear contact lenses to explore new methods for the early detection of breast cancer.

Read the OHS Cohort Profile Paper in the International Journal of Epidemiology.

Changes in participant cancer diagnoses reported in our Follow-up Questionnaire

Of the more than 20,000 participant-reported cancer diagnoses, the most common cancers identified at follow-up are below.

Body Mass Index (kg/m²)

Hours of sleep per night

Age Distribution

Geographic Distribution by Public Health Unit

Read the OHS Cohort Profile Paper in the International Journal of Epidemiology.