Cohort Profile: The Ontario Health Study (OHS)

The Ontario Health Study (OHS) is a resource for investigating the ways in which lifestyle, the environment and genetics affect people’s health. It is one of the regional cohorts that collectively form the Canadian Partnership for Tomorrow’s Health (CanPath)—a pan-Canadian cohort with >330 000 participants. The linking of Canada’s rich collection of administrative health data with the cohort’s data represents a powerful means to disseminate high-quality, timely data. From 2009 to 2017, the OHS recruited participants from the general population of Ontario through targeted recruitment strategies. Adult residents of Ontario aged ≥18 years were eligible for inclusion; the mean age at recruitment was 46 years (range: 18–97 years). A total of 225 620 people (137 918 female, 87 702 male) comprise the OHS baseline cohort. At study entry, cohort members completed a questionnaire that collected information on socio-demographics, family history, health status, behavioural factors, lifestyle factors and self-reported anthropometry. A subset of participants provided blood samples and physical measures. A follow-up questionnaire was administered from 2016 to 2019, a work-history questionnaire in 2019, and COVID-19 questionnaires and dried blood spots were collected from 2020 to 2022. Biologic samples have supported genotyping and whole-genome sequencing, and repeat blood spots have supported COVID-19 serology studies. Participants are followed actively through questionnaires and passively via linked environmental and administrative health data. Data and biosamples are available to researchers through a data and sample access process (e-mail: [email protected]). The prevalences of many chronic diseases—including cancer, cardiovascular disease, asthma and type 2 diabetes—have increased in Canada and many other countries over the past 30 years.1–4 In 2020, cancer and heart disease were the leading causes of death for Canadians, accounting for 48% of all deaths.5 About 37% of seniors (aged ≥65 years) have at least two common chronic diseases, with almost 50% of seniors aged ≥85 years suffering from multimorbidity.6 Chronic diseases are associated with high healthcare costs,7 rising complexity of care, long-term morbidity and mortality,8 and as such are major public health problems both in Canada and the rest of the world. A better understanding of their natural histories and complex and interrelated causes is needed to bring about the promise of disease prevention and early detection. Established to facilitate prospective observational health research, the Ontario Health Study (OHS; OntarioHealthStudy.ca) is a longitudinal population-based regional cohort study, designed to assess an extensive range of exposures and a wide range of health-related outcomes over a long period of time. It serves as an integrated platform for investigating the interplay of environment, lifestyle and ‘-omic’ (such as genomics, metabolomics, transcriptomics, proteomics) factors that increase individual and community risk of developing cancer and other common adult diseases. The intent is to engage participants in ongoing data collection over their lifespan, to follow them over time both actively and passively, and to make genomic, environmental, lifestyle and electronic health-related data available to the scientific research community. Derived variables, including data generated from biologic samples, are returned to the cohort to further enrich the data holdings. The OHS is a major contributing cohort within the national Canadian Partnership for Tomorrow’s Health (CanPath; CanPath.ca),9 a pan-Canadian cohort with >330 000 participants, that includes seven regional cohorts spanning all 10 provinces: BC Generations Project,10 Alberta's Tomorrow Project,11 Healthy Future Sask (Saskatchewan), Manitoba Tomorrow Project, CARTaGENE (Quebec)12 and the Atlantic Partnership for Tomorrow’s Health.13 Mandated recruitment goals were surpassed, and both the OHS and CanPath are the largest volunteer cohort studies ever conducted in Canada. The collection of baseline data, core biologic samples and physical measures was harmonized across CanPath.14 Close collaboration between cohorts provides a coordinated infrastructure, large scope and concomitant statistical power to address important scientific questions and capitalize on rapidly evolving high-throughput technologies. The provision of re-contact enables the cohort to be adaptive in supporting ongoing and future activities, including responses to emerging public health priorities such as the COVID-19 pandemic and the impact of climate change on health. Adult residents of Ontario aged ≥18 years were eligible to participate in the OHS. Eligible participants had to be sufficiently proficient in English or French to provide informed consent and have access to the internet to complete the baseline questionnaire. Participants were recruited primarily through invitation e-mails and letters (based on purchased and commercial mailing lists), e-mail invitations to employees at large organizations, advertising (i.e. newspaper ads, public transit ads, local media and social media, e.g. Twitter and Facebook), community events (e.g. farmer’s markers), through targeted recruitment initiatives in partnership with primary care providers (e.g. family medicine practices, Family Health Teams, community health centres) and other stakeholders (e.g. the YMCA, large companies, charities, disease advocacy groups, unions, and government agencies), incentive programmes (i.e. Air Miles, gift cards) and through friend and family referrals. The OHS partnered with the Canadian Alliance for Healthy Hearts and Minds Study to jointly recruit participants of African, Chinese and South Asian ethnicities using ethnically targeted recruitment strategies.15–17 Potential participants registered to participate in the OHS through the study’s website. Participants provided informed consent to participate in the study; completed the baseline questionnaire; consented to share these data with other researchers; to link these data with regional, provincial, and national administrative and health-related databases; and to be re-contacted in the future for multiple study-related purposes. The OHS also developed temporary, community-based study centres to collect biospecimens and physical measurements from new and existing OHS participants, to broaden the outreach of the OHS to under-represented portions of Ontario and allow the study to engage participants in regions with a substantial participant base. A local media campaign was conducted ∼2 weeks prior to the deployment of a community-based assessment centre to encourage participation from both current and potential new participants. After a pilot phase, recruitment into the main phase of the OHS ran from September 2010 to March 2017 with 225 620 participants enrolled [137 918 (61%) female and 87 702 (39%) male]. The mean (SD) age at enrolment was 46 (15) years (Table 1), ranging from 18 to 97 years. At baseline, 40 034 participants (18%) provided a blood sample, 12 818 (6%) underwent a series of physical measurements and 12 600 (6%) provided urine samples. From 2020 to 2021, 9956 blood spots were collected, including 3164 from participants who did not provide a previous sample, increasing the total number of participants who have provided a biological sample to 43 198 (19%). Compared to the Ontario population aged ≥18 years, the study population is overrepresented for women (61% vs. 51%), overrepresented for adults with a university degree (77% vs. 55%) and under-represented for minority populations (20% vs. 33%), including immigrants (21% vs. 33%) (Table 1). The OHS is geographically diverse, with proportional representation from urban and rural areas across each of Ontario’s public health units (Figure 1).18 Less than 5% of OHS participants have asked not to be re-contacted; the majority of these participants indicated that the data and samples they have provided may continue to be used for research purposes. Geographical distribution of participants by Ontario public health unit, based on self-reported postal code at enrolment. The Ontario Health Study (OHS) has representation across each of Ontario’s public health units, with enrolment greatest in catchment areas for the City of Toronto Health Unit (n = 45 367), followed by the City of Ottawa Health Unit (n = 24 194) and Peel Regional Health (n = 17 114). Enrolment is roughly proportional to the size of the populations served Socio-demographic characteristics in the Ontario Health Study (OHS) and the general population of Ontario, mean (SD) or % 2016 Ontario census profile; restricted to include data for people aged ≥18 years. Visible minorities: persons, other than Indigenous peoples, who are non-Caucasian in race or non-white in colour; multiple visible minorities: respondents who reported more than one visible minority group. Participants are followed both actively and passively via linked administrative health data for their entire lifespan and have the option of selecting the communications they would like to receive through their participant home page. The first follow-up questionnaire was administered between November 2016 and April 2018, and was completed by 47 772 participants (21%). The work-history questionnaire was administered from March 2019 to December 2019 and was completed by 33 782 participants (15%). The COVID-19 questionnaire was made available online from May 2020 to November 2020 and was completed by 42 145 participants (23%), the first dried blood spots were collected from March 2021 to June 2021 from 9956 participants, and second dried blood spots were collected from October 2021 to July 2022, with third blood spots and corresponding questionnaires being collected presently. Ontario has universal, publicly funded coverage for necessary physician and hospital services, and those aged ≥65 years have universal prescription drug coverage. ICES, a not-for profit provincial research institute (ices.on.ca), houses the electronic data repository consisting of record-level, routinely collected health data that is coded and linkable. Included are derived chronic condition cohorts developed at ICES using linked data algorithms applied to physician billing claims, hospitalization records, emergency department visits, outpatient procedures, day surgeries, prescription drug dispensation records from outpatient pharmacies and laboratory data sets. These sources include dates of service and diagnosis codes, where applicable. Hospitalization records, for example, include ≤25 diagnoses codes recorded using ICD-10-CA (i.e. enhanced Canadian revision) for each hospital stay. Emergency department visit records also include the chief complaint. Linkage with administrative and health-related databases,37 including the Ontario Cancer Registry (OCR)38 and the ICES-derived cohorts of chronic conditions,39–47 allows passive follow-up of participants for future disease endpoints, as well the capture of a rich array of clinical data to support health services research (Box 1). The provision of a participant’s Ontario Health Insurance Plan (OHIP) number enables deterministic data linkage, and probabilistic linkage is carried out to link data sources for those who chose not to provide their OHIP number; 188 351 participants (83%) consented to administrative linkages and were successfully linked. Deaths are confirmed through linkage with the all-causes mortality file from the Ontario Registrar General. The OCR uses the collaborative staging method consistent with the tumour, node, metastasis staging system48 to capture cancer stage data elements which can be integrated with treatment data, and cancer histotype is coded using International Classification of Diseases for Oncology codes.49 Questionnaire data, physical measurements, biological samples and linked environmental and health data Core questionnaire (n = 225 620) Socio-demographic: of status, Family family family of cancer and other major diseases Health health status, of cancer and other diseases, history, (i.e. cancer physical and current environmental current and and measurements (n = 12 and and and heart and of the heart and (n and (n questionnaires (n = 47 to core questionnaire Cancer treatment type of physical to environment (n = 33 samples blood blood or blood in or (n = 40 in (n urine (n = 12 blood spots (n = (n = (e.g. time of complete blood (n = environmental measurements (n = 225 620) and social access to to and urban and urban public Air climate local climate health data (n = 188 Ontario Cancer Registry all-causes mortality file from the Registrar primary care data, physician billing (OHIP) data, ICES-derived cohorts of chronic the Canadian the Ontario COVID-19 data (n = 42 COVID-19 and health with a and factors status, and dates spots and (n = (n = ongoing and of cancer, and of chronic diseases and measures of health services are in and for the cohort and for the subset who provided blood samples. of participants a common chronic condition at and asthma (Table to of these Canadian adults and and support an period of many have including and cancer (Table have also type 2 and of asthma (Table such as these a wide range of and linkages are the prospective blood and the in time from blood collection to diagnosis available as data at the study provides a to study a range of to disease and natural and COVID-19 were through linkage with the Ontario available as data at which facilitate ongoing COVID-19 studies and those of the long-term of and of cancer in the Ontario Health and those who provided a blood participants who consented to administrative mean (SD) age in years is 47 (15) and those who provided a blood through linkage with the Ontario Cancer Registry from through to of self-reported cancer is also through linkage with the Ontario Cancer Registry the period from baseline to March follow-up time is total of and of chronic diseases and health services in the Ontario Health and those who provided a blood participants who consented to administrative linkages and were successfully outcomes were through linkage to the disease developed by mean (SD) age in years is 47 (15) and those who provided a blood through linkage with the disease the period from baseline to March 2020 with the of heart which was through to March chronic A of the data collected, or available through can be in questionnaires are available at and follow-up questionnaire data are collected using a data include and family health exposures to and and information on and of (Box and The first follow-up questionnaire an on and exposures of with new including those on and and health. A work-history questionnaire collected data on previous including type of physical of the to (e.g. characteristics and the environment of the characteristics in the Ontario Health and by mean (SD) or % to the of the study population who completed the first follow-up questionnaire. to the of the study population who provided physical measures. not International urine and physical measures (Table were collected from of participants recruitment (Box 1). Participants aged years were eligible for the provision of a blood sample through one of the community-based assessment centres or through a participants provided of the type and time of the and other than were was into of blood and to support and or for These are at a for future A of the blood samples underwent to complete blood and from participants have on the array and whole-genome on is with whole-genome completed and to the of participants who provided a blood The OHS has partnered with Canada’s Data Linkage and the Canadian Health to collect environmental data. has a of environmental factors (e.g. local of access to social climate and to the for each postal code in Canada. The the potential of data across multiple (e.g. by linked the to collect information from participants. OHS previous have through a using data from at Canada. provides the environmental data for each postal code to the these data are linked and the OHS is provided with the environmental data (Box the for each of an exposures to environmental factors change on can the of data be over the of exposures are to Canadian postal codes, which in size between urban postal code and rural postal than of the Canadian population in urban where postal codes one of a exposures to and are across the study sample, for environmental health-related research (Figure of the measures of and From to are and The for each is the for all of Canada in which the in are of the The for each is the distribution in the Ontario Health Study (OHS) In 2020, in to the COVID-19 an online questionnaire was across to collect data COVID-19 hospitalization or care, current health and risk factors, potential of impact of pandemic on and impact of pandemic on social and In dried blood were collected from almost 10 000 OHS participants and for to of and using a of high-throughput in the study also provided data on COVID-19 exposures and with new data on with risk of to and dates of A number of studies have completed or are including one OHS participants that collect data on and and a second OHS participants that of the heart and and collected data on cardiovascular risk The OHS has supported a of research across many that to better the of health and A of scientific can be at A of the research to include the In a study of the risk factors for cancer, and of cancer were associated with increased risk of cancer age investigating a array of health outcomes was associated with and disease in as an important link between and was not associated with type 2 or that is not a major risk for cardiovascular increased total physical and were associated with of were more to suffering from health to access and people who in with a of on their health and studies the of the In a that the risk across cohorts better than a derived from a cohort In study, of cancer in of by and in the to years prior to diagnosis by were applied not to the of cancer, also to the a early cancer In research to the of blood study developed a blood health risk from complete blood and that those with blood were to be with cardiovascular and diseases, and with of in and blood and indicated that of was associated with blood the potential to to the of study was at understanding the of and in health including risk of that that to is as as reported with to in 10 a large and that the size and of in the understanding of the of in blood to cancer was a the responses were by with followed by followed by were associated with time second increasing of cancer and with previous responses to those for The OHS has characteristics make the study a and powerful research is large in and a and sample of the Ontario is a platform for health has online from the data and is integrated with core in Ontario who are The study has recruited of the adult population of Ontario, including ethnically and geographically and participants. In the study has in the age to that has to engage in many other large cohort studies. The study is and was to participants of or general disease or clinical The cohort who were to and in in a research study and are between the study sample and the general and research has from cohort studies conducted within is in exposures of study for example, capture in status, and health and be to both assess the between these and outcomes of and for these variables, as A of one of recruitment an incentive based on gift or Air Miles, is that the incentive increased enrolment in the participants who were recruited using were to to follow-up studies or provision of biologic samples. have a of cohort members who are across study of those who completed the follow-up provided a blood sample and of those who completed the work-history provided a blood may mean that the OHS is not for research to the number of participants who provided statistical power be by the that the OHS is of a pan-Canadian population cohort that has 000 baseline biospecimens the OHS being the largest contributing cohort to The OHS and the other cohorts of CanPath are to both across Canada and The OHS for example, made to across a number of to power Participants are followed both actively and passively via linked administrative health data for their entire with ICES, the OHS is linked administrative clinical data from rich data of comprise of the Canadian and an complete resource for and outcomes with Cancer Ontario have on cancer from the The OCR has a high of data from the that each Canadian and has a for cancer collection and of are based on a death and are capture have for and a the OHS is designed to for many with to the data with follow-up studies and the OHS participants for data the of which both the questions that can be using the resource and the to for the potential of as Ontario is as a major centre for research and is home to and research have that the OHS. The OHS is at and in by the Ontario for Cancer which also the Alliance for the Canada Canadian Data is in the International Cancer These are to supporting study priorities including the of and data and participation in cohort is at the of which the of the and the of data, on the national and researchers visit the OHS to an of and for a data access to the out an access form and with an research of of scientific and a of the is for by the data access a of support for a or by a access studies biological samples, be to those that are and scientific as by the of access to data biosamples be for the of time out in the a be between the and the OHS. the OHS for to OHS and can also be to [email The OHS not administrative health data or cancer data. These data can be linked to OHS data through ICES or Ontario Health and access can be provided to researchers to prospective in access to data and samples from multiple regional cohort studies in CanPath visit the The OHS is by the of Toronto Health The data be OHS access that can be at process includes of a research by the data access of a between the and the and by the data are available at have to the and of the study; and to the cohort. conducted or the of the data and the in the with support from and provided and the research, and The Ontario Health Study is supported by the Ontario for Cancer which is funded by the Ontario of and Ontario which is funded by the Ontario of Health and which is funded by the of and Health Ontario, which is funded by the of Health and and the Canadian Partnership which is funded by Health Canada. The COVID-19 was funded by the Canadian for Health and the COVID-19 CanPath is by the of of Health with national from the Canadian Partnership study ICES Data and used data from the ICES Data which is by ICES with support from and Canada’s for the Ontario the Canadian of Health and the of The and reported are those of the by ICES or of or is or be of are based on data and information provided by Ontario Health Cancer the and are those of the and not those of Ontario and to postal codes, were provided by Health The the participants who their information and biological samples, and the of the OHS for their important

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