The British Whitehall studies helped establish the importance of the social determinants of health, while a Danish study of children provided strong evidence to disprove the damaging MMR-vaccine-causes-autism hypothesis.
Those are just two of many international cohort studies—studies that follow large groups of people over many years.
In Canada, starting such studies has never been easy because of the challenge of securing long-term funding commitments and harmonizing the collection of data across provincial and territorial jurisdictions.
But in the past decade or so, important Canadian cohort studies have been launched in order to shed light on the impact that crucial biological and environmental risk factors have on the development of cancer and other chronic diseases. Five regional cohort studies together comprise the Canadian Partnership for Tomorrow Project (CPTP), launched in 2008 as a national research platform.
Canadian advantage is the ability to link to health care records
Canada’s particular advantage in launching cohorts is the potential for record linkage–linking information gathered from study participants to provincial health care data, says John Potter, who is chair of the governance committee of the CPTP. A New Zealander, Potter is a physician epidemiologist, whose speciality is studying the causes and prevention of cancer. He has extensive international experience with cohort studies.
The size of the combined CPTP, together with the ethnic diversity of Canadians, will also present a huge opportunity to facilitate study of the causes of cancer and common chronic diseases and contribute to knowledge, he says. He adds that in his experience, once people become involved in cohort studies, they are “incredibly generous” with their time, allowing for extensive follow up.
By far the largest of the five regional cohorts is the Ontario Health Study (OHS), which began collecting information in late 2010. Other studies under the CPTP umbrella include three projects launched in 2009—the BC Generations Project, Quebec’s CARTaGENE, and the Atlantic PATH—as well as Alberta’s Tomorrow Project.
The Alberta cohort was originally launched in 2000 and information was gathered only by a questionnaire. When it joined the CPTP, the Alberta project began collecting blood and urine samples at study centres in Calgary and Edmonton, as well as at a mobile unit.
About 240,000 volunteer participants have completed the OHS online health questionnaire. Of the Ontario total, about 45,000 have donated blood samples (the goal is 60,000), while another 10,000 (out of the 20,000 goal) have undergone a more comprehensive assessment at Women’s College Hospital in Toronto, says OHS executive scientific director Lyle Palmer.
Ontario cohort relies on volunteers completing a web-based questionnaire
Although OHS participants are volunteers, they are “broadly representative” of the Ontario population, based on census parameters, he says. In terms of ethnicity, Aboriginals are slightly over represented while East Asians are under represented, he says. As well, because participants were originally recruited from universities and hospitals, there’s also “a slight bias” towards participants who are more educated, wealthier and urban dwelling.
The study, which began collecting information in late 2010, is the first prospective cohort study in the world to rely exclusively on a web-based questionnaire for recruitment and to collect baseline information, says Palmer. Total funding from 2007 to March 31, 2013 is just under $30-million, and the study has funding commitments from the province (through the Ontario Institute for Cancer Research) and the federal government (through the Canadian Partnership Against Cancer) to 2017, he says.
OHS participants can agree to have the information they provide in the online questionnaire be linked to their Ontario health care data (they can remain in the study if don’t agree to linkage), and they will be asked to fill out subsequent questionnaires that may probe in more depth particular areas such as their exercise and eating habits. Participants also are given their own “homepage” and those who provide blood samples will be notified of the results.
Still, the study is “thin”— in terms of the information and biological samples that it collects—compared to many international cohort studies and some other, smaller, Canadian cohorts.
For example, only blood is collected from the largest subset of enrolees, while some other studies in the Canadian Partnership for Tomorrow also collect urine and other biological samples.
But cohort studies can differ and the OHS is designed as a platform, or sampling, study that will make its information available to “good researchers with good questions,” Palmer notes. Researchers could well obtain their own funding if they want to collect more information from study participants.
Scope of Ontario study expanded: more recruits, fewer samples
The size and scope of the OHS changed considerably when Palmer, a genetic epidemiologist, took over the reins two and half years ago. It was first envisioned to be primarily about genetic and environmental risk factors for cancer, and more information and biological samples would have been gathered from a smaller number of recruits, aged between 35 and 69 years old.
The revised OHS is casting a wider net in terms of the age of participants—now between 18 and 69—and more scientists and researchers from a wider range of health disciplines are involved in the study design, thus expanding the scope of conditions it is hoped that the cohort will shed light on.
The target cohort size has also expanded—from an original 150,000. Palmer says his “aspirational” goal is now to enlist 1-million participants.
The role of environment was to play a larger part in the original study. In addition to blood and urine samples, researchers were hoping to collect water and dust samples from people’s households, and get radon measures from Health Canada, says Shelley Harris, an epidemiologist specializing in occupational and environmental health with Cancer Care Ontario who worked on the original proposal.
Although it would have been very costly to collect and analyse such information, it would have allowed for more study of the interaction of genes and the environment, Harris notes. Still, some measures to study environmental exposure can be added, such as mapping people’s home and work location histories against known environmental exposures.
Harris notes that the broader age group in the current OHS means women of childbearing age are now part of the cohort and “we rarely have good information about women in their reproductive years.
Blood samples vital part of all five regional cohort studies
The regional studies that make up the CPTP project differ slightly in their focus but all ask a core set of questions, and involve participants between 35 and 69 years of age, says Jacques Magnan, senior scientific lead for the project. An important goal for all member cohorts is to collect a robust number of blood samples, so researchers can look for molecular markers of people who develop a particular disease compared to those who don’t, which could provide opportunities for prevention approaches. As well researchers can track markers for information about nutrition and hormone levels, as well as some environmental exposures.
The recruitment goal for CPTP is 300,000, which has almost been met (the OHS will account for half of the total number of recruits 35 to 69 years of age) and the project is also linked up with international cohorts, through the Public Population Project in Genomics.
For the five years ending March, 2012, the CPTP spent about $100-million, says Heather Bryant, vice president of cancer control at the Canadian Partnership Against Cancer (CPAC). THe partnership, the single largest funder, contributed $40-million to that total, with the balance from co-funders including the BC Cancer Foundation, Alberta Innovates-Health Solutions, the Alberta Cancer Society, the Alberta Cancer Prevention Legacy Fund, the Ontario Institute for Cancer Research, Public Health Ontario, Genome Quebec, Genome Canada and the Canadian Foundation for Innovation.
Planning and recruitment is “the most expensive phase” of cohort studies, she says, adding that the project is now in the “building phase” which should be completed by March 2015.
Information and samples to shed light on cancer, chronic diseases
Although a key focus is cancer, the cohort studies are gathering information and biological samples that will be useful to study a wide range of chronic conditions and illnesses, such as diabetes and heart disease, and to assess the contribution of genetics, lifestyle, environment and diet to the development of illness.
A very different type of cohort study from the OHS, and the only Canadian cohort to receive Canadian Institute for Health Research (CIHR) funding, is the Canadian Longitudinal Study on Aging (CLSA). It began recruiting in 2009 with the goal of studying the “trajectory and transitions” in health of 50,000 participants, selected on a randomized basis, between 45 and 85 years old, says principal investigator Parminder Raina, a professor of clinical epidemiology at McMaster University.
The Canadian Partnership for Tomorrow Project stands as the largest cohort ever launched in the country and it is based on a high level of inter-regional cooperation to assure that complementary information is gathered from recruits in the different regions.
It should provide a rich resource for researchers studying important aspects of the development of cancer and chronic diseases. Some of those researchers will likely look for funding from the CIHR, the Canadian Cancer Society Research Institute and the Heart and Stroke Foundation—organizations that may play an important role helping to sustain the project over the long term.