Preventing disease before it occurs—or catching it early when treatment is most effective—represents one of medicine's greatest opportunities to improve health and save lives. Yet Canada's healthcare system remains primarily oriented toward treating illness rather than preventing it. Preventive care and screening programs exist but are unevenly implemented, inconsistently accessed, and often underprioritized in healthcare funding and policy. Understanding the potential and limitations of prevention is essential for improving Canadian health outcomes.
What Is Preventive Care?
Levels of Prevention
Public health distinguishes several levels of prevention. Primary prevention aims to prevent disease from occurring in the first place—through vaccination, health promotion, or addressing determinants of health. Secondary prevention detects disease early through screening, enabling treatment before symptoms appear or conditions worsen. Tertiary prevention manages existing disease to prevent complications and maintain quality of life.
This summary focuses primarily on secondary prevention—screening programs that detect disease or risk factors in apparently healthy people. These programs represent a significant but contested component of preventive healthcare.
Effective Screening
Not all screening is beneficial. Effective screening programs must meet several criteria: the condition must be important enough to warrant intervention; there must be a reliable test that distinguishes those with the condition from those without; there must be effective treatment that works better when applied early; and the benefits of screening must outweigh the harms of false positives, overdiagnosis, and unnecessary treatment.
These criteria are more stringent than often assumed. Many intuitively appealing screening ideas fail when subjected to rigorous evaluation. Screening can cause harm—through anxiety from false positives, complications from unnecessary procedures, and treatment of conditions that would never have caused problems. Evidence-based medicine demands that screening programs demonstrate net benefit before widespread implementation.
Cancer Screening in Canada
Breast Cancer Screening
Mammography screening for breast cancer is one of Canada's most established screening programs. Most provinces recommend screening every two to three years for women aged 50 to 74, though recommendations vary and debates continue. Mammography can detect breast cancers before they're palpable, enabling earlier treatment. However, screening also produces false positives leading to unnecessary biopsies, and overdiagnosis of cancers that would never have become clinically significant.
Debates about when to start screening and how often to screen reflect these trade-offs. Some advocates push for earlier and more frequent screening; others argue that the harms of overscreening are underappreciated. Evidence is interpreted differently by different groups, and patient values about trade-offs between risks and benefits vary.
Cervical Cancer Screening
Cervical cancer screening through Pap tests has dramatically reduced cervical cancer mortality. Canada is transitioning from Pap tests to HPV testing, which is more effective at detecting precancerous changes. Vaccination against HPV further reduces cervical cancer risk, with prevention becoming primary rather than secondary.
Screening participation varies significantly, with some populations—including Indigenous women, immigrants, and those with lower incomes—having lower screening rates. Barriers include access to healthcare, discomfort with the procedure, and lack of awareness. Reducing these disparities requires addressing both healthcare access and cultural factors.
Colorectal Cancer Screening
Colorectal cancer screening through fecal tests, colonoscopy, or other methods can detect cancers early and identify precancerous polyps that can be removed. Screening reduces colorectal cancer mortality. Yet participation rates remain lower than for breast or cervical screening. The unpleasantness of the screening process, particularly colonoscopy, creates barriers.
Lung Cancer Screening
Low-dose CT screening for lung cancer in high-risk individuals—primarily current or former heavy smokers—is relatively new. Evidence shows mortality reduction, but implementation has been slow. Questions remain about how to identify eligible populations, how to manage findings, and how to ensure equitable access.
Cardiovascular Risk Assessment
Cardiovascular disease is a leading cause of death in Canada, but unlike cancer, it doesn't have a single screening test. Instead, prevention involves assessing multiple risk factors—blood pressure, cholesterol, blood sugar, smoking, family history—and intervening based on overall risk. Medications like statins can reduce risk in those with elevated cardiovascular risk.
Debates in cardiovascular prevention involve where to set treatment thresholds. Expanding the definition of elevated risk means treating more people who might benefit—but also treating people who would never have had cardiovascular events. Medicalization of risk factors raises concerns about the pharmaceutical industry's influence on prevention guidelines.
Screening Disparities
Who Gets Screened?
Access to screening is not equal across the Canadian population. Those without family doctors may miss screening recommendations. Rural and remote populations face geographic barriers. Indigenous peoples experience screening rates below the general population for several cancers. Immigrants, particularly recent arrivals, may have lower screening participation. Socioeconomic status correlates with screening uptake.
These disparities matter because they reproduce and amplify broader health inequities. Populations already disadvantaged may miss opportunities for early detection, leading to later-stage diagnosis and worse outcomes. Equitable prevention requires addressing these access gaps.
Tailoring vs. Universality
Population screening programs aim for universal coverage, but some argue for more tailored approaches. Risk-stratified screening would offer different screening intensity based on individual risk factors. Genetic testing can identify those at higher risk for certain cancers. Personalized prevention could improve efficiency by focusing resources on those most likely to benefit.
However, personalized approaches raise equity concerns. Those with access to genetic testing and risk assessment may receive better-tailored prevention while others receive less. Universal programs, though potentially less efficient, may be more equitable.
Primary Prevention
Vaccination
Vaccination represents the most successful preventive intervention in medicine's history. Routine childhood vaccination prevents numerous diseases. HPV vaccination prevents cervical and other cancers. Influenza vaccination reduces seasonal illness and mortality. COVID-19 vaccination demonstrated both the potential and challenges of rapid vaccine deployment.
Vaccine hesitancy has emerged as a significant concern. Misinformation spreads rapidly through social media. Some populations have historically been harmed by medical research and have legitimate distrust. Achieving high vaccination coverage requires addressing both misinformation and trust.
Health Promotion
Much disease is preventable through behaviour change—reducing tobacco use, improving diet, increasing physical activity, moderating alcohol consumption. Public health campaigns aim to promote healthy behaviours, though their effectiveness varies. Individual behaviour change is difficult, and structural factors—food environments, built environments, economic circumstances—shape behaviour in ways that individual-focused interventions cannot fully address.
Social Determinants
Many determinants of health lie outside healthcare entirely. Income, education, housing, employment, and environment all shape health outcomes. Addressing these social determinants may prevent more disease than medical interventions. Yet health policy often focuses on healthcare while neglecting the broader factors that create health and illness.
Healthcare System Orientation
Treatment vs. Prevention
Canada's healthcare system is oriented primarily toward treating illness rather than preventing it. Hospital and physician services—the core of medicare—are reactive to existing disease. Prevention receives a small fraction of healthcare spending. Public health agencies responsible for prevention are chronically underfunded and have limited authority.
This orientation has historical roots but continues because acute care has more visible, immediate beneficiaries. Prevention's benefits are diffuse and future-oriented—people don't know when they've been prevented from getting a disease. Political incentives favour visible interventions over invisible prevention.
Primary Care's Role
Family doctors and primary care teams are meant to deliver preventive care—screening, vaccination, counselling—but face constraints. Appointment time is limited. Fee structures may not reward prevention. Patients come with immediate concerns that crowd out prevention discussions. Team-based care models can expand preventive capacity, but these models are not universally available.
Questions for Further Discussion
- How should decisions about population screening programs balance evidence of benefit against potential harms from overdiagnosis and overtreatment?
- What approaches can reduce screening disparities and ensure equitable access to preventive care?
- How much should healthcare spending shift from treatment to prevention, and what would enable such a shift?
- What is the appropriate role of individual behaviour change versus structural interventions in disease prevention?
- How should prevention programs address populations with lower trust in healthcare institutions?