HLTH 101: Introduction to Health

Sources and References

Primary textbook — Jennifer Irwin, Shauna Burke, Paul Insel, Walton Roth, Core Concepts in Health, 4th Canadian ed. (McGraw-Hill Education Ltd. Canada, 2023). Supplementary texts — Dennis Raphael (ed.) Social Determinants of Health: Canadian Perspectives; Michael Marmot The Health Gap; Abdel Omran “The Epidemiologic Transition”. Online resources — AFMC Primer on Population Health; Public Health Agency of Canada reports; Canadian Institute for Health Information; Statistics Canada health statistics; Global Burden of Disease Study / IHME; WHO World Health Report.

1. Defining Health — Biomedical, Behavioural, and Social-Ecological Models

Ask ten people what “health” means and most will say “the absence of disease.” That is not wrong but it is incomplete, and the history of modern public health is largely the story of how the definition of health has widened. The model you carry in your head silently dictates what counts as a health problem, who is responsible for fixing it, and which interventions look plausible.

The biomedical model dominated nineteenth- and early twentieth-century medicine. It treats the body as a machine, disease as a malfunction of specific parts, and the physician as a technician who isolates the fault and repairs it. Its conceptual parents are germ theory, anatomy, and cellular pathology; its triumphs include antisepsis, vaccination, insulin, and antibiotics. The model assumes that for every disease there is an identifiable cause and that treating the cause cures the disease. This logic was so successful at taming infectious illness that it still structures hospitals, medical schools, and research funding. But it struggles with almost everything else: it has little to say about why one smoker gets lung cancer and another does not, why depression clusters in poor neighbourhoods, or why heart disease rates fell before any major new treatment appeared. These are patterns that emerge from the interaction of bodies with environments.

The World Health Organization widened the frame in 1948: “Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” The definition is aspirational and has been criticized as utopian, but it named mental and social dimensions as equal to the physical and decoupled health from diagnosis.

The behavioural model zooms in on what individuals do — smoking, diet, alcohol, exercise, sleep, seatbelt use. A large body of evidence shows these account for meaningful variation in morbidity and mortality. The model is appealing because it suggests a clear lever, but it tends to stop at the skin of the individual, missing the structural conditions that shape which choices are available.

The social-ecological model is the synthesis most contemporary courses teach. It arranges determinants in concentric rings: the individual at the centre (biology, personal behaviours), surrounded by interpersonal relationships, then institutional and community factors (schools, workplaces, neighbourhoods), and the outermost rings of policy and society. A teenager’s decision to smoke is shaped by peers, advertising, tobacco taxation, and retailer density. The ecological framing makes it natural to ask not only what a person does but what conditions surround them.

A related concept is wellness, the active pursuit of optimal health across multiple dimensions — physical, emotional, intellectual, interpersonal, spiritual, environmental, occupational, financial. Wellness is less a state than a practice, and the dimensions interact: financial stress worsens sleep, loneliness raises cardiovascular risk, purposeful work buffers depression.

Health is also a moving target. The problems of twenty-year-olds in 1920 (tuberculosis, typhoid, maternal mortality) are not those of twenty-year-olds today (anxiety, obesity, substance use, traffic injury). Any definition has to be historicized.

2. Determinants of Health — A Framework

A determinant of health is any factor that influences health outcomes. The word “determinant” is slightly misleading — these factors shape probabilities rather than dictate fates — but it captures the key insight that health is not randomly distributed. The Public Health Agency of Canada lists twelve determinants: income and social status, employment and working conditions, education and literacy, childhood experiences, physical environments, social supports and coping skills, healthy behaviours, access to health services, biology and genetic endowment, gender, culture, and race/racism. The AFMC Primer on Population Health adds that these factors interact and compound over a lifetime, and that the distribution of health in a population is almost always more revealing than the average.

A useful distinction is between proximal, intermediate, and distal determinants, sometimes called downstream, midstream, and upstream. Proximal (downstream) factors are the things closest to disease in the causal chain: a clogged artery, a high blood pressure reading, a fasting glucose number. Intermediate (midstream) factors are the behaviours and exposures that produce those proximal states: diet, physical activity, smoking, stress. Distal (upstream) factors are the conditions that shape those behaviours and exposures: income, education, housing, neighbourhood, policy. A clinician treats downstream; a public health department works midstream; a government budget acts upstream.

The metaphor the field likes to use is John McKinlay’s story of the river. You see people drowning downstream and you pull them out one by one — that is clinical medicine. Eventually you are so busy pulling people out that you never go upstream to find out why they keep falling in. Upstream thinking means asking who is pushing them, what the bridge is made of, and whether the path to the bridge is fenced. It does not replace pulling drowning people out of the water; it asks whether drownings can be prevented at lower cost and less suffering by changing conditions further back.

Upstream factors tend to have larger, more durable effects than downstream ones, but they are harder to measure and politically harder to change. A clean-water act, a housing subsidy, or an early-childhood education program may do more for a population’s health over thirty years than a new drug, but the benefit is diffuse and the causal chain is long. Canadian public health scholarship — associated with thinkers like Dennis Raphael, Nancy Ross, and the late Hertzman — has argued consistently that Canada over-invests in downstream medical care and under-invests in the upstream conditions that do most of the work. The debate is not whether hospitals matter; it is whether the marginal health dollar would buy more years of life in a cardiac unit or in an early-learning classroom.

A second framework worth knowing is Michael Marmot’s social-gradient argument. In his Whitehall studies of British civil servants, Marmot showed that health outcomes followed the hierarchy of employment grade in almost perfectly graded steps — senior civil servants were healthier than middle civil servants, who were healthier than junior civil servants, even though none of them were poor in absolute terms and all had equal access to the National Health Service. The gradient was not an artifact of smoking or diet; those explained some of it but not most. What seemed to matter was control: where you sat in the hierarchy determined how much say you had over your daily life, and low control over time corroded the body through chronic stress. Marmot’s book The Health Gap argues that the gradient is everywhere and that closing it requires acting on the conditions of daily life — the material and psychosocial resources people have to shape their circumstances.

3. Social Determinants of Health in Canada

If upstream factors matter, which matter most in Canada? Raphael’s Social Determinants of Health: Canadian Perspectives converges on a handful of drivers.

Income and its distribution. Income is the single strongest social predictor of health in wealthy countries. The relationship is non-linear — an extra thousand dollars buys a lot of health for a low-income family and very little for a high-income one — but the gradient continues far up the distribution. Statistics Canada analyses show life-expectancy gaps of seven to eleven years for men between the highest- and lowest-income neighbourhoods in major Canadian cities. What money buys is nutritious food, stable housing, safer neighbourhoods, time for sleep and exercise, and distance from the toxic stress of scarcity.

Education correlates with health partly through income, but also through health literacy, ability to navigate complex systems, and a sense of agency. Employment and working conditions matter too: unemployment is bad for health, and so is precarious, low-control, high-demand work. The job-strain model (Karasek) and effort-reward imbalance model (Siegrist) describe configurations — high demands with low autonomy, or large efforts poorly rewarded — that predict cardiovascular disease, depression, and musculoskeletal complaints.

Early childhood development shapes brain architecture, stress regulation, and social-emotional skills in ways hard to remediate later. Clyde Hertzman argued investments in early childhood pay health dividends for decades, and the Adverse Childhood Experiences (ACEs) literature shows a dose-response between childhood adversity and adult chronic disease.

Food insecurity affects about one in six Canadian households, much more in Nunavut and among single-mother, Indigenous, and Black households. Housing — adequate, affordable, stable — is a health input; homelessness dramatically shortens life expectancy, and inadequate housing harms respiratory, mental, and developmental health.

Indigenous status. First Nations, Inuit, and Métis peoples experience health disadvantages reflecting the continuing effects of colonization, residential schools, land dispossession, and systemic racism. Life-expectancy gaps, higher rates of diabetes and tuberculosis, and suicide rates many times the non-Indigenous average in some communities are not explained by biology. The Truth and Reconciliation Commission’s Calls to Action include health-specific items, and cultural safety is now part of Canadian medical education.

Racism operates as both acute stressor (experiences of discrimination) and structural force (housing, employment, policing, healthcare access). Gender shapes exposures, behaviours, biological susceptibility, and how the healthcare system responds — women’s pain is more often dismissed, cardiovascular symptoms more often missed. Social inclusion is also an exposure; isolation and thin social ties predict worse outcomes.

Two themes run through all of these. First, the determinants cluster and compound: low income tends to come with less education, worse housing, precarious work, and more exposure to racism. Second, they interact with biology: chronic stress produces inflammation, cortisol dysregulation, and cardiovascular wear that embeds social disadvantage in the body — biological embedding.

4. Measuring Health — Mortality, Morbidity, and Composite Measures

Before you can act on health you have to measure it. Health measurement is not just a technical exercise; the choice of measure shapes priorities, because what gets counted gets done.

The oldest health measure is mortality: who dies, at what age, of what cause. The crude mortality rate is deaths per 100,000 people per year. It is crude because populations differ in age structure, and since death rises sharply with age, an older population will have a higher crude rate even if its age-specific risks are lower. Age-standardized mortality rates correct for this by applying a common age structure, allowing comparisons across places and times.

Cause-specific mortality rates answer different questions (“how much cardiovascular death is there?”). Case-fatality rate — the share of people with a given disease who die of it — measures severity once disease occurs. Infant mortality (deaths before age 1 per 1,000 live births) is a famously sensitive indicator of general social conditions; it is low in Canada (about 4–5 per 1,000) but varies meaningfully across provinces and neighbourhoods.

Life expectancy is the average number of years a person would live if current age-specific mortality rates held constant. A life expectancy of 82 does not mean babies born this year will live to 82; it means if you froze today’s mortality pattern forever, their average lifespan would be 82. Canadian life expectancy rose from about 59 in 1921 to about 82 in the 2020s, with most of the gain coming from falling infant and child mortality, not from elders living longer. A recent, unsettling trend is the stall and brief reversal of life expectancy growth in Canada and the United States, driven in Canada by opioid-related deaths and, during the pandemic, by COVID-19.

Mortality has an obvious limitation: many diseases do not kill people — they just make their lives worse. Morbidity measures capture this. Incidence is the number of new cases of a disease in a population during a defined period (e.g., new diabetes diagnoses per year per 100,000). Prevalence is the total number of existing cases at a point in time. Incidence measures risk; prevalence measures burden. A disease can have low incidence and high prevalence if people live with it for a long time (hypertension) or high incidence and low prevalence if it resolves quickly (the common cold).

Morbidity data come from hospital records, physician billings, disease registries, and population surveys like the Canadian Community Health Survey (CCHS). Survey-based self-report is cheap and wide but noisy — people forget, minimize, or exaggerate — while registry data are more precise but limited to what gets diagnosed and coded.

Composite measures try to combine mortality and morbidity into a single number. Two dominate the field:

DALYs — Disability-Adjusted Life Years — measure disease burden as the sum of years of life lost to premature death (YLL) plus years lived with disability (YLD), where disability is weighted from 0 (perfect health) to 1 (dead). One DALY is one lost year of healthy life. DALYs let you compare very different diseases — cancer versus depression, road injury versus migraine — on a common scale. They are the engine of the Global Burden of Disease Study, run out of the Institute for Health Metrics and Evaluation (IHME), which produces regular disease-burden estimates for every country.

HALEs — Health-Adjusted Life Expectancy (or Health-Adjusted Life Years) — adjust life expectancy by the quality of health during those years. Canadian HALE is several years below life expectancy: those last years of life are often lived with disability. HALE captures the goal of “adding life to years” rather than only “years to life.”

QALYs — Quality-Adjusted Life Years — are similar to DALYs in spirit but are used mainly in economic evaluation to compare the cost-effectiveness of interventions. A treatment that adds five QALYs is worth more than one that adds two, and cost per QALY is a common yardstick for public funding decisions.

Every composite measure embeds value judgments. DALYs’ disability weights were derived from panels of experts and respondents and do not necessarily reflect how people with disabilities evaluate their own lives. QALYs can undervalue interventions that help people who already have poor baseline health. No single number captures health; the choice of metric is part of the politics of priority-setting.

5. Epidemiology — The Basic Tool Kit

Epidemiology is the study of the distribution and determinants of health states in populations. It is the basic science of public health and the toolkit you use to make sense of health claims, whether in academic papers or newspaper headlines.

Epidemiological thinking starts with rates, not counts. “There were 5,000 new cancer cases” tells you almost nothing. “There were 5,000 new cancer cases in a population of 1 million aged 50–69, compared with 8,000 in a similar population a decade ago” is a claim you can actually evaluate. Denominators matter.

Risk is the probability that an individual will develop a disease in a defined period. Relative risk (RR) compares risk between groups: smokers have an RR of about 15–20 for lung cancer compared with never-smokers. RR tells you strength of association. Absolute risk difference tells you public-health impact. Suppose an exposure triples a risk from 1 in 10,000 to 3 in 10,000 — the RR of 3 sounds alarming, but the absolute difference is 2 per 10,000. Be suspicious of papers that report relative risks without absolute numbers.

Odds ratios are used in case-control studies and approximate RR when the disease is rare. They are familiar but often misread in the popular press.

The core study designs to know:

• Cross-sectional studies take a snapshot of exposure and outcome at one point in time. They are fast and cheap and are good for estimating prevalence but cannot establish which came first.
• Case-control studies start with people who have the disease and compare their past exposures with those of people who do not. Efficient for rare diseases; vulnerable to recall bias and selection bias.
• Cohort studies follow exposed and unexposed groups forward in time and compare incidence. They establish temporal order and allow estimation of RR. The Framingham Heart Study, the Nurses’ Health Study, and the Canadian Longitudinal Study on Aging are landmark examples.
• Randomized controlled trials (RCTs) assign people at random to an exposure or intervention. Randomization balances confounders on average, giving the cleanest causal inference. RCTs are the gold standard for clinical treatments but cannot be used for many public-health questions (you cannot randomize people to poverty or to smoking).
• Systematic reviews and meta-analyses pool results across studies. A well-conducted meta-analysis with a pre-registered protocol and careful attention to bias is often stronger evidence than any single study.

Confounding occurs when a third variable is associated with both exposure and outcome and distorts the apparent relationship — classically, coffee looks like it causes cancer until you notice coffee drinkers smoke more, and the cancer is due to tobacco. Bias is systematic error in measurement or selection (recall bias, selection bias, publication bias, measurement bias). Chance is random error. A good epidemiological paper walks the reader through all three.

Bradford Hill’s criteria — strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, analogy — are not a checklist for causation but a set of considerations that, taken together, support or weaken a causal claim. Temporality (cause precedes effect) is the one non-negotiable.

Two ideas beginners often miss. First, ecological fallacy: patterns that hold at the population level do not always hold at the individual level. Countries with higher average fat intake have higher heart disease rates; that does not prove that, within a country, individuals who eat more fat have more heart disease. Second, regression to the mean: extreme measurements tend to be followed by less extreme ones, so any “intervention” applied to people with unusually high values will look effective even if it does nothing.

6. Historical Transitions in Health and Disease

In 1971, the Egyptian-American epidemiologist Abdel Omran published a now-classic paper titled “The Epidemiologic Transition: A Theory of the Epidemiology of Population Change.” Omran argued that modernizing populations pass through three stages. In the age of pestilence and famine, mortality is high and fluctuating, life expectancy is 20–40, and infectious disease and undernutrition dominate. In the age of receding pandemics, mortality declines (especially in children), life expectancy rises into the 30s–50s, and epidemics become less devastating. In the age of degenerative and human-made diseases, mortality stabilizes at low levels, life expectancy climbs into the 60s and 70s, and chronic diseases — cardiovascular disease, cancer, stroke — become the leading causes of death. Later scholars added a fourth stage, the age of delayed degenerative diseases, in which people still die of chronic disease but at older and older ages, and a fifth, a potential age of re-emerging infections and health inequities.

Omran’s model was a synthesis of observations most people already knew, but its power was to link three shifts at once — demographic (more survival), epidemiological (different disease mix), and socio-economic (development, urbanization, public health). The transition is not automatic and not uniform: different countries move through the stages at different speeds, and some populations within a country can be in a different stage than others (Indigenous communities in Canada, for example, have a disease burden pattern that does not match that of the non-Indigenous Canadian majority).

The causes of the great mortality decline of the nineteenth and twentieth centuries are contested. Thomas McKeown famously argued that medicine got most of the credit but deserved little of it — most of the decline, he argued, happened before effective medical treatments existed and was driven by rising standards of living, especially nutrition. Others argue that public health measures — clean water, sewage systems, food safety regulation, tuberculosis sanatoria, maternal and infant health programs, vaccination — did more than McKeown allowed. The honest answer is that rising incomes, better nutrition, sanitation, public health, and eventually medical care all contributed, with their relative weights shifting across decades and places. Canada’s own mortality history tracks the international pattern: a sharp decline in infant mortality from 1900 to 1970, the near-elimination of childhood infectious diseases through vaccination, and the slower, steadier gains in adult life expectancy that came from falling cardiovascular mortality after the 1970s.

Two parallel transitions are worth naming. The demographic transition is the move from high birth rates and high death rates to low birth rates and low death rates, passing through an intermediate stage of rapid population growth when deaths have fallen but births have not yet followed. Canada completed this transition decades ago; many low- and middle-income countries are still in its middle phase. The nutrition transition, described by Barry Popkin, traces shifts in diet from traditional, plant-based, labour-intensive food systems to diets high in refined carbohydrates, sugar, processed fats, and animal products — and the concurrent shift from physically demanding work to sedentary lifestyles. The nutrition transition helps explain the global rise in obesity, type 2 diabetes, and cardiovascular disease, including in countries that still have significant infectious-disease burdens, producing a double burden of disease.

7. Leading Causes of Death and Disability

According to Statistics Canada and the Public Health Agency of Canada, the leading causes of death in Canada have been, for most of the last decade, cancer (about 27% of deaths), heart disease (about 19%), COVID-19 during the pandemic years, accidents (unintentional injuries), stroke, chronic lower respiratory diseases, diabetes, Alzheimer’s disease, influenza and pneumonia, and suicide. The precise ordering varies year to year, but the top ten account for roughly three-quarters of all deaths.

Cancer and cardiovascular disease together still dominate, but their trajectories differ. Cardiovascular mortality has fallen substantially over fifty years — a genuine public health success driven by lower smoking rates, better blood pressure and cholesterol control, and improved acute care. Cancer mortality has declined more slowly; incidence continues to rise with an aging population, but improvements in screening and treatment mean survival has improved for many cancers.

Disability burden tells a different story from mortality. DALY-based analyses from the Global Burden of Disease Study consistently show that the leading contributors to disability in Canada are low back and neck pain, depressive disorders, anxiety disorders, migraine, sense-organ diseases (especially hearing loss), and musculoskeletal conditions. These rarely kill but consume enormous quantities of healthy life years. A mortality-only view of the nation’s health would miss most of the burden mental illness imposes and almost all of the burden of musculoskeletal pain.

The leading risk factors — things that raise the risk of many causes of death and disability at once — are, in rough order: tobacco, dietary risks, high blood pressure, high body-mass index, alcohol use, high fasting plasma glucose, low physical activity, high LDL cholesterol, and air pollution. Each of these is amenable to some combination of individual, clinical, and policy intervention.

Unintentional injury is the leading cause of death in young adults. Road traffic, poisoning (including opioid overdose), falls, and drowning dominate. The opioid crisis has reshaped injury mortality in Canada over the past decade: in 2023, opioid toxicity deaths were several thousand per year, concentrated in British Columbia, Alberta, and Ontario, and claimed many young adults who would otherwise have lived decades. The rise is driven by fentanyl contamination of the illicit drug supply, poorly served by a healthcare system that was built around managing chronic disease.

Suicide accounts for about 4,000 deaths per year in Canada, with rates highest in middle-aged men, Indigenous populations (especially Inuit youth in certain communities), and people with severe mental illness. Suicide prevention is a public health priority that sits uneasily at the intersection of mental health care, firearms policy, and economic and social conditions.

8. The Life Course Perspective

The life course perspective argues that health at any age is the product of exposures, experiences, and adaptations accumulated across the whole life, with some periods of development being more sensitive to damage or protection than others. It rejects the idea that adult disease is simply the result of adult behaviour. It also rejects the idea that an unfavourable start dooms a life — it emphasizes trajectories, not destinies.

Several concepts make the framework operational. Critical or sensitive periods are windows when an exposure has outsized effects — fetal development, early childhood, puberty. Prenatal malnutrition, famously studied in the aftermath of the Dutch Hunger Winter, produces increased risk of adult metabolic disease; adverse childhood experiences predict adult depression, substance use, and cardiovascular disease. Cumulative risk is the idea that exposures add up — years of poverty, years of shift work, years of neighbourhood violence compound into differences in health in midlife. Pathway effects describe how early events shape later trajectories: a child born into poverty is more likely to leave school early, which affects employment, which affects income, which affects health. Chains of risk and latency effects capture the observation that some exposures act immediately while others lie dormant and emerge decades later.

Canadian research on the life course is strong. Clyde Hertzman’s work showed that the gradient in children’s developmental outcomes in kindergarten (measured by the Early Development Instrument) predicts later health and economic outcomes with striking precision. The Canadian Longitudinal Study on Aging follows tens of thousands of Canadians aged 45 to 85 and is producing a rich picture of how midlife conditions shape older-age health. Life-course thinking is the intellectual backbone of arguments for investing in early childhood education, paid parental leave, and child benefits on health grounds — each of these is, from a life-course perspective, a form of primary prevention for adult disease.

9. The Canadian Healthcare System

The Canada Health Act (1984) is the federal law establishing the conditions provinces must meet to receive federal health transfer payments. It does not run the system. Delivery is a provincial responsibility under the Constitution, meaning there are thirteen healthcare systems held in rough alignment by the Act’s principles.

The Act’s five principles are public administration (run by a public authority on a non-profit basis), comprehensiveness (covers all medically necessary hospital and physician services), universality (all insured residents entitled to the same level of care), portability (coverage travels across the country), and accessibility (reasonable access without financial barriers, including a prohibition on user charges and extra-billing).

The system is often called “single-payer,” but “single-insurer for hospital and doctor services” is more accurate. Provincial plans pay for physician and hospital care. They do not pay, or pay only partially, for prescription drugs outside hospital, dental care, vision care, psychotherapy, physiotherapy, home care, or long-term care. These gaps are filled — unevenly — by private insurance, out-of-pocket spending, and provincial programs. What “universal healthcare” covers in Canada is narrower than many realize.

Strengths include equitable access to hospital and physician care regardless of ability to pay, relatively efficient administrative overhead compared with multi-payer systems, and outcomes comparable to peer countries while being less expensive than the United States.

Weaknesses are well-documented. Primary care is stretched; millions of Canadians lack a family doctor. Wait times for specialists and elective surgery are long by international standards. Canada is one of the few high-income countries with universal medical insurance but no universal pharmacare. Long-term care was exposed during COVID-19 as poorly resourced. Mental health care outside hospitals is often accessible only to those with private means or workplace benefits. Indigenous health falls through federal-provincial jurisdictional cracks.

Health spending is about 12% of GDP, with roughly 70% from public sources. CIHI publishes annual reports on spending. Hospitals and physicians account for about half, drugs are next, and long-term care is growing fastest. Models of care are shifting toward team-based primary care and virtual care, unevenly across provinces.

10. Health Promotion and Behaviour Change

Health promotion is the process of enabling people and communities to increase control over and improve their health. The Ottawa Charter for Health Promotion, adopted at a 1986 WHO conference hosted in Canada, is the field’s foundational document. It sets out five action areas: build healthy public policy, create supportive environments, strengthen community action, develop personal skills, and reorient health services toward prevention. The charter was a deliberate rejection of a purely behavioural, individual-education model; it insisted that health is produced by conditions as much as by choices.

Within that broad frame, a large literature on behaviour change tries to answer the harder downstream question: given that a person wants to eat better, quit smoking, exercise more, or manage a chronic condition, how can clinicians and programs help them do it? A few widely used models:

• The Health Belief Model proposes that behaviour change follows from perceived susceptibility to a threat, perceived severity, perceived benefits of action, and perceived barriers, plus cues to action and self-efficacy. It explains why information alone often fails — if people do not feel susceptible, or the barriers loom large, knowledge does not translate to action.
• The Transtheoretical Model (Stages of Change), developed by Prochaska and DiClemente, describes change as passing through precontemplation, contemplation, preparation, action, maintenance, and (often) relapse. Its clinical value is in matching interventions to the stage a person is in.
• Social Cognitive Theory (Bandura) centres self-efficacy — the belief that one can successfully perform a behaviour — as the key mediator of change. Self-efficacy grows from mastery experiences, vicarious learning, social persuasion, and managing emotional and physical states.
• The Theory of Planned Behaviour (Ajzen) predicts behaviour from intentions, which are shaped by attitudes, subjective norms, and perceived behavioural control.
• Motivational interviewing, developed by William Miller and Stephen Rollnick, is a clinical counselling style that elicits a person’s own reasons for change rather than arguing for change from the outside. It has evidence for effectiveness in substance use, medication adherence, and lifestyle behaviours.

A more recent frame, from behavioural economics, is the nudge — structuring choice environments so the default option is the healthier one, without removing alternatives. Auto-enrolment in organ donation, placement of healthier foods at eye level, and making physical activity the path of least resistance are examples.

None of these models is a silver bullet, and behaviour change at the individual level is notoriously hard to sustain. This is one reason public health scholars emphasize structural interventions — changing prices, regulations, and built environments — alongside interventions aimed at individuals. Smoking rates in Canada fell over decades through a combination of taxation, advertising bans, smoke-free legislation, product regulation, cessation programs, and sustained counter-advertising. Any one of these would have been insufficient; the combination worked.

11. Chronic and Non-Communicable Diseases

Chronic or non-communicable diseases (NCDs) are conditions of long duration and slow progression. The big four globally are cardiovascular disease, cancer, chronic respiratory disease, and diabetes, causing about seven in ten deaths worldwide and a similar share in Canada.

Cardiovascular disease — heart attacks, strokes, heart failure — remains the second leading cause of death in Canada. Modifiable risk factors are tobacco, hypertension, dyslipidemia, diabetes, obesity, physical inactivity, poor diet, and excess alcohol, with contributions from air pollution, shift work, chronic stress, and sleep disorders. Falling CVD mortality over fifty years is one of medicine’s great successes, though progress has slowed.

Cancer is not one disease but hundreds. The most commonly diagnosed in Canada are lung, breast, colorectal, and prostate; lung cancer kills the most because it is diagnosed late. Tobacco drives lung and several other cancers; alcohol is a category 1 carcinogen implicated in breast, colon, head-and-neck, liver, and esophageal cancers. Screening programs (cervical, breast, colorectal) reduce mortality but have their own harms from false positives and overdiagnosis.

Chronic respiratory disease — COPD, asthma — is driven heavily by smoking and air exposures. Type 2 diabetes prevalence has roughly doubled in a generation, with higher rates in South Asian, Indigenous, and African-Canadian populations; it tracks the nutrition transition and raises cardiovascular risk substantially.

Chronic disease management has shifted toward ongoing self-management, multidisciplinary teams, and the Chronic Care Model. But the biggest lever remains upstream prevention: tobacco control, food-environment regulation, active transportation, and cleaner air have larger population effects than any clinical intervention.

12. Infectious Disease and Public Health

It is tempting in wealthy countries to treat infectious disease as solved. COVID-19 was a reminder that it is not. Infectious disease remains central for four reasons.

First, new pathogens emerge: SARS (2003), H1N1 (2009), MERS (2012), Ebola, Zika, SARS-CoV-2. Animal spillover, global travel, urbanization, and land-use change make new pathogens more likely, not less. Second, old pathogens resist control: TB, malaria, and HIV remain global killers, and in Canada, TB rates in some Inuit communities are among the highest in the world — a direct product of overcrowded housing and historical injustice. Antimicrobial resistance threatens to partially undo the antibiotic revolution. Third, vaccination gains are fragile: measles returns when coverage falls. Fourth, infectious disease interacts with chronic disease: influenza and pneumonia kill mainly people with underlying conditions; hepatitis B and C cause liver cancer; HPV causes cervical cancer and is now vaccine-preventable.

Public health infrastructure holds infectious disease in check: surveillance, vaccination programs, infection control in hospitals and long-term care, contact tracing, and environmental regulation of water and food. These functions are invisible when they work — until stress-tested, as during COVID-19, when the cost of underinvestment becomes visible. The pandemic also exposed inequities: exposure, severe illness, and death were concentrated among essential workers, racialized and low-income neighbourhoods, long-term care residents, and people with pre-existing conditions. A pandemic is an unequal event, and its unequal impact is a social-determinants story.

13. Mental Health — A Public Health Perspective

Mental illness contributes an enormous share of disability in Canada. Depression, anxiety disorders, substance use disorders, and bipolar and psychotic disorders together account for a significant fraction of total DALYs. About one in five Canadians experiences a mental illness in any given year, and roughly half will at some point in their lives.

The public health approach to mental health is broader than psychiatry. It includes promotion of mental well-being (social connection, meaningful work, physical activity, sleep), prevention where risk factors are known (childhood adversity, trauma, substance use), early intervention (youth programs, postpartum screening), treatment, and recovery-oriented care (employment, housing, inclusion). Clinical care matters, but so do upstream conditions.

Access is uneven. Evidence-based psychotherapy (CBT, interpersonal therapy, DBT) is generally not covered by provincial insurance unless delivered by a physician. Canadians pay privately, rely on workplace benefits, wait months, or go without. Some provinces now fund structured CBT programs, but coverage gaps remain a major hole in the universality of Canadian health care.

Substance use sits at the boundary of mental health and public health. Harm reduction — supervised consumption sites, opioid agonist therapy, drug checking, safer supply — is evidence-based and, where implemented, associated with reduced overdose and blood-borne infection. It is politically contested because it asks people to accept that ongoing drug use is a reality to be managed rather than a failure to be punished. Stigma remains a barrier: people with mental illness are more likely to avoid treatment, less likely to be hired, and more likely to experience poverty and homelessness.

14. Environment and Health

Human health is embedded in environmental systems — the built environment (roads, parks, housing density, walkability), the natural environment (air, water, soil, climate), and the food environment.

Air pollution is the largest environmental health risk factor globally. In Canada, ambient PM2.5, ground-level ozone, and smoke from wood stoves and wildfires contribute thousands of premature deaths per year. The 2023 wildfire season — the worst in Canadian history — pushed air-quality indices to hazardous levels across much of the country, and such events are projected to become more frequent. Water is a Canadian success story except where it is not: most Canadians drink safe water, but dozens of First Nations communities have lived under long-term drinking water advisories.

Climate change is now recognized by major medical journals as the defining public health challenge of the twenty-first century. Mechanisms include direct heat effects (heatwaves kill disproportionately older, poor, and isolated people in Canadian cities), wildfire smoke, vector-borne disease expansion (Lyme disease moving north as tick ranges expand), food and water insecurity, and mental health impacts from disaster and displacement. Mitigation is preventive public health at planetary scale, with co-benefits from active transportation, plant-forward diets, and cleaner energy.

Built environment research shows walkable, mixed-use neighbourhoods with parks and transit support physical activity, social connection, and mental health; car-dependent suburbs are associated with sedentary behaviour, obesity, and cardiovascular disease. Urban planning is public health. Occupational exposures — dusts, chemicals, noise, shift work, job strain, violence — account for a substantial share of chronic disease and injury, and fall disproportionately on workers with less bargaining power.

15. Reading Health Literature Critically

A major goal of a first course in health is to make students better consumers of health information.

Primary sources are original research — peer-reviewed articles reporting data. Secondary sources are reviews, meta-analyses, and clinical guidelines. Tertiary sources are news coverage and popular articles. A newspaper article citing “a new study” is tertiary, and the study may be small, preliminary, or misinterpreted.

A checklist for a primary research paper: Who funded it? (Sponsored studies find more favourable results for sponsors’ products.) What was the research question, and does it match the press release? What was the study design, and what are its characteristic weaknesses? Who were the participants, and does the sample generalize? What was measured — are the outcomes surrogate (cholesterol) or patient-relevant (heart attacks)? Are effect sizes reported in both relative and absolute terms with confidence intervals? What limitations does the paper acknowledge? And does the discussion match the data, or is it hyped?

Beyond individual papers, know about publication bias (null results get published less), p-hacking (running many analyses until one is significant), pre-registration, and the replication crisis. Be suspicious of single dramatic findings and of nutritional claims that change direction every few years.

Use trustworthy secondary sources. Cochrane reviews provide rigorous meta-analyses. The Canadian Task Force on Preventive Health Care and USPSTF issue evidence-based recommendations. PubMed is the database to search. The GRADE framework gives vocabulary for thinking about evidence quality.

Finally, absolute claims are rarer than we think. The appropriate response to uncertainty is calibrated, not dismissive. “We don’t know exactly, but the best current evidence suggests…” is more honest than either “studies have proven” or “there is no evidence.”

16. Health Equity and Policy

Health equity is the absence of avoidable, unfair differences in health between groups. Not every health difference is inequitable — 80-year-olds have more heart disease than 20-year-olds, and we do not consider that unjust — but differences produced by unfair social arrangements are. Whitehead’s classic formulation is that health inequities are differences that are avoidable, unnecessary, and unfair.

The distinction between equality (the same for everyone) and equity (what each person needs to reach the same opportunity for health) is worth internalizing. Giving every student identical school lunches is equal; giving food-insecure students extra support so they arrive at school ready to learn is equitable. Equity-oriented policy means paying more attention to people with greater need, not identical attention to everyone.

Healthy public policy is the term for policies across sectors that are assessed for their impact on health. A transportation policy, a housing policy, a minimum wage, a tax code — each of these is a health policy whether or not it is labelled one. Health in All Policies is an approach, endorsed by the WHO and adopted in varying degrees by Canadian governments, that asks policy-makers in every sector to assess the health implications of their decisions.

Specific policy levers with demonstrated health effects include: tobacco control (tax, advertising bans, plain packaging, smoke-free laws), alcohol control (minimum pricing, outlet density, availability), food policy (front-of-pack labelling, trans-fat bans, sugar-sweetened beverage taxes, school food programs), housing policy (subsidies, rent control, homelessness reduction), income policy (minimum wages, child benefits, guaranteed income pilots like Ontario’s interrupted experiment), early childhood education and care, road safety (speed limits, drunk-driving enforcement, vehicle standards), and environmental regulation (clean air and water standards, climate policy).

Two themes deserve emphasis in closing.

First, most of the work of public health is invisible when it is working. You do not thank the water treatment plant for not giving you cholera; you do not thank the tobacco taxes for the heart attack you did not have. The benefits of upstream interventions are large but diffuse, making them politically fragile. One of the responsibilities of people who study health is to make the invisible visible.

Second, health is not only an individual achievement. It is something populations produce together, through the institutions they build, the policies they pass, and the conditions they maintain for one another. A person’s probability of being healthy at 70 is shaped by things their parents could not control, things their government decided before they were born, and things the society around them is willing to pay for today. That is why an introductory health course is, in the end, a course in how to think about what we owe one another.

These ideas — the widened definition of health, the determinants framework, epidemiological literacy, the epidemiologic transition, the structure of the Canadian healthcare system, the difference between downstream and upstream action, and the primacy of equity — are the scaffolding on which the rest of an undergraduate health sciences degree hangs. Everything later, from clinical courses to policy analysis to research methods, sits on top of the vocabulary and mental models introduced here. The details will shift as evidence accumulates; the frameworks tend to last.