Determinants of Health and Health Inequities

Effective disease management requires attending to the patient’s immediate problem, then tackling any modifiable factors that gave rise to the condition – in Peter Sulawesi’s case, his dilapidated and perhaps mouldy living environment. The goal is to avoid a revolving door cycle of repeat symptomatic treatments for the effects of an enduring environmental cause. It is therefore helpful to combine clinicians’ interventions for individual patients with interventions to address determinants at the community and population levels.

Public, and Population Health

Primary care physicians like Dr. Rao work within the acute care system that operates alongside public health and social services systems designed to address contextual factors that exacerbate illnesses such as Peter’s asthma. The public health system focuses on preventing disease and protecting health (See HEALTH PROTECTION in Glossary). “Public health is defined as the organized efforts of society to keep people healthy and prevent injury, illness, and premature death. It is a combination of programs, services, and policies that protect and promote the health of all Canadians.”¹ Unfortunately, this definition does not specify what public health actually does. This is because, unlike other branches of medicine, public health does not address a particular organ system, type of disease or therapeutic approach, but employs a variety of approaches to address whatever health issues are most pressing in each place and time. As patterns of disease evolved historically, the discipline saw a succession of names as it wrestled with whether environmental factors, or individual behaviour, or social problems should form the main target of interventions.

Many public health interventions have been outstandingly successful, most notably in controlling infectious diseases that have an identifiable single link in their causal chain that can be broken, for example by an immunization or by improved sanitation. But recent challenges such as the obesity epidemic prove more intractable: the link between diet and body weight is complex; weight gain can be remarkably hard to reverse and strong social forces promote inappropriate diets. We need interventions on several levels: individual counselling, creation of supportive environments and broad policy changes to modify the affordability of healthy foods. Coordinated interventions of this scope are the hallmark of the population health approach. This holds that, while encouraging individual responsibility for health, we must also address underlying social determinants, such as poverty, that constrain people’s ability to achieve real gains in health.

The concept of population health gained prominence in the 1990s. It overlaps with public health. Both are concerned with patterns of health and illness in groups of people rather than in individuals; both monitor health trends, examine their determinants, propose interventions at the population level to protect and promote health; both propose ways to deliver these interventions. The distinction is subtle, but the population health approach is seen as broader, as forming a unifying paradigm that links disciplines from the biological to the sociological. It proposes a rational basis for allocating health resources that balances health protection and promotion with illness prevention and treatment, while also making a significant contribution to basic science.² Dr. Christina Mills, past president of the Canadian Public Health Association, quipped “Population health is how we think, public health is what we do” (quoted by Hancock³). A public health approach to tackling childhood obesity might design education programs for parents and children, advocate for subsidizing healthy school lunches, propose tougher regulations on marketing junk food to children, and promote physical activity, for example. A population health approach might extend these approaches to analyze the food system itself: how do agricultural policies affect the price of food and how could they be changed? Could city planning policies overcome the problem of urban food deserts where people without a car lack access to a grocery store? Population health still values personal health as a key outcome, but views issues from a broader perspective that includes economics, environmental sustainability, social justice, etc.

Although physicians treat individual patients, they should be aware of the population perspective for several reasons. First, the old chestnut that “common things occur commonly” is true: your patient’s condition is a symptom of health patterns in the population, so knowing the population prevalence will influence the hierarchy of your differential diagnosis. Chest pain in a 50-year-old is more likely to be of cardiac origin than the same complaint in a 15-year-old. Second, a patient’s lifestyle may have caused his medical condition, but the driving forces for this lifestyle lie in his social circumstances. Your efforts to help him change health behaviours will often be frustrated by the social pressures he experiences. It may be more efficient to tackle a disease at the population level (e.g., by lobbying for taxation on high-fat foods and using the proceeds to subsidize fruits or exercise programs) than by treating large numbers of individuals (see Chapter 8).

Reflecting a population health approach, the CanMEDS physician roles include health advocacy: “As Health Advocates, physicians responsibly use their expertise and influence to advance the health and well-being of individual patients, communities, and populations”.⁸

In general, public health is mandated to focus on the physical environment, including chemical or biological exposures that may exacerbate Peter’s condition. This seems ineffectual in this case. The population health perspective views Peter’s asthma as an example of a broader pattern of remediable health inequalities between social groups. Might this offer a route to improvement?

Health Inequalities

In every society there are variations in health, whether between individuals, groups of people, regions or between countries.⁹  Indeed, most diseases and health states occur in predictable patterns. As an illustration, Figure 2.1 shows life expectancy in Canada plotted by sex and income.^{10, 11} The data were taken from a study of 2,734,800 Canadians who were followed for 15 years after the 1991 census. Deaths during that time were linked back to the income information recorded on the 1991 census. Income was adjusted according to the size of the family that depended on it, to give a better indicator of income adequacy. The result is shown grouped into five categories or quintiles of income, running from poor (coded as 1) to rich (coded as 5). The vertical bars show the years of life remaining, on average, to a 25-year-old person in each sex and income category.

The results show troubling disparities in health: men in the poorest category can expect to live about 7 years less than those in the richest category (48 versus 55 years beyond age 25); for women the contrast is about 5 years. Moreover, the deficit is not only for those with the lowest income: there is a steady rise or gradient in longevity across income levels and this is called the “social gradient in health”.

This chart shows life expectancy, but rates of disability and ill-health also rise as socioeconomic status declines: poorer people experience the double deficit of a shorter life and a less healthy one. Such patterns are attributed to “social determinants” of health, defined as “the circumstances in which people are born, grow up, live, work and age.”¹² Health gradients also occur across levels of education, occupation and residential area, all of which reflect socio-economic status as a social determinant of health. But note that the word “determinant” is not intended to imply inevitability or determinism; it comes from the Latin de termine, or “from the end” (i.e., the origin) of a chain of causal influences.

Systematic variations such as those in Figure 2.1 should in principle be correctable: if richer people can live longer, there seems no inherent reason why poorer people could not live equally as long. A disadvantage that is correctable or could have been avoided is termed a HEALTH INEQUITY, carrying the idea of unfairness and moral unacceptability. Accordingly, the reduction of social inequities in health has become a central goal of population health policy.¹² “Reducing health inequities is an ethical imperative. Social injustice is killing people on a grand scale…  The conditions in which people live and die are shaped by political, social, and economic forces.”¹² A leading example of health inequity in Canada is the health of Indigenous peoples, as shown in the box.¹¹

Health inequities derive ultimately from many historical and social determinants. But social inequities per se can also play a causal role. For example, power inequities between the genders in some African countries exacerbate the risk of HIV infections among women because they are prevented from using protection or are forced into prostitution. Or, a person’s mental health may suffer because they perceive the unfairness of continued social exclusion. The following sections will review some of the main social determinants of health, and then review analyses of how these interact to damage health.

The Major Social Determinants of Health

Virtually any characteristic of a society can affect the health of its citizens, so might be considered a social determinant of health. To make this less daunting, agencies such as Health Canada and the WHO have identified key social determinants that deserve special attention (see the additional materials box). The following paragraphs summarize the impact of a selection of determinants from Health Canada’s list.

Early childhood development

In treating a disease, a doctor intervenes to correct a process that often began many years earlier. The life course perspective extends the origins of a disease back to childhood, and even to exposures faced by a person’s parents.^{17, 18} Nutrition and stimulation in early life influence physical and emotional development and these, if positive, build resiliency; if negative, they enhance vulnerability. Timing of exposures and experiences is also critical. For example, traumatic experiences in early childhood shape personality and have a lasting impact on how a person views his world, how he relates to others, and how he interprets events. The impact of broken homes, chronic childhood stresses and so forth have non-specific effects, acting mainly to increase emotional vulnerability in adult life.¹⁹ The recognition of critical periods in early child development has led to the popularity of programs such as Head Start.

Income and social status

While Health Canada’s list of determinants combines income and social status, it may be helpful to unpack these. Social status includes both a person’s formal position in society (student, manager, retiree) and the subjective feelings of prestige that their position accords them. The latter may be relevant in understanding mental health, whereas for conditions such as an occupational injury the person’s social position may be the most relevant. Social status is partly inherited, but is largely achieved through education and thence occupation. It is also influenced (and to varying extents) by factors such as ethnicity, personality, and happenstance. Linked to all of these is a level of wealth, which affects the person’s range of lifestyle options.

It is virtually impossible to separate the health effects of each of these factors: in epidemiological terms, an example of CONFOUNDING. Ultimately, it may not matter: whatever marker of social status and whatever health indicator is used, there is a universal tendency for those in higher social positions to enjoy better health. Exceptions are rare and often reflect the working of other factors: for example, elevated breast cancer rates among higher income women probably occur not because of wealth but due to delayed first pregnancy linked to establishing a career. Some other examples of an inverse gradient are transient and reflect social change. An example occurred in the 1930s, when heart disease was increasing and cases often occurred in richer people who could afford a cardiogenic diet and sedentary lifestyle. Subsequently, the decline in heart disease has occurred more steeply among richer and better-informed people so that the familiar inverse income gradient now holds.²⁰

Income−especially insufficient income–may be described in relative or absolute terms, and can apply to individuals and to society as a whole (gross national income). Absolute poverty refers to lacking the resources to meet basic needs for shelter, nutritious food, clothing, and education; a poor person cannot afford choices that promote good health. In low-income countries, their absolute poverty and the resulting lack of infrastructure form the fundamental health determinant. In the initial stages of economic development population health status improves rapidly as national income rises up to the stage where basic necessities (food and shelter) are available to virtually all (see the “International disparities in health” box). Beyond that point, however, further rises in national wealth have less effect on improving health. Instead, overall health in richer nations is influenced more by the evenness of distribution of income within society, or income inequality: a marker of the range of incomes across the different levels of society.

International disparities in health

As of 2017, Canadians could expect to live almost 82 years on average, similar to Australia, France and Spain. Citizens of Japan and Singapore outlive us, while Americans had a life expectancy of 79 years on average, placing them in 53rd place in one international ranking (http://www.geoba.se/population.php?pc=world&type=15). The disparities between nations are striking: women in Japan live 85 years on average, more than 40 years longer than women in Sierra Leone, Botswana or Swaziland.

Among the poorest countries, longevity increases rapidly with growing national wealth, as illustrated in the figure below. However, beyond a Gross National Income of around $20,000 US per year, gains in life expectancy flatten and further improvements appear to derive more from the way that incomes are distributed within societies than from increasing the overall GNI. This was beautifully described in a brief video by Hans Rosling: http://www.youtube.com/watch?v=jbkSRLYSojo

Sources: Life expectancy Wikipedia
World Bank: Gross national income per person

Discussion Point: How could you explain the pattern shown in the graph in your own words?

What are the mechanisms for this? In every society there are rich and poor, and the richer have better health (Figure 2.1). As overall wealth improves, so does health, but richer groups reach a ceiling above which more wealth cannot further improve their health. Meanwhile, poorer people lag behind in health, pulling the average down, so redistributing wealth to them would raise the average health more efficiently than across-the-board increases. Hence in richer countries, the relative size and disadvantage of the poorer segment of the population (i.e., the extent of income inequality) becomes a better predictor of overall health than total national income; countries that redistribute wealth via fiscal policies to poorer people tend to have better overall health. This association between relative poverty and health is now termed income inequality in health (see HEALTH INEQUALITY in Glossary) and has been widely discussed.^{9, 16, 23-25}

At the level of treating individual patients like Paul Richards (whom we met in Chapter 1) there may be local agencies to assist the clinician – see the following boxes.

Education and health literacy

Education both results from, and contributes to social position. The social position of a child’s parents influences her access to educational opportunities. The resulting education influences employment opportunities and thereby income, and influences whom she meets and where she lives. All of these indirectly influence health; dementia offers an example. Here, a lack of education may lead to careers that expose the worker to neurotoxic substances that damage brain function. Conversely, higher education, and the stimulating career it may lead to, may build complex neural networks that protect the aging brain.²⁶  Education also affects a person’s ability to navigate the health care system, to interpret health information and to communicate effectively with physicians and other professionals.^{27, 28}  “Health literacy” refers to the patient’s ability to understand health information and to follow guidelines for their treatment. A 2008 Canadian Public Health Association report concluded that only about 55% of Canadian have a level of literacy that enables them to negotiate the health care system effectively, to follow written advice on health care and on their medications.²⁷ Physicians need to bear in mind that our increasingly complex health system places high demands on the reading and problem-solving skills of patients.

Social support networks

Ms. Sulawesi lacks a supportive social network. No-one else here speaks her native language and she feels alone in a strange place. Social connections benefit health in several ways. They offer a source of emotional reassurance that helps a person cope with adversity. Networks can provide information, advice and practical support, such as knowing someone who can assist in a time of need. They can also support people during the process of changing health behaviours. People who have strong social ties, who belong to clubs or organizations, who both give and receive assistance or who volunteer, report feeling healthier than others.²⁹ A TED talk shows how a physician gained insight into the social networks of his patients.

The association between social connections and health also holds at the population level: communities that establish collaborative networks are resilient and better able to address social and economic challenges, so can be seen as more healthy. Social capital refers to a resource that derives from people’s willingness to cooperate and engage in collective action; this willingness in turn reinforces trust and confidence within the network. Neighbourhood watch programmes are an example. By contrast, low social capital is characterized by suspicion and hesitation to collaborate with others; this may occur where there are wide disparities in income and a perception of social inequalities. Various studies have linked higher social capital to reduced all-cause mortality²⁵ and to greater well-being, better care for children, and lower crime.³⁰

Employment, working conditions, and occupational health

The WHO recognizes fair employment and decent work as a cornerstone of health, and advocates for fair minimum wages, full employment, and occupational health and safety standards.¹⁶ Although Canada’s overall unemployment rate may be low, at 6 or 7%, this masks wide variations. There are inequities across regions and across population groups – 11.5% of recent immigrants are unemployed and many more are underemployed.³¹

The health consequences of unemployment have been extensively studied and reveal complex relationships. Overall, people who lose their jobs experience reduced self-perceived health and increased mortality, but the effect varies by age, gender, and education.³² The health impact also varies according to the general unemployment level: where many individuals lose their jobs the health impact appears less severe.³³

Work stress refers to high expectations at work, often accentuated by a worker’s low level of control over their work (see Definitions box). Demands that exceed the person’s coping ability result in feelings of strain, perhaps also in somatic disorders such as hypertension, peptic ulcers, migraine headaches and others. These affect many Canadians, especially women.³⁴ Working conditions may combine with other determinants, such as income, so that the lowest income households typically report higher levels of work stress due to job insecurity and dissatisfaction, exerting adverse effects on physical and mental health.³⁵ Work strain can arise from a combination of high psychological demand (such as being pressured to work fast) while also having little freedom to make decisions affecting the job (e.g., being in a subordinate position).³⁶ Strain also results from a mismatch between work effort and reward: jobs that demand high effort for low gain produce feelings of exploitation that predict poor health.³⁷ A study that followed 10,000 British civil servants over 10 years showed that those who had little control over their work environment had an increased risk of subsequent heart disease.³⁸  Reorganizing the workplace to provide a greater variety of tasks and more decision-making power at work may decrease risk.

Work injuries are an important cause of disability and mortality in Canada. In 2015 there were over 232,000 claims for lost time at work due to injury; 62% of which were for men.³⁹ The lower a worker’s income, the more likely they are to experience a work-related injury.⁴⁰

The physical environment

Environmental influences on health can be positive or negative, and exist at all geographic levels, from global (climate change) to national and regional issues (the destruction of war; air and water pollution), to local issues (Ms. Sulawesi’s mouldy apartment). The positive benefits of spending time in beautiful surroundings are universally celebrated (see box “Positive places”) but most research focuses on negative environmental influences.  Contaminants in air, water, soil and food are associated with both communicable and non-communicable diseases. Climate change and the associated weather extremes increasingly affect public health: hyperthermia from extreme heat; burns from fires; injuries from extremes of wind and rain; social disruption from changing sea level; under-nutrition in poor areas due to the impact on agriculture; increased risk of food-, water- and vector-borne infections; and the changing distribution of vectors and infectious agents which may introduce disease to previously unaffected regions.⁴¹ Few communities will be immune and there are very few short-term solutions. Further information from a Canadian perspective can be found in reports from Natural Resources Canada.^{42, 43}

The active transportation movement is seeking ways to encourage human-powered transportation (walking or bicycling rather than driving) as a way to reduce pollution while promoting physical fitness. Feasibility depends on design of the built environment such as the proximity of relevant destinations, perceived safety, street design, and also the natural setting, with parks or trails.⁴⁸ North American preference for private motor transport remains strong; as people move further from the city centre they drive more, increasing the risk of vehicle collisions, as well as “higher rates of heart and respiratory diseases and obesity, and elevated stress related to both commuting among congested traffic and increased noise levels.”¹⁶ In rural areas where cars are the only means of transport and where walking or cycling is impractical (and often dangerous because of road conditions) the prevalence of obesity is higher than in urban areas, and road traffic injuries are frequent.

Individual and public health services

Innovations in health care have conferred immense benefits on health and longevity, especially for countries of the developed world. Pharmaceuticals, including antibiotics, antisepsis and life-saving surgical procedures have revolutionized the management of most diseases.

But the most impressive impact came from public health interventions such as sanitation and communicable disease control measures, and from disease prevention (immunization, tobacco control measures, and screening).⁴⁹ Basic engineering measures, such as protecting water supplies, improving food production or reducing overcrowding in homes, often have the greatest impact on overall health. This was famously illustrated by the decline in tuberculosis in England and Wales. As Figure 2.2 illustrates, tuberculosis mortality had been declining for at least 100 years before the introduction of any effective therapy; this early decline was achieved by non-specific means such as improved housing and nutrition, and through specific legislative measures such as banning spitting in public to reduce disease transmission. Similar patterns of decline occurred for polio, smallpox, and whooping cough, all of which responded dramatically to improvements in hygiene long before effective medical treatments were developed.

Public health measures to improve air and water quality benefit all citizens, whereas the benefits of individual medical care are less evenly spread. Roughly four million Canadians do not have access to a family physician.⁵⁰ Despite universal insured health care, access to medications, dentistry, home care, and home support can be significantly affected by income. But even when financial barriers to care are removed, we run the risk of continued health inequities if programs are not accessible because of location, or because of a person’s feeling of discomfort at using facilities. Practitioners’ offices tend to be built in richer neighbourhoods, where property values will be preserved and quality of life for their employees is more attractive, but where the need for care is lower. Similarly, facilities relevant to promoting health, such as commercial exercise facilities, are less likely to be built in lower-income or immigrant neighbourhoods.⁵¹ There is an inherent tension between economic efficiencies, which lead to clustering specialized services in urban areas, and geographic access for people in rural areas. The greatest overall benefit for health may now come from improving access to care for disadvantaged groups: distance medicine for people in remote areas; community health centres for street dwellers, sex trade workers and drug addicts; family planning clinics for teenagers; and clinics tailored to multi-ethnic neighbourhoods, with staff members who speak minority languages and deliver culturally appropriate care.

Gender

Sex refers to our biological identity as male or female, whereas gender refers to the differential status, lifestyles and access to services that are linked to a person’s sex. It refers to “the array of socially constructed roles and relationships, personality traits, attitudes, behaviours, values, relative power and influence that society ascribes to the two sexes on a differential basis.”⁵²

Women in contemporary Canada on average live longer than men, as illustrated in Figure 2.1, and yet women experience more morbidity. Biological differences between the sexes, earlier development of fatal conditions such as heart disease among men, along with gender differences in the distribution of other health determinants, contribute to these patterns.⁵³ Nevertheless, several gender inequities remain, and largely as a result of the women’s movement these have received considerable attention. These occur in all societies in terms of differences in power, freedom, resources and values, and these inequities may affect health. The most egregious examples include the exploitation of women in the sex trade, underage marriage, or the work conditions in sweat shops in the garment industry. In developed countries there are often gender inequities in income, such that wages for women may be around 20% lower than those for men.⁵⁴ Because single parents are almost always women, the lower income of women also affects their children.¹⁶

Gender inequities in health do not only result from income disparities; gender is also linked to differential access to health services, to unequal obligations to provide unpaid family care duties, and to disparities in nutrition.²³ Gender inequities also exist in health research: clinical trials historically have been more likely to use male experimental subjects and yet the benefits of many interventions vary between men and women.^{55, 56} For example, mortality due to cardiovascular disease is increasing in women, yet they are under-represented in research studies.⁵⁷ Women present cardiac disease differently than men, and are less likely to be diagnosed accurately and to receive timely treatment. Given these disadvantages of being female, we have yet to fully explain why women live longer. Part of the explanation is gender differences in risk taking, which in turn is linked to culture.

Culture

“Culture is a system of ideas, values, and metaphors that are consciously and unconsciously used or enacted by people in their everyday lives. It is not a rigid set of behaviour traits but a fluid and adaptive system of meaning.”⁵⁸ Culture “explains what one must know and do to function in a given society.”⁵⁹ Some related terms are shown in the definitions box.

Culture filters the effect of other social determinants, influencing how groups of individuals react to their circumstances and environment. Our cultural background influences our beliefs, behaviours, perceptions, emotions, language, diet, body image, and attitudes to illness, pain or misfortune, all of which can influence health and the use of health care.⁶⁰ Culture also underpins values–our deeply held beliefs that define what is desirable and moral–and values influence expectations of behaviour, including the way a doctor’s actions are perceived by the patient. However, although cultures may be shared, people are far from homogeneous, and we must never assume that all members of a culture will hold the same norms and values or will react the same way to new ideas and knowledge. Some errors and prejudices can be avoided by being careful to view culture as influencing behaviour within each specific context, rather than in general.⁶⁰  Chapter 3 explores ways in which clinicians can incorporate cultural awareness into their daily practice of medicine.

Determinants and Risk Factors

The reference to a person’s culture as a filter for other social determinants of health introduces the idea of multiple steps in the chain of disease causation, running from the broadest social determinants through local environmental influences, to personal risk factors. A common metaphor of disease causation (and prevention) distinguishes between underlying or distal factors, such as a government policy on free immunization clinics, intermediate factors such as accessibility of local health care facilities, and proximal factors such as whether an individual chooses to obtain an immunization. An equivalent metaphor refers to upstream and downstream factors (see Illustrations box).

Social determinants establish the broad patterns of health in groups or populations: they set the incidence rates of disease, but they do not identify which individuals will get sick. There will always be variability around the averages shown in a chart such as Figure 2.1: some individuals live longer than the average of their income group and others live less long. This variability within a group is most helpfully attributed to the balance of personal risk and protective factors – characteristics of the person, their biology, behaviour, or environment that combine to increase or reduce their risk compared to that of the group. To explain an individual case we have to consider both the underlying determinants of disease incidence in the population that set the baseline risk for the group of which he or she is a member, as well as the individual risk factors that modify the base-rate for this individual, relative to the absolute risk in the group.

We may now extend the diagram of the NATURAL HISTORY of a disease, introduced in Chapter 1, to show a chain of causation as illustrated in Figure 2.4. The chain is laid out over the lifetime of an individual:¹⁸

Although the terminology is inconsistent among authors, it may make sense to refer to an influence such as socio-economic status as risk factor when referring to an individual (Paul’s limited income has forced him to rely on collecting wood for heat; the physical effort increases his risk of a cardiac event) and as a determinant when the focus is on group processes (the general rise in the price of heating oil hits poorer families especially hard). Paul’s smoking is a risk factor but it was to some extent influenced by the pattern of smoking in the social group in which he lives – the group culture. That pattern developed in the context of social determinants such as national policies governing tobacco; these policies in turn had economic and historical roots. As most of the modifiable risk factors concern individual behaviour, the following sections review explanatory models for health behaviours.

Personal health behaviours and coping skills

Many upstream social determinants influence health via personal behaviours, most notably smoking, diet and exercise patterns. Health behaviour refers to actions that influence whether or not a person will become ill; illness behaviour refers to his reactions when he does, including whether or not he seeks care, then follows the doctor’s recommendations. Illness behaviour is influenced by social expectations, described by sociologists in terms of the “sick role”, which refers to society’s expectations for a person who is ill. Society permits the sick person to be exempt from his normal social roles but in return he is expected to try to regain health, partly by seeking competent medical care and following the doctor’s recommendations, including modifying health behaviours.^{61, 62}

Clinicians generally find that altering a patient’s health behaviour is slow and difficult. In part this is because health behaviours are not solely a matter of personal choice, but are strongly influenced by social and cultural pressures so that change is most likely to result from changing social determinants (see box “Changing personal health practices”). Psychology offers several theoretical models that describe the personal and contextual influences on health behaviour; these help explain why behaviour is often so hard to change. One of the earliest and best known is the Health Belief Model.

The Health Belief Model

The Health Belief Model (HBM) was proposed by G.M. Hochbaum in 1958 to summarize three key factors that influence whether or not a person will participate in preventive programs, originally in the context of tuberculosis screening:

1. Does the person feel motivated to take action? This depends on how susceptible they perceive themselves to be to the disease in question, and by how severe they judge the disease to be.
2. How cost-effective do they judge the recommended action to be? Will it prevent the disease or reduce its severity? Are there psychological, financial, and other costs or barriers involved in the proposed action?
3. There must also be some cue that triggers an actual change in health behaviour. This can be internal (e.g., development of symptoms) or external (e.g., a friend gets sick, or the doctor’s advice).⁶⁶

The Theory of Planned Behavior

Developed in the 1980s, Ajzen’s Theory of Planned Behavior (TPB) extended the HBM. Like the HBM, this assumes that health behaviour can be analysed in terms of rational planning,⁶⁹ as summarized in the top line of Figure 2.6. But the theory also incorporates social and cultural influences via the idea of subjective norms: the person’s perception of social pressures to behave in a certain way (middle row of the figure). Subjective norms incorporate the person’s beliefs about how others view his current and proposed behaviours, and how much he values the opinions of his reference group. The third element of the TPB concerns whether or not the person feels capable of making the proposed change—his perceived behavioural control. This reflects his perceptions of barriers to the action and his confidence in being able to overcome such barriers, a notion that resembles self-efficacy.

These models remind us of the broad range of factors that influence health behaviour, illustrating why merely offering a patient advice is unlikely to be effective. But the models also suggest that the factors that do influence behaviour are logical, so health behaviour need not appear mysterious to the clinician. Most strategies for changing health behaviours, the obvious central interest for the physician, incorporate these factors, as described in Chapter 8.

Other terms applied to the factors included in these behavioural models mention predisposing, enabling and reinforcing factors. Predisposing factors include, for example, the person’s health awareness and attitudes toward health risks, and the social pressures on them to behave in a certain way. But these are insufficient to trigger change, and enabling factors assist in the actual transition to a new behaviour. An example would be an employer willing to sponsor an employee’s enrolment in a drug rehabilitation programme. But note that other enabling factors such as ready availability of drugs can also support continued behaviour. Reinforcing factors maintain the change process. Some are internal, such as improved feelings of wellness and the motivation this brings; others are social such as spousal support or monitoring by the physician, and others are environmental, such as no-smoking zones.

Putting it all Together: Interactions Among Determinants

We have presented each health determinant and risk factor separately, but everyone is exposed to them in combination. Furthermore, determinants and risk factors interact, often reinforcing each other. Overcrowded housing promotes transmission of infection; this leads to time off work and hence reduced income, condemning people to live in overcrowded housing. The evolution of such factors over time is illustrated by Ms. Sulawesi’s situation (see box).

In place of a causal chain, the complex associations among determinants and risk factors is often described as a causal web, conveying the idea of multiple causal pathways connecting outer, societal influences via intermediate layers to individual risk factors.⁷² Figure 2.7 illustrates a typical concentric model of social determinants, this one proposed by Dahlgren and Whitehead.⁷³ Spanning national, community and individual factors, such models are generally described as social-ecological or eco-social models of health determinants in that their focus is on the social environment.⁷⁴

Because eco-social models are intended to apply to any health condition, they typically do not illustrate the specific paths along which determinants lead to a particular health condition. Most determinants are, indeed, non-specific (a recession, poverty, lack of education) although some (such as alcohol or tobacco laws) target particular behaviours or diseases (see Resources box “Models of health determinants”, below).

Models of how determinants and risk factors interact have long been used in infectious disease, in which a case of disease arises from an interaction between the person, or host, the disease agent (virus, bacterium or ingested substance, such as tobacco smoke), and the environment: see Figure 2.8. This “epidemiological triad” applies at the pre-clinical and clinical phases of the CLINICAL COURSE in Figure 2.4. Applied to a non-infectious disease, the immediate causal factor, such as an atherosclerotic plaque in a coronary artery, forms the agent.

This epidemiologic triad model is useful for explaining cases of disease after they arise, but (at least until genetic analyses become much more sophisticated) we cannot accurately predict which person will fall sick when exposed to a disease agent. We deal with this uncertainty probabilistically: risk factors increase the statistical probability that a person will fall sick. The probabilistic language of risk is used because very few causes inevitably produce health consequences: additional factors always modify their effect. While traditional cultures often attributed this uncertainty to fate, astrology, or karma, we refer to random variation. As science has increasingly provided explanations for disease, the component of health that is classified as random or chance variation has steadily declined (see Nerd’s Corner box “The role of chance”). The question of whether science will ever be capable of explaining so much that we will be able to predict a patient’s time and cause of passing is one for you to ponder.

Modifying risk factors

A prime motive for identifying risk factors is to direct preventive efforts. These target modifiable risk factors, especially those whose effect on health is not conditional upon a large number of other causal factors: for example not drinking too much alcohol. Because of their direct effect, such factors are often made the object of legislation. Other risk factors form part of a complex causal web, as with the effect of diet on coronary artery disease. Modifying only one such factor may not affect disease outcome: the web is strong and holds up even when some strands are broken. A review of the impact of modifying even multiple risk factors for cardiovascular disease showed that although improvements in risk factors could be achieved, this had little impact on cardiovascular disease morbidity or mortality.⁷⁸ While a clinician may make dietary recommendations to a patient at risk, the association between diet and adverse outcome is generally not consistent enough for legislation to be enacted. Applying eco-social thinking, advocates of population health argue that attention should be directed upstream, towards the underlying determinants that give rise to groups of risk factors, rather than targeting specific factors and particular diseases.

Moving upstream: the health of populations

The ecological model of health introduced in Chapter 1 is often represented by concentric circles of determinants around the individual, as illustrated in Figure 2.7. Figure 2.9 links the metaphor of concentric circles to both a causal analysis and to points of intervention. The upper quadrants of the diagram illustrate the themes of understanding, and analysis: the “Why?” and “How?” questions. Explanations of why a disease is prevalent typically seek answers in the outer circles in the diagram (shown in the north-west quadrant), whereas “How?” questions concern mechanisms and focus more specifically on the inner circles (NE side). Physicians like Dr. Rao direct their attention towards the inner circles: Peter Sulawesi and his immediate environment. By contrast, public health physicians act on broader determinants (e.g. collaborating with the housing authority to improve housing standards), and thus work on the intermediate circles. Meanwhile, the Health and the Environment ministries will need to consider the broadest determinants operating at the outer circles of the diagram. This combination of actions ideally forms an orchestrated set of approaches to improve the health of individuals and of the population at large.

The arrows in the SW part of Figure 2.9 illustrate the idea that the influence of environmental determinants runs from the outer circles inwards: national policies influence communities; urban policies affect neighbourhoods and thence individuals. But at the same time, the SE part suggests that actions of individuals also influence their environment, so that risk and protective factors from inner levels aggregate up to form outer level influences. This is not a simple summation, however, for many interactions occur, in the form of political and social movements. Individual risk factors derive from, but also create, cultural norms, cumulating to form group-level determinants. This distinction returns to the alternative views of population health – as an aggregate of individuals or as something greater than the sum of its parts.

The contrast between determinants and risk factors drawn earlier in this chapter mirrors the distinction drawn by Geoffrey Rose between the causes of patterns of incidence and causes of individual cases.^{79, 80} Figure 2.10 links these distinctions to the population health versus clinical perspectives in analysing health. Analyses in the upper half of the figure represent the population health perspective; they focus on the causes of patterns of health and speak in terms of broad ecological pressures (or determinants) acting on whole groups of people. This predicts absolute risk, or the numbers of cases of disease: INCIDENCE rates. Analyses in the lower half of the diagram mirror a clinical perspective and speak in terms of individual risk factors and relative risk: which individuals are likely to fall sick and why? This perspective views health as explainable by understanding individual characteristics.

Ultimately, both individual and population perspectives are necessary, the first for the clinician who tackles a patient’s risk factors, and the second for the public health specialist who operates on whole populations.

Self-test Questions

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