3 Determinants of health



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3 Determinants of health

This chapter describes determinants of the health of Australians, providing a background for the great potential of prevention and health promotion. The conceptual framework of health for Australia’s health (Figure 1.1 in Chapter 1) shows determinants as biomedical and genetic factors, health behaviours, socioeconomic factors and environmental factors. The determinants influence health and wellbeing, and can be influenced by interventions and by resources and systems.

The chapter’s introduction presents a framework for determinants of health that illustrates how various determinants can relate to and influence other determinants as well as health and wellbeing. The chapter presents information on the main types of determinants of health in Australia and includes data, where available, on levels, patterns and trends.

3.1 What are health determinants?

The health of individuals and populations is influenced and determined by many factors acting in various combinations. The dominant view is that health is ‘multicausal’: healthiness, disease, disability and, ultimately, death are seen as the result of the interaction of human biology, lifestyle and environmental (including social) factors, modified by health interventions and other measures.

Health determinants can be described as those factors that raise or lower the level of health in a population or individual. Determinants help explain and predict trends in health and explain why some groups have better or worse health than others. They are the key to the prevention of disease, illness and injury.

Determinants may have positive or negative effects. Factors such as tobacco smoking or low socioeconomic status increase the risk of ill health and are commonly termed ‘risk factors’. Positive influences such as a high intake of fruit and vegetables are known as ‘protective factors’. Unlike behaviours, some determinants such as age, sex and genetics cannot be altered.

For almost all risk and protective factors the associated effect is not ‘all or nothing’. For risk factors, rather than there being one point at which risk begins, there is an increasing effect as the exposure increases. For example, each increment in a person’s body weight above their ‘optimal’ level is associated with an increase in the risk of ill health. Although the increasing risk often starts at relatively low levels, the usual practice is to monitor a risk factor by reporting the proportion at the riskier end of the spectrum.

Determinants can vary in the extent to which they represent ‘relative risk’ and ‘absolute risk’ of developing disease. Those that represent a high relative risk are associated with relatively high proportions of people exposed to the risk factor developing disease, although the prevalence of the risk factor may be low, and the absolute number of people that develop disease may be low. Those determinants that represent a high absolute risk are usually associated with relatively high proportions of the population exposed to the risk factor, so that if levels of determinants change, even by small amounts, the result can be large changes in the absolute number of people who develop disease, even though the relative risk of developing disease may not be high. If, for example, a food product provided to a small group of people was contaminated with Salmonella, there would be a high relative risk of food poisoning among the group. However, as the product was only provided to the small group, there would be a relatively low absolute risk of poisoning from the food product in the population as a whole.

In addition to influencing the occurrence of new cases of disease or injury, determinants can affect the continuation and prognosis of chronic diseases and their complications. The use of health care interventions can also be regarded as a determinant in that context. They are described in Chapter 7 and are not covered here.

Determinants can also influence how individuals function, in terms of their activities and participation in society. Aspects of the physical environment can either facilitate functioning or act as a barrier to it, as can the availability of assistance from other people or aids and appliances (WHO 2001).



A framework for determinants

Determinants are in complex interplay and range from the ‘upstream’ background influences (such as culture and wealth), with many health and non-health effects that can be difficult to quantify, to immediate or direct influences with highly specific effects on particular aspects of health. They are often described as a web of causes, but they can also be thought of as part of broad causal ‘pathways’ or ‘chains’ that affect health. Figure 3.1 is a simple framework of determinants and their pathways, with the general direction of effects going from left to right.

General background factors and environmental factors can determine the nature of socioeconomic characteristics and both can influence people’s health behaviours, their psychological state and factors relating to safety. These in turn can influence biomedical factors, such as blood pressure and body weight, which may have health effects through various further pathways. At all stages along the path these various factors interact with an individual’s genetic composition. In addition, the factors within each group in Figure 3.1 often interact and are highly related to each other. (Despite the general direction of these influences they can occur in reverse. For example, an individual’s health can also influence their physical activity levels, employment status and wealth.)

General background factors

General background factors affect virtually all people in society to some extent, although to varying degrees. These factors combine to influence the basic levels of security, safety, hygiene, nourishment, technology, information, freedom and morale of societies. It is difficult to put values and quantities on most of these broad factors, let alone measure them and assess their impact precisely. However, it is widely agreed that, at least up to a fair degree of societal development, they are a vital determinant of a population’s health. They set the background level around which variations then occur between groups and individuals.





Figure 3.1: A conceptual framework for determinants of health

Included in these general background factors are wealth and social cohesion. Wealth or accumulated assets can buffer material living standards, for example in periods of low income (AIHW 2005a). The Household Income and Labour Dynamics in Australia survey showed that, in 2002, the least wealthy 50% of households owned less than 10% of total household wealth, while the wealthiest 10% owned 45% of total household wealth.

Social cohesion can be defined as the connections and relations between societal units, such as individuals, groups and associations, or the glue that holds communities together (AIHW 2005a), and links with aspects of socioeconomic characteristics in the framework. Levels of social cohesion are indicated by the fact that the majority of Australians are confident they can rely on their support network in times of crisis, and make contact with family and friends on a weekly basis. A third of Australians engage with the wider community, mostly as volunteers, and three-quarters donate money to charities and non-profit organisations. Markedly smaller percentages are civically engaged, in terms of being regularly involved in the activities of a political, advocacy or community organisation. However, less than half of Australians are socially trusting (that is, of less well-known acquaintances and strangers), domestic violence and child abuse remain very real for some Australian females and children, and rates of imprisonment increased markedly between 1994 and 2004 (AIHW 2005a).

Environmental factors

As described here, environmental factors include the physical environment, such as the climate, the land, plant and animal life, and human-made factors such as chemical pollution, the built environment and waste products. Among many things, these can affect a society’s supply of water, and food and other primary products, and therefore its wealth, and they can influence where and how people live and spend their time. Large-scale environmental disruptions, such as human-induced climate change, can have major health implications in the longer term as well as in the short term. Environmental determinants are detailed further in Section 3.2.



Socioeconomic characteristics

Socioeconomic characteristics are influenced by society’s policies, structures and history, and can be affected by environmental factors as well. Variations in socioeconomic characteristics can in turn lead to marked variations in health. Differences in people’s levels of education and income, for example, can lead to strong differences in the opportunities and choices that affect their health. Socioeconomic characteristics that can influence health are described in Section 3.3.



Knowledge and attitudes

Knowledge, attitudes and beliefs are influenced by general background factors such as culture and resources, by education, and by families and social settings. They affect health through influencing lifestyle behaviours, help-seeking behaviours, and other health decisions. A selection is described in Section 3.4.



Health behaviours

General background factors, varying socioeconomic factors and knowledge and attitudes can influence health behaviours. A particular health behaviour such as an individual’s diet, for example, can result partly from the general availability and range of foods due to the system as a whole. It can also reflect a person’s ‘inherent’ preferences modified by cultural and family influences and by knowledge of food values. Finally, it may further reflect the person’s financial and political freedom to exercise those preferences. Some important behavioural determinants of health are detailed in Section 3.5.



Psychological effects

A person’s psychological state and behaviour clearly affect each other and both can in turn lead to biomedical changes or disease. Diseases such as asthma, for example, are believed to be often influenced by psychological factors (AIHW: Australian Centre for Asthma Monitoring 2003). There is also evidence that depression, social isolation and a lack of quality social support can lead to problems such as heart disease, independent of any intermediary behavioural effects (Bunker et al. 2003).



Safety factors

Safety factors can be regarded as related to behaviour, policies and to the built or human-made environment; and they are influenced by education, knowledge and attitudes, and also by socioeconomic influences on choices. Safety factors influenced by combinations of behaviour, socioeconomic conditions and policies include seat belt-wearing, home smoke detectors, unsafe product recalls, levels of crime, car airbags and road improvements.

Direct experiences or perceptions of safety can greatly affect a person’s physical and mental health and wellbeing. Most but not all people feel safe or very safe at home after dark, an estimated 8.9% of households experienced at least one household crime in the 12 months prior to the 2002 National Crime and Safety Survey, and an estimated 5.3% of people over 15 years were victims of at least one personal crime (ABS 2003a). In the 2002 ABS General Social Survey, 9.0% of persons aged 18 years or over reported being victims of physical or threatened violence (ABS 2003b). The burden of injury was estimated (provisionally, at the time of writing) to be 245,600 disability-adjusted life years (DALYs) in 2003 (Chapter 2).

Biomedical factors

Biomedical risk factors are determinants derived from body measurements, such as overweight, high blood pressure and high blood cholesterol. Because they are ‘within the body’, biomedical risk factors can be regarded as ‘downstream’ in the causal process, and they can be shown to carry comparatively direct and specific risks for health. They are often influenced by behavioural factors which are in turn influenced by socioeconomic factors and other ‘upstream’ determinants. Health behaviours tend to interact with each other and to influence a variety of biomedical factors. Both physical activity and diet, for example, can affect body weight, blood pressure and blood cholesterol. They can do this alone or, with greater effect, together. Behavioural and biomedical risk factors tend to increase each other’s effects when they occur together in an individual. Information on three important biomedical factors is presented in Section 3.6.



Individual makeup

Determinants act upon and are influenced by an individual’s makeup, both physical and psychological. This makeup can greatly modify a person’s response to other new or continuing determinants. It can be seen as the complex product of a person’s genes, intergenerational effects, their ageing, and physical or social influences at various stages over their life course. These influences can become built into a person’s makeup for various periods or for life. Some diseases, such as muscular dystrophy, result entirely from a person’s genetic features, whereas most others reflect the interaction between those features and the many other influences mentioned here.



Determinants of the burden of disease

In most parts of this chapter, information is presented for specific determinants. The population health impact of individual risk factors varies, depending not only on their prevalence in the population, but also on their relative effects in contributing to disease and mortality. Table 3.1 aims to give a perspective on the impact of biomedical and behavioural determinants by providing an estimate (provisional at the time of writing) of their relative importance in 2003 measured in terms of their causal contribution to morbidity and mortality in Australia. From this, overweight was estimated to cause the most premature death and illness, followed by tobacco smoking and high blood pressure.



Table 3.1: Proportion of disease burden attributed to selected determinants of health (per cent)

Determinant

Males

Females

Persons

Overweight

8.8

8.3

8.6

Tobacco smoking

9.5

6.1

7.9

High blood pressure

7.5

7.0

7.3

Physical inactivity

6.5

6.8

6.7

High blood cholesterol

6.5

5.7

6.1

Alcohol harm

5.3

2.2

3.8

Alcohol benefit

–1.6

–2.1

–1.8

Occupational exposures

2.6

1.3

2.0

Illicit drugs

2.6

1.2

1.9

Lack of fruit/vegetables

1.9

1.0

1.4

Intimate partner violence

n.a.

2.1

1.0

Child sexual abuse

0.3

1.3

0.8

Unsafe sex

0.4

0.6

0.5

n.a. Not available.

Note: Attributable disability-adjusted life years (DALYs) as a proportion of total DALYs. One DALY equals one year of healthy life lost through premature death or living with disability due to illness or injury (see Chapter 2). Data are provisional at the time of writing.

Source: AIHW: Begg et al. in press.

3.2 Environmental factors

Environmental factors include many physical, chemical and biological conditions and agents that may affect human health, both positively and negatively. Clean air, water and food, and safe human-made environments benefit the health and wellbeing of individuals and communities. On the other hand, the natural environment and natural disasters can be harmful, as can human-caused changes such as land degradation, freshwater depletion and climate change.

Environmental influences on health can be direct or indirect, obvious or subtle, straightforward or complex, and immediate or delayed. This makes it challenging to estimate the full range and size of the harmful health effects of the environment. These include communicable diseases due to microbial contamination of food or water, vector- borne diseases transmitted by insects such as mosquitoes, respiratory and heart diseases due to air pollution and chemicals in workplaces, other consequences of chemical toxicity, effects of noise and heat, and injuries due to poorly designed traffic systems and home or workplace environments. The increasing interest in global climate change has focused attention on how ecological systems influence disease occurrence.

According to the 2001 State of the Environment report (Australian State of the Environment Committee 2001), urban air quality has generally improved since 1996, streetscapes and parks in most urban areas are better, and there is greater energy efficiency in residences. However, over the same period the quality of water bodies deteriorated and invasive species have continued to pose a serious problem. Furthermore, many of the warmest years on record in Australia have occurred in the last two decades, with 2005 having been the warmest.



Food quality

Contamination of food anywhere on the food chain from ‘paddock to plate’ can lead to foodborne illness. An estimated 4–7 million cases of foodborne infection (gastroenteritis) occur annually in Australia (Hall et al. 2005) and foodborne infectious illnesses other than gastroenteritis can also occur. Various pesticides and other non-natural contaminants can also be found in some foods, but the estimated average dietary exposures to pesticides and other contaminants in Australia remain within acceptable health standards (FSANZ 2002).

Poor hygiene and temperature control in any part of the food production chain can potentially lead to illness. Preventing foodborne illness relies on a complex system of regulation, increasingly based on assessing risks associated with food businesses. The Hazard Analysis and Critical Control Point system relies on a food business identifying potential hazards and the control measures needed (NSW Health 2006). Food safety also depends on kitchen hygiene levels, including in households.

Foodborne infections

Foodborne pathogens that commonly cause gastroenteritis in Australia include the bacteria Salmonella and Campylobacter and viruses such as noroviruses (Sinclair et al. 2005). Sometimes the illness is part of a recognised ‘outbreak’ with a known food responsible for infecting a number of people. In 2004, 118 such outbreaks affected 2,076 people (OzFoodNet Working Group 2005).

Data from the OzFoodNet outbreak register indicate that high-risk foods include raw eggs, poultry, fish, oysters, and commercial foods like kebabs, bakery products and pizzas. Increasingly, fresh produce is being implicated as the cause of outbreaks, particularly salads, fruit juice and sprouts (Dalton et al. 2004).

In Australia, notification rates for potentially foodborne infections have increased over recent decades. This is partly because of more complete reporting and improved laboratory capacity to identify pathogens, but is probably also due to changed behaviours—people are eating more takeaway and pre-prepared meals, which may pose higher risks if not well prepared. Australia has well-regulated hygiene standards in the food production industry, but the increased scale of production, processing and distribution in recent decades has increased the potential for widespread outbreaks of foodborne infection (Kirk et al. 2004).



Water quality

Providing a safe drinking water supply is fundamental to maintaining good public health. This includes issues of both quantity and quality. In modern Australia, with escalating demands for fresh water, there are increasing concerns about the sufficiency of supplies for domestic consumption and hygiene in some regions.

Water quality depends on controlling the concentrations of potentially harmful chemical and microbial contaminants, which may originate from natural or human-made sources. In Australia, 93% of households are connected to mains water supplies, and over 80% use mains water as their primary source of drinking water. Other important sources of drinking water are rainwater tanks (11% of households), particularly in rural areas, and bottled water (7.6%) (ABS 2005a).

Fluoridation of tap water delivers public health benefits by reducing dental caries, and about two-thirds of Australians are currently supplied by fluoridated mains water (Box 3.1).



Box 3.1: Population exposure to fluoridated drinking water

The most effective public health measure for preventing dental decay is the adjustment of fluoride in drinking water to a range of 0.5 parts per million to 1.0 part per million (varying by climate to reflect differences in patterns of water consumption). Over two-thirds of Australians (69.1%) live in areas where the public water supply meets these requirements. High percentages in most states and territories reflect the fact that their capital cities are fluoridated. The exception is Queensland, where Brisbane and most regional centres are not fluoridated.

Exposure to fluoridated drinking water(a)

State/territory

% of population

NSW

89.8

Vic

75.3

Qld

4.7

WA

90.1

SA

90.2

Tas

94.7

ACT

100.0

NT

84.2

(a) Percentage of state/territory population living in areas with fluoride in public water supplies.

Fluoride from natural or engineering sources at concentrations of 0.7 parts per million or more (except SA and NT where concentration is 0.5 parts per million or more).



Source: AIHW Dental Statistics and Research Unit, unpublished data.

Microbiological risks from drinking water are mainly due to contamination by harmful micro-organisms from human or animal faeces. A broad range of viruses, bacteria and protozoa can be transmitted by contaminated water supplies. Disease outbreaks from public water supplies are rare in Australia, but they periodically occur from small private water supplies.

Chemical contaminants in water may arise from natural sources; for example, arsenic, nitrate or fluoride occurs in some groundwater supplies with particular geological characteristics. Other chemical contamination may result from human activities (for example, agricultural herbicides and pesticides in surface-water supplies). While national data are not available, results for New South Wales in 2003 indicate that almost 100% of drinking water samples met guidelines for permissible levels of inorganic chemicals and pesticides (Population Health Division 2004).

In some parts of Australia, drinking water quality may be affected by cyanobacterial (blue-green algae) blooms and their toxins, resulting from increased nutrient levels, warm water temperatures and reduced water flows. While odour and flavour are impaired, health risks remain uncertain.

Managing the quality of drinking water requires multiple barriers to reduce potentially harmful contaminants to acceptable levels before water is supplied to consumers. Barriers may include protection of source waters, prolonged storage to reduce contaminant levels, filtration and disinfection, and maintaining the physical integrity of the distribution system. This multi-barrier approach was strengthened by the adoption of a national risk assessment and risk management framework as the central focus of the Australian Drinking Water Guidelines in 2004 (NHMRC 2004).

Although most Australians have access to good quality drinking water, the 2001 Community Housing and Infrastructure Needs Survey found that 56 of the 169 Indigenous communities (about 17,000 people) that had been tested had drinking water supplies that failed testing at least once in the 12 months before the survey (ABS 2002a).

Water-based recreation promotes healthy physical activity and enhances wellbeing, but may also expose participants to microbial (such as blue-green algae) or chemical contaminants. The quality of natural recreational water bodies may be affected by discharges of sewage, stormwater and agricultural runoff, while risks to swimming pool water quality arise from microbial contaminants originating from bathers themselves. Public swimming pools have been the source of a number of outbreaks of cryptosporidiosis in recent years in Australia.

Animal vectors and reservoirs of disease

The occurrence of vectorborne and zoonotic diseases (diseases that can be transmitted from animals to humans) diseases fluctuates considerably with patterns of human mobility, trade, weather, and the ecology of vector species such as mosquitoes and of reservoir species such as birds. Changes in the environment, weather and climate, but also mosquito control activities, influence the prevalence and geographic range of some mosquito-borne diseases within Australia. These include dengue (188 cases notified in Australia in 2004–05), Ross River virus disease (1,858), Barmah Forest virus disease (1,256) and, sometimes with more serious consequences, diseases caused by Murray Valley encephalitis (2 cases in 2004–05), Kunjin virus (4 cases) and Japanese encephalitis virus (no cases in 2004–05) (CDNA 2005).

Other infectious diseases can be spread by ticks and flies. Flies are also responsible for the spread of the eye disease trachoma in remote Indigenous communities. Mammals and birds act as natural reservoirs for a variety of pathogens that cause infectious diseases in humans. Since 2003, birds have acted as a reservoir for avian influenza (‘bird flu’), which had caused 177 laboratory-confirmed cases in humans (including 98 deaths) worldwide by March 2006, mainly in Asia (WHO 2006). No cases had been recorded for Australia.

Providing information relevant to the risk of acquiring mosquito-borne disease, sentinel chicken surveillance is undertaken in New South Wales, Victoria, Queensland, Western Australia and the Northern Territory, to detect and provide early warning of activity of Murray Valley encephalitis virus and Kunjin virus. In addition, sentinel pig surveillance is conducted in Queensland (Cape York and the Torres Strait) to monitor Japanese encephalitis virus activity. Media warnings are issued when virus activity is detected, advising local residents of the need to take added precautions to avoid mosquito bites.

The sentinel flocks of chickens are tested for evidence of new infections throughout the year in some sites, and during summer months in others. In the 2004–05 season (in which there was no surveillance in Queensland), Murray Valley encephalitis virus activity was detected in the Top End of the Northern Territory and in the Kimberley in Western Australia; and Kunjin virus activity was detected in the Northern Territory. The sentinel pig surveillance detected Japanese encephalitis virus in the Torres Strait (CDNA 2005).

Air pollution

Air quality in Australia is relatively good by international standards (Manins et al. 2001) but requires regulation and continual monitoring. The air can be contaminated by pollutants, micro-organisms and odours, all of which can be harmful. The health effects of air pollutants range from mild respiratory symptoms through to asthma, cardiovascular conditions and premature mortality. Whereas older people are most at risk, the very young are also at risk (BTRE 2005). Lead exposure damages nerve function and can be a particular concern in the mental development of children.

Recent studies based in Brisbane, Sydney and Melbourne have found an association between air pollution levels and mortality and/or hospital admissions (EPA Victoria 2000, 2001; Morgan et al. 1998a, 1998b; Petroeschevsky et al. 2001; Simpson et al. 2005a, 2005b). A recent report estimated that motor vehicle pollution accounted for between 900 and 2,500 cases of cardiovascular disease, respiratory disease and bronchitis in 2000, and between 900 and 2,000 early deaths (BTRE 2005).

Ambient (that is, outdoor) air pollution in Australia is mainly caused by emissions from motor vehicles, heavy industry and mining activities. Air may also contain emissions from the combustion of fossil fuels for electricity generation, smoke from home heating and bushfires, and wind-blown dust. Indoor air may contain pollutants such as nitrogen dioxide from unflued gas heaters, volatile organic compounds from surface coatings and adhesives, moulds from moist surfaces, and tobacco smoke.

Environmental regulation has markedly reduced the ambient levels of sulfur dioxide, nitrogen dioxide, lead and carbon monoxide (BTRE 2005), and the concentration of lead in urban air has decreased substantially since unleaded fuels were introduced in the mid-1980s (Australian State of the Environment Committee 2001). However, levels of nitrogen oxides and of particulate matter with diameters of up to 10 microns (PM10) are of ongoing policy concern, as are those with diameters less than 2.5 microns (PM2.5), known to cause respiratory and cardiovascular illness.

Australia’s National Environment Protection Council has established an Ambient Air Quality National Environment Protection Measure (NEPM), which includes air quality standards for nitrogen dioxide, PM10, carbon monoxide, sulfur dioxide, photochemical oxidants (as ozone) and lead. Levels of these pollutants are regularly measured in a number of sites around Australia and reported in terms of the number of days per year when the average concentration exceeds the NEPM. Ozone is measured as an indicator of the amount of photochemical smog; it is not a directly emitted pollutant but is formed in a reaction between volatile organic compounds and nitrogen oxides under sunlight.

The number of days per year in which the concentration of PM10 exceeded the NEPM standard level of 50µg/m3 was generally higher in Sydney and Melbourne than in the other major capital cities during the period 2000–04 (Table 3.2). Perth was the only city which did not exceed the maximum allowable days of PM10. Ozone concentrations exceeding 0.10 ppm were more frequent in Sydney than in the other major capital cities. No obvious trend of increase or decrease in ozone levels occurred for any of the capital cities during this period.

The concentration of lead in urban air has decreased substantially in Australia since unleaded fuels were introduced in the mid-1980s (Australian State of the Environment Committee 2001). However, the historical and ongoing accumulation of lead in smelting centres such as Port Pirie in South Australia and Broken Hill in New South Wales continues to pose health risks, particularly for children. These centres have been the focus of efforts to reduce childhood lead exposure and, over the past 20 years, there have been substantial exposure reductions, with recent exposures close to the exposure ranges observed in non-industrial settings before the removal of lead from petrol.



Table 3.2: Days per year when concentrations of PM10 and ozone exceeded the ambient air quality NEPM standard levels, major capital cities, 2000–04




2000

2001

2002

2003

2004

Number of days when concentration of PM10 exceeded 50µg/m3 (over 24 hours)(a)

Sydney

2

5

17

10

2

Melbourne

0

2

6

13

11

Brisbane

0

1

7

2

2

Perth

0

1

2

1

1

Adelaide

n.a.

n.a.

1

6

4

Number of days when concentration of ozone exceeded 0.10 ppm (over 1 hour)(b)

Sydney

4

9

2

4

7

Melbourne

1

0

0

2

1

Brisbane

0

0

2

0

0

Perth

0

0

0

0

1

Adelaide

n.a.

n.a.

0

0

0
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