Introduction

Public health attempts to protect, promote and restore people’s health. Historically, public health was largely directed towards the prevention of disease and death. Initially the focus was on the causes of infectious disease. As successful models of microbial transmission and prevention developed, the emphasis shifted to non-infectious or chronic diseases such as cancer and cardiovascular disease.

Chronic diseases are not caused primarily by infectious agents. They are complex systemic conditions, often influenced by social and environmental influences as well as underlying genetic variability. This has seen the development of more complex models of health, which focus on the interaction of social, cultural, environmental and behavioural influences on disease.

There has been something of a contest between these two approaches to prevention of illness and disease in public health. On the one hand the traditional approach focused on specific causes and epidemiological studies of disease. On the other, a ‘new public health’ emerged, with its emphasis being the social determinants of health and illness.

Ageing was not the main focus for traditional public health either as a process to be investigated or as that part of the life cycle that occurs in later life. Its emphasis was on identifying the specific factors that were associated with the spread of particular infectious diseases and the development of interventions to reduce their likelihood in the population. Often these occurred in children and younger adults.

As infectious diseases declined, particularly in children and younger adults, and life expectancy consequentially increased, the process of ageing became synonymous with the new epidemic of chronic disease. Initially, the focus was on cancer and cardiovascular disease. More recently it has included chronic obstructive pulmonary disease, renal disease, diabetes, mental illness, dementia and musculoskeletal conditions.

The new public health is primarily charged with preventing and managing these chronic conditions. Ageing is therefore much more of a problem for the new public health to struggle with. In fact, today it is not uncommon for the purpose of public health to be characterised as the prevention and management of the ‘diseases of ageing.’¹

For public health and health care more generally, there is a real tension between the desire to promote positive ageing, prevent illness and disease and provide restorative care in the certain knowledge that at the end of life there is a process of physical decline and death. How this tension is resolved is a critical factor for the design of today’s health and aged care system.

The changing pattern of life expectancy

There has been a very significant increase in life expectancy over the past century. In Australia life expectancy at birth was about 55 years in 1900. In 2006 it is 81 years (Australian Institute of Health and Welfare [AIHW] 2008). Across the countries included in the Organisation for Economic Cooperation and Development (OECD), overall life expectancy at birth has increased from 68.3 years in 1960 to 78.9 years in 2006 (AIHW 2008; OECD 2008).

In the period from 1900 to the 1960s, gains in life expectancy were largely associated with improvements in infant mortality. In Australia, the infant mortality dropped from about 82 per thousand live births in 1904 to about 5 per thousand in 2004 (Australian Bureau of Statistics 2007).

These spectacular increases in life expectancy came about largely as a result of improved living standards, public health measures for waste management, improved water regulation and the reduction of toxins in the environment in the early part of the last century. Subsequently, greatly improved maternal and infant care, vaccine prevention and better treatment of infectious diseases with sulphonamides and antibiotics were important.

Following the dramatic improvements in infant mortality and the declining rate of deaths from infectious diseases like tuberculosis and polio, age standardised death rates reached a plateaux in the 1950s and 60s. Chronic conditions like cancer and particularly cardiovascular disease became the principle causes of mortality.

New approaches to the study of these apparently non-infectious diseases identified a complex series of underlying social and behavioural risk factors. The incidence and prevalence of these chronic diseases was higher for more disadvantaged populations and strongly associated with particular behaviours such as smoking and physical activity.

More recent public health campaigns have focused on social and behavioural influences on cancer and heart disease, and the increase in life expectancy at age 65 in the period after 1970 is largely associated with declining smoking rates, improved diet, better early intervention and the introduction of effective antihypertensive drugs and more effective acute interventions for acute myocardial cerebrovascular infarction. This has seen a significant decline in the age standardised deaths from cardiovascular disease.

The social impact of longer life

There are a number of social consequences associated with increasing average life expectancy. Increasing life expectancy is strongly associated with the improvement of social, environmental and economic conditions. Typically, the birth rate lags behind the declining death rate. As a result, the overall size of a country’s population tends to increase as life expectancy increases, until eventually birth rates fall below replacement.

Combined with the changing post-war fertility pattern across the OECD, increased life expectancy is producing a dramatically increased proportion of the population aged over 65. The ‘baby boomers’, who were born between 1946 and 1964, begin to turn 65 in 2011. Subsequent to their birth, birth rates declined dramatically in developed countries. Currently, across the OECD 14% of the population is aged 65 or over. Projections indicate that there will be a dramatic increase in the proportion of the older population no longer participating in the labour force as a proportion of the overall labour force. In Australia, the proportion of older people no longer in the workforce as a percentage of the overall labour force was about 25% in 2000. This is predicted to grow to about 53% in 2050 (OECD 2008).

Longer life expectancy and the increasing proportion of older people in the population are changing perceptions and expectations about ageing. As the length of healthy life and the proportion of older people increase, a range of new social and economic policy responses are required to address retirement incomes, housing options, social participation and health care.

It is true that the majority of those aged over 65 will continue to be healthy and active for a significant period as their participation in the labour force declines. But it is also true that ageing is inevitably associated with increased disease, disability and finally death, particularly in the period after 80. Ageing therefore becomes a problem for the community, as understandable concerns that greater population ageing will lead to increased demand for health and aged care services emerge. Not surprisingly, public health is then given the tasks of trying to prevent chronic disease and of finding ways of managing these diseases as efficiently as possible when they occur.

The impact of ageing on demand for health and aged care

Estimates of the impact of population ageing on demand for health services are complex and contested. However, in part, projections depend on the extent to which increased life expectancy is associated with more or less disability, and the impact of the demographic ageing bubble caused by the ‘baby boomers’.

Health care costs rise dramatically with age. Costs are about four times higher for those aged over 65 and significantly higher again for those aged over 80. Across all population age groups, aggregate health care costs peak between 80 and 90. After that they fall again because the size of the age cohort decreases dramatically as the mortality rate increases. A significant proportion of lifetime health care costs are borne in the period immediately prior to death. If disease and injury are prevented it is arguable that healthy life years will be gained. On the other hand, if disease and injury are treated to prolong life, then it is possible that years of life will be gained at the expense of quality of life.

There are two main hypotheses that have been developed to predict the impact of increased life expectancy on health care costs. The expansion of morbidity hypothesis predicts we will live longer, but with greater levels of disease and disability and therefore greater costs (Gruenberg 1977). The compression of morbidity hypothesis suggests we will live longer and that our increased life expectancy will be associated with a decreased period of disease and disability (Fries 1980, 1989).

To understand the debate around the compression or expansion of morbidity it is important to understand the relationship between average life expectancy and maximum lifespan. Despite the significant increase in life expectancy over the past century, there has been little change in maximum lifespan, which remains at about 120 years. Effectively, life expectancy has increased by reducing the incidence and prevalence of disease and injury earlier in life. As morbidity and mortality has declined for younger age groups, morbidity and mortality have been compressed into a narrower range for older age groups. How long can this trend continue?

The compression of morbidity hypothesis proposes that maximum lifespan is set by biological limits that are difficult to alter. Progressive prevention of diseases and injury will result in longer disability-free life expectancy until average life expectancy approaches this limit. As it does, morbidity will increasingly be compressed within a narrower age range.

The expansion of morbidity hypothesis suggests that treatment and intervention will reduce mortality but not the morbidity associated with disease. As a result, life expectancy will increase, but we will live for longer periods with more disease and disability. If this were true, there would be a trade-off between increased duration of life and decreased quality. This hypothesis also implies that maximum life span may shift upwards as well.

The implications for health care costs are significant. If morbidity is compressed there is little impact on health care costs associated with increased life expectancy. Effectively, costs are deferred until later in life. On the other hand, if morbidity expands, health care costs will increase as life expectancy increases. If this occurs, it is likely that each year of healthy life would become increasingly costly. As the average quality of additional years declined, it would also be necessary to make judgments about the relative merit of the increasingly marginal trade-off between the quality and the length of life.

Over the past 40 years, during which life expectancy has increased, there has been some expansion of morbidity (Mathers 2007). However, it appears this expansion has been confined to less severe disability. This suggests that the period of more severe morbidity in the period immediately preceding death may not be expanding as average life expectancy increases.

Some commentators (e.g., Richardson & Robertson 1999) conclude that increased life expectancy will have little impact on ageing. Other factors such as improved technology and economic growth are seen as more significant in general.

However, where there is a significant demographic change that increases the proportion of older people in society, this impact needs to be taken into account. Even if current increases in life expectancy do not result in increased costs, health and aged care costs will increase significantly as the proportion (and absolute number) of older people in the population increases, particularly when the number of people aged over 80 increases (Productivity Commission 2005).

Not surprisingly, governments and the community more generally have become concerned about these costs. In response, they have begun to explore new strategies to prevent and manage the emerging problem of chronic disease.