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Mortality and Morbidity: Mortality of Aboriginal and Torres Strait Islander peoples
Age-specific death rates
In 1998-2000, Aboriginal and Torres Strait Islander males and females at all ages had higher age-specific death rates compared with the total population. In the younger age groups (less than 30 years), and among those aged 65 years and over, death rates for Aboriginal and Torres Strait Islander peoples were approximately four times that of the total population. However, between the ages of 30 and 64 years the death rates of Indigenous Australians were around seven times the rates for the total population in those age groups.
The significantly lower life expectancy of Aboriginal and Torres Strait Islander peoples, compared with the total population, reflects their higher death rates at all ages. This is largely the result of relatively high death rates in adulthood, especially between the ages of 45 and 65 years. In the period 1998-2000, deaths of Indigenous people aged 25 years and over accounted for 18 years of the 21 year gap in male life expectancy and 17 years of the 20 year difference in female life expectancy between the Aboriginal and Torres Strait Islander population and the total population.
Much of the difference between Indigenous and total life expectancy had been attributed to the excessive rates of infant death among Indigenous peoples. In 1998-2000, the death rate for Indigenous infants was around four times the rate in the total population. However, in this period, the higher Indigenous infant mortality accounted for only 1 year of the approximately 20 year difference in life expectancy between the Indigenous population and the total population for both sexes. A major decline in Indigenous infant mortality occurred in the 1970s and is largely attributed to improvements in community infrastructure and intensive Indigenous health programs which focused on maternal and child health.2
AGE-GROUP CONTRIBUTION TO THE LIFE EXPECTANCY(a) DIFFERENCE BETWEEN THE INDIGENOUS POPULATION AND THE TOTAL POPULATION - 1998-2000
(a) Life expectancies for Indigenous peoples are experimental and exclude Tasmania and the Australian Capital Territory.
Source: ABS Deaths Collection.
Within the adult age groups, there were marked differences between males and females in the age group contributions to the difference in life expectancy. The high death rates experienced by Indigenous males aged from 25 to 44 years resulted in one-quarter (5 years) of the life expectancy difference between Indigenous males and the total male population. In comparison, female death rates in this age group contributed three years to the life expectancy gap. In the 65 years and over age group, high female Indigenous mortality contributed over one-third (8 years) of the gap between Indigenous life expectancy and that for the total female population. Death rates among Indigenous males in this age group contributed one-quarter (5 years) of the life expectancy gap.
Analysis of the major causes of death provides further insight into the pattern of higher mortality rates among Aboriginal and Torres Strait Islander peoples. The relative importance of each of these causes of death is also analysed in terms of their impact on the lower life expectancy.
Diseases of the circulatory system, or cardiovascular diseases, which include ischaemic heart disease, stroke and rheumatic heart disease, are the leading causes of death for both Aboriginal and Torres Strait Islander peoples and the total population. In the period 1998-2000, 3,034 Indigenous Australians died of cardiovascular disease, accounting for almost 30% of all Indigenous deaths during that period.
In 1998-2000, deaths from cardiovascular disease among Aboriginal and Torres Strait Islander males were 5.2 times higher than would be expected if the Indigenous population experienced the same age-specific death rates as the total male population. This comparative rate is known as the standardised mortality ratio. The standardised mortality ratio for females was 4.7. In the same period, the median age for deaths of Indigenous males from cardiovascular disease was 58 years, compared with 78 years for the total male population. For Indigenous females, the median age of death from this cause was 65 years, compared with 84 years for all females.
Risk factors contributing to the comparatively high incidence of cardiovascular disease among Aboriginal and Torres Strait Islander peoples include their high rates of smoking, obesity and diabetes.3 In addition, it has been argued that low infant birthweight predisposes a person to cardiovascular disease in later life.4 Thus the high rate of heart disease in Indigenous adults may be due in part to the relatively high proportion of Indigenous babies with low birthweight and the survival of greater numbers of these babies, resulting from improved infant survival rates since the 1950s.5
In 1998-2000, there were 84 deaths of Indigenous people caused by rheumatic heart disease. The median age at death of Indigenous Australians from rheumatic heart disease was 45 years, compared with 75 years for the total population. Indigenous Australians experience particularly high death rates from rheumatic heart disease - around 20 times higher than the rate among the total population in 1998-2000. Rheumatic heart disease is often associated with poor infection control arising in many instances from overcrowding, lack of hygiene and scabies infestation.6
SELECTED CAUSES OF DEATH OF INDIGENOUS PEOPLES(a) - 1998-2000
Source: ABS Causes of Death Collection.
Aboriginal and Torres Strait Islander peoples are more likely than the total population to die from external causes such as accidents, poisonings and violence. External causes also include deaths from transport accidents, falls and intentional self-harm or suicide. In the period 1998-2000, there were 1,613 deaths of Indigenous Australians attributed to external causes, accounting for 16% of deaths, compared with 6% of deaths in the total population. Among Indigenous males and females, there were 4.4 and 4.7 times more deaths respectively than would have been expected from age-specific death rates for the total male and female populations. External causes were the second leading cause of death for Indigenous Australians in 1998-2000, and the fourth for the total population. As a proportion of all Indigenous deaths, suicide accounted for 4.3% (2.0% for the total population), transport accidents 4.2% (1.6%), and assault 2.0% (0.2%).
Malignant neoplasms, or cancers, of the digestive organs and lungs (and other smoking-related cancers) are the most common types of cancer that lead to deaths among Aboriginal and Torres Strait Islander peoples. In 1998-2000, cancer caused 1,485 deaths of Indigenous Australians (nearly 15% of all deaths of Indigenous peoples). While cancer death rates are higher among Indigenous peoples than for all Australians, the standardised mortality ratio of 2.6 for males and 2.5 for females is less than for other leading causes of death.
Indigenous peoples have low cancer survival rates compared with their incidence rates, partly because they are more likely to develop cancers with a poor prognosis (such as lung cancer).7 Another possible factor is that cancers among Indigenous Australians may be detected at more advanced stages than in the total population. For example, cervical and breast cancer are among the most common types of cancer for Indigenous females. Cervical cancer is one of the few potentially preventable cancers, but participation in Pap smear screening in Indigenous communities is thought to be relatively low.7
Other major causes of death
In the period 1998-2000, 828 Aboriginal and Torres Strait Islander people died from diseases of the respiratory system. This represented 8% of all deaths among Indigenous Australians. The standardised mortality ratio shows that Indigenous males died from diseases of the respiratory system at 6.9 times the rate of the total population, and females at 6.0 times the rate.
Endocrine, nutritional and metabolic diseases comprised 8% of all deaths of Indigenous Australians. Of the 822 deaths in this group, 87% (715) were due to diabetes mellitus. Indigenous Australians are over 12 times more likely to die from diabetes than the total population, as measured by the standardised mortality ratio. Diabetes and associated complications, such as cardiovascular and renal disease, are in part due to increasing weight in adulthood and poor diet. The prevalence of diabetes among Indigenous Australians living in remote communities in the Northern Territory is estimated to be between 10% and 20%.8
Possible years of life expectancy gained
Each of the higher death rates for particular causes of death among Aboriginal and Torres Strait Islander peoples, compared with the total population, contributes to their lower life expectancy. The degree to which each cause of death contributes to lower life expectancy for Indigenous Australians can be broken down to represent the difference in years of life expectancy due to each cause. These years indicate the potential years of life expectancy that could be gained if the death rates from these causes could be reduced to those of the total population. The technique used to derive potential years of life expectancy gained for individual causes of death produces gains which add to the total difference in life expectancy between the Indigenous population and the total population.9 However, in reality the potential years of life gained for the individual causes of death are not necessarily cumulative because of the complex interaction between diseases and causes of death.
If the death rate from cardiovascular disease for Aboriginal and Torres Strait Islander peoples was the same as for the total population, life expectancy for Indigenous Australians would increase by around 6.5 years for both males and females. For external causes of death, which are potentially preventable deaths, life expectancy would increase by 3.7 years for males and 1.7 years for females. This difference between males and females in the potential years of life expectancy gained is principally due to greater proportions of males dying at younger ages from external causes, such as traffic accidents and suicides, compared with females.
Assuming cancer death rates among Indigenous Australians were the same as for the total population, the additional years of life expectancy gained would be 2.4 years for males and 2.5 years for females. Gains in life expectancy from endocrine, nutritional and metabolic diseases, which includes diabetes, would be 1.6 years for males and 2.5 years for females.
POTENTIAL YEARS OF LIFE EXPECTANCY(a) GAINED BY INDIGENOUS PEOPLES IF SELECTED CAUSES OF DEATH REDUCED TO THAT OF THE TOTAL POPULATION - 1998-2000
Source: ABS Causes of Death Collection.
1 House of Representatives Standing Committee on Family and Community Affairs 2000, Health is Life: Report on the Inquiry into Indigenous Health, Parliament of the Commonwealth of Australia, Canberra.
2 Thomson, N. 1990, 'Trends in Aboriginal infant mortality' in A Matter of Life and Death: Contemporary Aboriginal Mortality, ed Gray, A., Aboriginal Studies Press, Canberra.
3 Walsh, W.F. 2001, 'Cardiovascular health in Indigenous Australians: A call for action', Medical Journal of Australia, vol. 175, no. 7, pp. 351-352.
4 Barker, D.P.J., Osmond, C., Winter, P.D., Margetts, B.M. and Simmonds S.J. 1989, 'Weight in infancy and death from ischaemic heart disease', Lancet, vol. 2, pp. 577-580.
5 Hoy, W.E., Norman, R.J., Hayhurst, B.G. and Pugsley, D.J. 1997, 'Health profile of adults in a Northern Territory Aboriginal community', Australian and New Zealand Journal of Public Health, vol. 21, no. 2, pp. 121-126.
6 Carapetis, J.R. and Currie, B.J. 1999, 'Mortality due to acute rheumatic fever and rheumatic heart disease in the Northern Territory: A preventable cause of death in Aboriginal people', Australian and New Zealand Journal of Public Health, vol. 23, no. 2., pp. 159-163.
7 Coory, M.J., Thompson, A., Ganguly, I. 2000, 'Cancer among people living in rural and remote Indigenous communities in Queensland', Medical Journal of Australia, vol. 173, no. 6, pp. 301-304.
8 London, J.A. and Guthridge, S. 1998, 'Aboriginal perspectives of diabetes in a remote community in the Northern Territory', Australian and New Zealand Journal of Public Health, vol. 22, no. 6, pp. 726-728.
9 Pollard, J.H. 1989, ‘Mortality changes and their economic consequences with particular reference to cause of death’ in Studies in Contemporary Economies, eds Wenig, A. and Zimmerman, K.F. Demographic change and Economic Development. Springer-Verlag. Berlin, Heidelburg, cited in Jain S.K. 1994, Trends in Mortality, cat. no. 3313.0, National Centre for Epidemiology and Population Health and Australian Bureau of Statistics, Canberra.