Summary of the cardiovascular health status of Indigenous peoples

Introduction

Cardiovascular disease (CVD) is a major health problem in the Australian Indigenous population. Most cardiovascular conditions are more common among Indigenous people than among non-Indigenous people. CVD is a significant cause of hospitalisation for Indigenous people, and the leading cause of death for Indigenous males and females at much higher rates than for their non-Indigenous counterparts.

The leading cardiovascular conditions contributing to the higher mortality are coronary heart disease (also known as ischaemic heart disease), cerebrovascular disease (including stroke) and hypertensive disease. Rheumatic heart disease, now an uncommon cause of death for non-Indigenous people, still causes a considerable number of deaths among the Indigenous population, primarily because of the persistence of acute rheumatic fever, especially in children.

The prevalence of cardiovascular conditions among Indigenous Australians is attributed to a range of risk factors. Reducing the risk factors that predispose the Indigenous population to CVD is expected to reduce the prevalence and mortality from all CVDs. In order to accomplish this, attention must be placed on primary and secondary prevention, as well as rehabilitation of patients who have experienced a cardiovascular episode.

This summary focuses on the burden of cardiovascular disease for Indigenous people in terms of the overall levels (prevalence and incidence), hospitalisation and mortality, and on the factors contributing to this burden.

The summary begins with information about the overall burden of cardiovascular disease. It then describes the burden for a number of specific conditions - coronary/ischaemic heart disease, cerebrovascular disease (including stroke), hypertension, acute rheumatic fever and rheumatic heart disease, and congenital heart disease.

The factors contributing to the burden of cardiovascular disease among Indigenous people are considered within a 'social determinants of health' framework, placing the more proximal behavioural and biomedical 'risk factors' within an appropriate context.

Overall levels of cardiovascular disease

Prevalence

The most recent source of information about the extent of CVD among Indigenous people is the National Aboriginal and Torres Strait Islander Health Survey (NATSIHS) undertaken by the Australian Bureau of Statistics in 2004-2005 [1]. Almost one-in-eight Indigenous people reported in the survey having a long-term heart or related condition, with the proportion being slightly higher for those living in remote areas (14%) than in non-remote areas (11%).

A detailed analysis of the survey results undertaken by the AIHW revealed that long-term heart and related conditions were 1.2 times more common for Indigenous males and 1.4 times more common for Indigenous females than for their non-Indigenous counterparts (Table 1) [2]. All specific conditions were more common for Indigenous males and females than for non-Indigenous males and females, with hypertension being the most common cardiovascular condition among Indigenous people.

Table 1: Numbers, percentages and ratios of cardiovascular conditions, Indigenous people, by sex and condition, Australia, 2004-2005

Condition	Males			Females
	Number	Per cent	Ratio	Number	Per cent	Ratio
Source: [2]
Notes: Per cent is the percentage of all Indigenous males and females Ratios are standardised prevalence ratios - the reported Indigenous numbers divided by the numbers expected from the age-sex-cause specific prevalences for the non-Indigenous populations In view of the relatively small numbers involved, the estimates for cerebrovascular disease, heart failure and rheumatic heart disease should be interpreted with caution
Coronary/ischaemic heart disease	2800	1.2	1.7	3000	1.2	2.7
Cerebrovascular disease (including stroke)	700	0.3	1.5	700	0.3	1.9
Heart failure	1400	0.6	1.9	3100	1.3	1.6
Hypertension	15000	6.4	1.5	18700	7.7	1.7
Rheumatic heart disease	900	0.4	n/a	2600	1.1	n/a
Other conditions	1200	0.5	n/a	5800	2.4	n/a
All CVD	22000	9.5	1.2	33900	14.0	1.4

Mortality

CVD was the leading cause of death for Indigenous people living in Queensland, Western Australia, South Australia, and the Northern Territory combined in the period 2001-2005, being responsible for 27% of deaths [3]. The number of Indigenous deaths from CVD was more than three times the number expected from the rates for the non-Indigenous population i.

The leading specific cause of death for both Indigenous males and females in these jurisdictions in 2002-2005 was coronary (or ischaemic) heart disease, for which there were around three times more deaths than expected (Table 2) [2]. The ratio of the number of deaths observed to the number expected is known as the standardised mortality ratio (SMR). For cerebrovascular disease (including stroke), the SMR was 2.1 for males and 1.8 for females. Rheumatic heart disease was responsible for relatively few deaths, but the SMR was 15.1 for males and 23.0 for females.

Table 2: Numbers of Indigenous deaths from CVD and standardised mortality ratios (SMRs), by sex, Queensland, WA, SA, and the NT, 2002-2005

Cause of death	Males		Females
	Number of deaths	SMR	Number of deaths	SMR
Source: [2]
Notes: ICD codes for specific forms of CVD are shown in parentheses 'Cerebrovascular diseases’ includes stroke The numbers shown here have been derived from annual averages, so may differ slightly from actual numbers The SMR is the ratio of the numbers of deaths observed to the numbers expected from the age-sex-cause specific rates for the non-Indigenous populations
Coronary/ischaemic heart disease (I20-I25)	564	3.3	332	2.8
Cerebrovascular diseases (I60-I69)	112	2.1	132	1.8
Heart failure (I50)	16	2.0	28	2.4
Rheumatic fever and rheumatic heart disease (I00-I09)	20	15.1	52	23.0
Other CVD	152	3.0	140	3.1
All CVD (I00-I99)	864	3.1	684	2.7

Age-specific death rates

The striking difference between Indigenous and non-Indigenous people in CVD mortality is the much greater impact among young and middle-aged Indigenous adults. For all CVD, the death rates for Indigenous people living in Queensland, WA, SA and the NT in 2002-2005 were 7 to12 times higher than those for non-Indigenous people in the 35-44 and 45-54 age groups (see Figures 1 and 2) [2]. The death rates for Indigenous people in these age groups were similar to those for non-Indigenous people around 20 years older.

Figure 1 Death rates for cardiovascular disease, by Indigenous status and age group, males, Queensland, WA, SA and the NT, 2002-2005

Source: [2]
Note: Rates are per 100 000 population

Figure 2 Death rates for cardiovascular disease, by Indigenous status and age group, females, Queensland, WA, SA and the NT, 2002-2005

Source: [2]
Note: Rates are per 100 000 population

Hospitalisation

The much higher prevalence of CVD for Indigenous people is partly reflected in hospitalisation rates, details of which are available for NSW, Victoria, Queensland, WA, SA and the NT (public hospitals only) [3][4]. There were more than 8 550 episodes of hospitalisation for CVD for Indigenous people living in these jurisdictions in 2007-08, at a rate 1.8 times that of non-Indigenous people [4] ii.

The more detailed data available for the two-year period July 2004 to June 2006 are similar overall, with the number of episodes of hospitalisation for Indigenous males being 1.9 times the number expected from the age-cause-specific rates for non-Indigenous males, and the number for Indigenous females being 2.3 times the number expected from the age-cause-specific rates for non-Indigenous females [3].

Table 3: Numbers, rates and ratios of hospitalisation of Indigenous people for cardiovascular conditions, by sex and disease category, NSW, Victoria, Queensland, WA, SA and the NT, July 2004-June 2006

Cardiovascular disease category	Males			Females
	Number	Rate	Ratio	Number	Rate	Ratio
Source: AIHW 2009 (Table 1.05.5)
Notes: Categories are based on the ICD-10-AM. Figures shown in italics (acute myocardial infarction and stroke) are sub-categories of the categories immediately above Rates are directly age-standardised rates using the 2001 Australian standard population Ratios are the numbers of hospitalisations of Indigenous males and females divided by the number expected from the age-sex-cause specific rates for non-Indigenous people. All ratios are significant at the p<0.05 level
Ischaemic heart disease	3778	17.7	1.7	2820	12.8	2.7
Acute myocardial infarction	1468	6.8	2.1	978	4.3	3.4
Pulmonary and other forms of heart disease	2352	12.2	1.7	2207	10.5	2.1
Cerebrovascular disease	633	3.7	1.6	651	3.1	2.1
Stroke	572	3.4	1.9	575	2.7	2.2
Acute rheumatic fever and rheumatic heart disease	241	0.4	4.8	445	0.8	8.6
Hypertensive diseases	229	0.9	3.4	359	1.5	4.0
Other circulatory conditions	808	3.4	0.6	791	3.0	0.6
All CVD	8041	38.3	1.5	7273	32.8	2.0

Hospitalisation rates for CVD were higher for Indigenous people than for non-Indigenous people across all age groups (Figure 3).

Figure 3 Hospitalisation rates for cardiovascular disease, by Indigenous status and age group, persons, NSW, Victoria, Queensland, WA, SA and the NT, July 2004-June 2006

Source: AIHW 2008 (Figure 1.05.2)
Note: Rates are per 1 000 population

Coronary heart disease

Prevalence and hospitalisation

Coronary heart disease was reported as a long-term condition by 2 800 Indigenous males and by 3 000 Indigenous females in the 2004-2005 NATSIHS (Table 1) [1]. These levels were 1.7 and 2.7 times higher respectively than those for non-Indigenous males and females.

There were almost 6 000 admissions to hospital of Indigenous people for coronary heart disease in NSW, Victoria, Queensland, WA, SA and the NT in the two-year period July 2004 to June 2006 (Table 3) [4]. Of these admissions, almost 2 550 were for ischaemic heart disease. Admission rates for Indigenous males were 1.7 times higher for ischaemic heart disease and 2.7 times higher for acute myocardial infarction than the corresponding rates for non-Indigenous males.

Mortality

As noted above, the SMRs for coronary heart disease for Indigenous people living in Queensland, WA, SA and the NT in 2002-2005 were 3.3 for males and 2.8 for females (Table 2). An analysis of selected causes of death from cardiovascular disease restricted to people aged 74 years or less living in those jurisdictions in 2002-2006 found that the rate for Indigenous people for ischaemic heart disease was 4.6 times the rate for non-Indigenous people (Table 4) [4].

Table 4: Numbers and rates of death from selected cardiovascular diseases, by Indigenous status, and Indigenous:non-Indigenous rate ratios, people aged 0-74 years, Queensland, WA, SA and the NT, 2002-2006

Cause of death	Indigenous		Non-Indigenous	Rate ratio
	Number	Rate	Rate
Source: AIHW 2009 (Table 1.25.5)
Notes: Categories are based on the ICD-10-AM. ICD codes are in parentheses Rates are directly age-standardised rates using the 2001 Australian standard population Rate ratio is the Indigenous rate divided by the non-Indigenous rate. All ratios are significant at the p<0.05 level
Ischaemic heart disease (I20-I25)	956	149.7	32.7	4.6
Cerebrovascular diseases (I60-I69)	215	36.5	9.8	3.7
Rheumatic and other valvular heart disease (100-109)	93	10.7	0.5	22.7

Full details of deaths from ischaemic heart disease are not available for all age groups, but the rates were very much higher for Indigenous people aged 35-54 years living in Queensland, WA, SA and the NT in 2002-2005 than for their non-Indigenous counterparts (Table 5) [3].

Table 5: Rates of death from selected cardiovascular diseases, by Indigenous status, and Indigenous:non-Indigenous rate ratios, people aged 35-54 years, Queensland, WA, SA and the NT, 2001-2005

Cardiovascular disease category	Indigenous		Non-Indigenous		Rate ratios
	Males	Females	Males	Females	Males	Females
Source: ABS, AIHW 2008
Notes: Categories are based on the ICD-10-AM. ICD codes are in parentheses Rates are per 100,000 population Ratios are the Indigenous rates divided by the non-Indigenous rates
Ischaemic heart disease (I20-I25)	227.7	87.1	32.3	6.1	7.0	14.2
Other selected forms of heart disease (I30-I52)	45.7	21.8	5.6	2.0	8.1	10.8
Cerebrovascular disease (I60-I69)	28.3	24.4	5.5	4.7	5.1	5.2

Cerebrovascular disease (including stroke)

Prevalence and hospitalisation

Cerebrovascular disease was reported as a long-term condition by 700 Indigenous males and by 700 Indigenous females in the 2004-2005 NATSIHS (Table 1) [1]. These levels were 1.5 and 2.9 times higher than those for non-Indigenous males and females.

There were almost 1 300 admissions to hospital of Indigenous people in NSW, Victoria, Queensland, WA, SA and the NT in the two-year period July 2004 to June 2006 (Table 3) [4]. Of these admissions, almost 1 150 were for cerebrovascular disease. Admission rates for Indigenous males were 1.6 times higher for cerebrovascular disease and 1.9 times higher for stroke than the corresponding rates for non-Indigenous males. The rates for Indigenous females were 2.1 and 2.2 times higher than those for non-Indigenous females.

Mortality

The SMRs for cerebrovascular disease (including stroke) were 2.1 for males and 1.8 for females in Queensland, WA, SA, and the NT in 2002-2005 (Table 2).

Full details of deaths from cerebrovascular disease are not available for all age groups, but the rates were very much higher for Indigenous people aged 35-54 years living in Queensland, WA, SA and the NT in 2002-2005 than for their non-Indigenous counterparts (Table 5) [3].

Hypertensive disease

The detailed analysis undertaken by the AIHW of results from 2005-2005 NATSIHS reveal that 6.4% of Indigenous males and 7.7% of Indigenous females reported having hypertension as a long-term condition (Table 1) [2]. Hypertension was more commonly reported by Indigenous people living in remote areas than those living in non-remote areas (10% overall compared with 6%) [1]. After adjusting for differences in the structures of the Indigenous and non-Indigenous populations, the prevalence for Indigenous males was 1.5 times that of non-Indigenous males, and prevalence for Indigenous females 1.7 times that of non-Indigenous females.

The proportions of Indigenous people reporting hypertension as a long-term condition were higher than those of non-Indigenous people for all age groups, with levels among Indigenous people being similar to the levels for non-Indigenous people aged about 10 years older (Figure 4) [2].

Figure 4 Reported proportions of hypertension, by Indigenous status and age group, Australia 2004-2005

Source: [2]

The overall proportion of Indigenous people reporting hypertension as a long-term condition in the 2004-2005 NATSIHS was similar to that reported in the 2001 National Health Survey (NHS), but the proportion of Indigenous people living in remote areas reporting the condition increased from 8% to 10% [1].

The levels of hypertension reported by Indigenous people in the 2001 NHS were similar to those reported 6 years earlier in the 1995 NHS [5] and those documented in a 1988-89 survey of 249 males and 241 females aged 15 or older living in the Kimberley region of Western Australia [6].

On the other hand, the levels reported in the 2004-2005 NATSIHS are considerably lower than the overall prevalence of 32% documented for 592 Torres Strait Islander people surveyed between 1993 and 1997 [7]. Around one-half of the survey participants aged 35 or older were found to be hypertensive (defined as having a systolic blood pressure greater than or equal to 140 mm Hg and/or having a diastolic blood pressure greater than or equal to 90 mm Hg and/or being on anti-hypertensive medication). Only 5% of women aged 15-34 had hypertension, but 18% of men in that age group were hypertensive.

Very similar levels were found among almost 2 900 Indigenous residents of north Queensland (including the Torres Strait Islands) who participated between March 1998 and December 2000 in well person's health checks: 49% of men and women aged 35 or older were found to be hypertensive [8]. The prevalence of hypertension among people aged 15-34 was 17% for males and 5% for females.

Hospitalisation rates for hypertension for Indigenous people living in NSW, Victoria, Queensland, WA, SA and the NT in the two-year period July 2004 to June 2006 were considerably higher than those for non-Indigenous people - 3.4 times higher for males and 4.0 times higher for females overall (Table 3), and between 5 and 7 times higher for males and between 8 and 11 times higher for females in the age groups 25-34, 35-44 and 45-54 years. [4].

Acute rheumatic fever and rheumatic heart disease

Reflecting the continuing importance of acute rheumatic fever (ARF) and rheumatic heart disease (RHD), particularly in the north of Australia, registers were established in 1997 to collect data on new and existing cases.

The registers, which cover the Top End of the NT and central Australia, maintain records of people with known past ARF and/or RHD, and collect information about new cases. This information is essential for an effective secondary prevention program involving antibiotic prophylaxis.

The information presented in this section has been compiled by the AIHW from data extracted from the registers, but does not include data on residents from WA or SA.

Notifications of acute rheumatic fever

There were 251 notifications of new and recurrent cases of ARF in the Top End of the NT and the NT part of central Australia in the four year period 2003-2006 (Table 6) [4]. All except four of these notifications were of Indigenous people. As is generally the case with ARF, more of the Indigenous notifications involved females (145 notifications, 59%) than males (102 notifications, 41%). More than one-half (54%) of the Indigenous notifications were for people aged 5-14 years, with a rate of 2.5 cases per 1,000 population.

Table 6: Numbers and rates of new and recurrent cases of acute rheumatic fever, by Indigenous status and age group, Top End of the Northern Territory and central Australia, 2003-2006

Indigenous status/age group	Number	Rate
Source: AIHW 2009 (Table 1.06.1)
Notes: Data extracted by AIHW from the Top End and central Australian rheumatic heart disease registers Rates per 1 000 are based on estimated resident population figures for 2001 Ratios are the numbers of hospitalisations of Indigenous males and females divided by the number expected from the age-sex-cause specific rates for non-Indigenous people. All ratios are significant at the p<0.05 level
Indigneous
0-4 yrs	5	0.2
5-14 yrs	133	2.5
15-24 yrs	64	1.4
25-34 yrs	22	0.6
35-44 yrs	13	0.5
>=45 yrs	10	0.3
All ages	247	1.1
Non-Indigenous
All ages	4	n/a

Almost three-fifths (58%) of cases notified in the period 1995 to 2006 involved Indigenous residents of the Top End of the NT, but the rates were higher for people living in the NT part of central Australia (Table 7) [4]. There has been no real change between 1995-1997 and 2004-2006 in notification rates.

Table 7: Numbers and rates of new and recurrent cases of acute rheumatic fever among Indigenous people, by region and time period, Top End of the Northern Territory and central Australia, 1995-2006

Time period	Top End, NT		Central Australia
	Number	Rate	Number	Rate
Source: AIHW 2009 (Table 1.06.1)
Notes: Data extracted by AIHW from the Top End and central Australian rheumatic heart disease registers. The data for central Australia are restricted to residents of the NT Crude rates per 1 000 for 1995-1997 and 1998-2000 are based on estimated resident population figures for 1996 and those for 2001-2003 and 2004-2006 on estimated resident population figures for 2001
1995-1997	88	0.8	67	1.3
1998-2000	96	0.9	90	1.7
2001-2003	149	1.3	91	1.7
2004-2006	97	0.8	67	1.2

At 31 December 2006, there were almost 1 300 Indigenous people living in the Top End of the NT and the NT part of central Australia registered as having RHD (table 8) [4]. Almost two-thirds (65%) of these people were females. The overall prevalences of RHD were 1.6% for Indigenous males and 3.0% for Indigenous females, 26 times and 27 times higher, respectively, than the prevalences for non-Indigenous males and females.

Table 8: Rheumatic heart disease registrations, Indigenous people, and Indigenous:non-Indigenous prevalence ratios, Top End of the Northern Territory and central Australia, 31 December 2006

Age group	Males			Females
	Number	Prevelance (%)	Ratio	Number	Prevelance (%)	Ratio
Source: AIHW 2009 (Table 1.06.1)
Notes: Data extracted by AIHW from the Top End and central Australian rheumatic heart disease registers Ratios are the Indigenous prevalence divided by the non-Indigenous prevalence. All ratios are significant at the p<0.05 level
0-14 yrs	132	1.3	28.3	194	2.0	148.7
15-24 yrs	119	2.1	42.7	238	4.2	77.4
25-34 yrs	94	1.9	88.3	184	3.7	37.2
35-44 yrs	44	1.3	29.3	92	2.5	27.5
45-54 yrs	33	1.6	37.1	80	3.6	27.1
55-64 yrs	18	1.7	13.6	38	3.2	8.6
64+ yrs	8	1.2	4.8	14	1.5	3.2
All ages	448	1.6	28.1	840	3.0	27.1

As summarised earlier, these high levels of ARF and RHD are reflected in both hospitalisation and mortality data. Between July 2004 and June 2006, ARF and RHD were responsible for 241 admissions to hospital of Indigenous males and 445 of Indigenous females living in NSW, Victoria, Queensland, WA, SA and the NT at rates 4.8 and 8.6 times respectively than their non-Indigenous counterparts (Table 3). RHD was responsible for the deaths of 20 Indigenous males and 52 Indigenous females living in Queensland, WA, SA, and the NT in 2002-2005, with SMRs of 15.1 and 23.0 respectively (Table 2).

Congenital heart disease

There are few data about the overall extent of congenital heart disease among Indigenous children, with the most comprehensive report being based on notifications received by the Western Australian Birth Defects Registry regarding children born in Western Australia in the 10 year period 1980-1989 [9]. Congenital heart disease was found to be 30% more common among Indigenous than non-Indigenous children, affecting almost 10 out of 1 000 Indigenous children. The overall level for Western Australia was similar to the levels documented for other parts of the world. Congenital heart defects occurring with other defects were significantly more frequent in Indigenous than non-Indigenous children, but the excess of isolated heart defects was of borderline significance. Ventricular septal defect was responsible for more than two-fifths (43%) of cases of isolated congenital heart disease.

More recent data are restricted to the major types of congenital heart disease included in the general reports of congenital anomalies in Australia. For cases reported in Australia in 2002-2003, transposition of the great vessels, tetralogy of Fallot, and coarctation of the aorta were more common among Indigenous people than non-Indigenous people and hypoplastic left heart syndrome less common (Table 9) [10]. None of the differences in prevalence between Indigenous and non-Indigenous cases is statistically significant.

Table 9: Numbers and prevalences for selected types of congenital heart disease, by Indigenous status, and Indigenous:non-Indigenous prevalence ratio, Australia, 2002-2003

Type of congenital heart disease	Indigenous		Non-Indigenous		Ratio
	Number	Prevelance	Number	Prevelance
Source: Abeywardana, Sullivan 2008
Notes: The source document was restricted to these four types of congenital heart disease and doesn’t include cases for the Northern Territory Prevalence is number of cases per 10 000 women who gave birth Ratio is the Indigenous prevalence divided by the non-Indigenous prevalence None of the differences in prevalence between Indigenous and non-Indigenous cases is statistically significant
Transposition of the great vessels	11	7.4	194	4.1	1.8
Tetralogy of Fallot	9	6.1	145	3.1	2.0
Hypoplastic left heart syndrome	2	1.3	79	1.7	0.8
Coarctation of aorta	7	4.7	169	3.6	1.3

Based on a detailed analysis of cases admitted to the Alice Springs Hospital, the overall incidence of congenital heart disease was found to be similar for Indigenous and non-Indigenous babies born in central Australia between 1 January 1993 and 30 June 2000 (Table 10) [11]. Cases, which were confirmed by electrocardiography, excluded patent ductus arteriosus (PDA) in infants born before 37 weeks gestation, asymptomatic PDA in the first 3 months of life, and a number of other minor defects with no clinical significance.

Table 10: Numbers and incidence of congenital heart disease, by Indigenous status and disease type, and Indigenous:non-Indigenous incidence ratio, central Australia, 1993-2000

Disease type	Indigenous		Non-Indigenous		Ratio
	Number	Incidence	Number	Incidence
Source: Bolisetty, et al., 2004
Notes: Based on cases confirmed by echocardiography in the Alice Springs Hospital among babies born between 1 January 1993 and 30 June 2000 Incidence is number of cases per 1 000 live births Ratio is the Indigenous incidence divided by the non-Indigenous incidence None of the differences in incidence between Indigenous and non-Indigenous cases is statistically significant
Ventricular septal defect	30	10.0	32	10.1	1.0
Atrial septal defect	5	1.7	7	2.2	0.8
Patent ductus arteriosus	5	1.7	3	0.9	1.8
Double outlet right ventricle	4	1.3	1	0.3	4.2
Other defects	13	4.3	8	2.5	1.7
All defects	57	19.1	51	16.1	1.2

Factors contributing to CVD among Indigenous people

As is the case with most aspects of Indigenous health, the factors contributing to cardiovascular disease among Indigenous people are complex. They reflect a combination of broad historical, socio-cultural and economic factors as well as the more commonly described 'risk factors'.

The conventional risk factors for cardiovascular disease can be divided into two main categories: behavioural and biomedical. Behavioural risk factors are based on an individual's behavior, such as tobacco smoking, but can be influenced by other underlying social, economic, psychological and cultural factors. Biomedical risk factors, such as high blood cholesterol, can be influenced by modifications to behaviour, lifestyle or use of medical interventions.

Behavioural factors include tobacco smoking, physical inactivity, poor nutrition and risky alcohol consumption [2][12]. Biomedical factors include high blood pressure (hypertension), high blood cholesterol, overweight and obesity, diabetes and chronic kidney disease iii.

'Upstream' factors that have also been recognised as important contributors to the development of cardiovascular disease among Indigenous people include:

• cultural and historical factors, such as loss of land, and disruptions to culture, language and identity [2][13];
• environmental and socioeconomic factors, such as poor housing, low education and income [2];
• psychosocial stressors, such as death of a family member or close friend, serious injury or disability [2]; and
• limited access to health care, both preventive and clinical [14][15].

Of course, many of these upstream factors contribute to the behavioural risk factors. Low education and income, for example, contribute to behavioural factors like cigarette smoking, physical inactivity and nutritional aspects (resulting in some cases in overweight and obesity). It is not known with any certainty, however, the extent to which various upstream factors contribute to biomedical risk factors (such as high blood cholesterol and high blood pressure). Understanding the actual contributions of upstream factors is important in anticipating just how modifiable the behavioural and biomedical risk factors are.

It is also important to recognise that many Indigenous people with CVD also have other health problems and multiple behavioural and biomedical risk factors [16][17][18]. Having more than one risk factor magnifies the risk of CVD by multiplying the risk rather than just having an additive effect [2][17][19].

Thorough analysis and understanding of the roles of all these factors would be important in the development and implementation of policies and strategies addressing CVD among Indigenous people. Such analysis is beyond the scope of this summary, however, which focuses on social and psychological factors, as well as the more proximal behavioural and biomedical risk factors.

Psycho-social factors

Relatively recent research has highlighted the important relationships between a variety of psycho-social factors and CVD. In particular, social isolation, depression, and lack of social support have now been acknowledged as factors independently associated with the causes and prognosis of CHD [20]. The risk contributed by these factors is recognised as of similar order to the conventional risk factors (cigarette smoking, high blood cholesterol and high blood pressure).

Indigenous people have been identified as an at-risk population whose social disadvantage is strongly associated with both psychosocial and conventional risk factors [20]. The acknowledgment of the equal importance of these psychosocial factors and the conventional risk factors has clear implications for the assessment and management of Indigenous people with CHD, and for public health policy and research.

Behavioural and biomedical risk factors

The risk factors summarised briefly in this section are smoking, physical inactivity, poor nutrition, overweight and obesity, and risky alcohol consumption. Information about high blood pressure among Indigenous people is provided in an earlier section of this summary.

Cigarette smoking

Tobacco smoking damages both the heart and blood vessels. The nicotine in tobacco smoke contributes to the development of atherosclerosis; the tar and carbon monoxide can cause increased heart rate, irregular heartbeats, increased blood pressure, and increase the risk of blood clots forming [2].

The 2004-2005 NATSIHS found that 51% of Indigenous people aged 18 years or older were current smokers, compared with 24% of non-Indigenous people [1]. For both populations, all except 2% of current smokers reported smoking daily. Similar proportions of Indigenous males and females reported smoking and, importantly, the proportions were high across all age groups. Overall, the proportion of Indigenous people living in remote areas who reported smoking (56%) was slightly higher than the proportion for those living in non-remote areas (49%). The levels documented in the 2004-2005 NATSIHS are similar to those reported from earlier similar surveys [1].

On the other hand, the 2007 National Drug Strategy Household Survey reported that 34% of Aboriginal and/or Torres Strait Islander people aged 14 years or older were current smokers [21]. Due to the relatively small sample size (23,356) and survey methodology, however, this is probably an under-estimate of the proportion of smokers in the Indigenous population.

Physical inactivity

Low levels of physical activity are an important contributor to the risk of developing CVD, particularly coronary/ischaemic heart disease, heart failure and stroke [2]. Benefits of regular physical activity are not only linked to a reduction in developing CVD, but in reducing some of the associated risk factors (such as overweight and obesity, hypertension, type 2 diabetes, and high levels of high-density lipoprotein and total blood cholesterol).

Based on self-reported results from the 2004-2005 NATSIHS, nearly half (49%) of Indigenous adults in non-remote areas had not participated in any physical activity during the two weeks prior to the survey [1]. Females and older people were more likely to be inactive than males.

Of Indigenous people living in non-remote areas who reported having CVD, 58% were physically inactive [1]. After adjusting for age, males and females had similar levels of inactivity. Physical inactivity increased with age, and almost three-quarters of people aged 65 years and over who had CVD were sedentary.

Poor nutrition

Poor nutrition has been linked to the development of various diseases, including coronary/ischaemic heart disease, stroke, hypertension, atherosclerosis and type 2 diabetes [2]. A high consumption of foods high in fat, especially saturated fatty acids, has been associated with an increased risk of conditions such as high blood pressure, high blood cholesterol levels, and overweight and obesity. Regular consumption of fruit and vegetables can reduce the risk of developing atherosclerosis, coronary heart disease and stroke, and can lower blood cholesterol and blood pressure levels [2].

The 2004-2005 NATSIHS reported that around 15% of Indigenous people did not eat fruit on a daily basis, 6% did not eat enough vegetables daily, and 3% did not eat enough fruit or vegetables daily [1]. These rates were higher in males, who were, after adjusting for age, 1.4 times more likely than women to not eat any fruit or vegetables daily.

Overweight and obesity

Overweight and obesity are associated with an increased risk of developing a range of diseases, such as coronary heart disease, stroke and type 2 diabetes [2]. Excess body fat also increases the prevalence of risk factors for heart disease, such as high blood pressure, high blood cholesterol and high levels of triglycerides.

The body mass index (BMI) is the most commonly used measure for classification of body weight, but it may not be suitable for all ethnic groups. There is increasing evidence that waist circumference or waist-to-hip ratio are more accurate in predicting cardiovascular risk [2][22] but BMI is the measure reported routinely by ABS and other surveys.

Based on self-reported height and weight measurements and after adjusting for survey non-response, the 2004-2005 NATSIHS reported that 60% of Indigenous adults were overweight, and 31% were obese (13% of whom were morbidly obese) [1]. Males were more likely to be overweight than females (1.1 times), but females were more likely to be obese (1.2 times). The prevalence of obesity, which generally increased with age, was high among those aged 45-64 years (39%) and 65 years and over (33%).

Risky alcohol consumption

Consumption of alcohol at levels considered to be harmful, particularly binge drinking, is associated with elevated blood pressure and triglyceride levels, and an increased risk of heart failure, stroke and abnormal heart rhythm. It can also contribute to obesity [2].

According to the 2004-2005 NATSIHS, about one-half of Indigenous people aged 18 years and over had not consumed alcohol in the week prior to the survey [1]. Of the remainder, 32% had consumed alcohol at levels considered of low risk, 16% at levels considered risky, and 8% at levels considered high risk.

Indigenous males reported drinking at risky levels 1.4 times more often than Indigenous females, and at high risk levels twice as often as females [2]. The proportions of risky alcohol consumption were highest among Indigenous males aged 35-44 years (24%). And Indigenous females aged 25-34 years (16%).

Summary

The cardiovascular health of Indigenous people is very much worse than that of other Australians, and CVD makes a substantial contribution to the disparity in health between Indigenous and non-Indigenous people.

Reflecting the higher levels of all the major cardiovascular conditions, mortality from CVD among Indigenous people is at least three times - and probably more than four times - higher than that of other Australians.

Coronary heart disease is the leading cause of death for Indigenous people, with the difference in death rates between Indigenous and non-Indigenous people being particularly high in the middle adult years (35-54 years). Cerebrovascular disease (including stroke) is another major contributor to Indigenous mortality, also having a much greater impact among Indigenous people than among non-Indigenous people in the middle adult years. Rheumatic heart disease, which is still responsible for a considerable number of deaths among Indigenous people, is now a very uncommon cause of death among non-Indigenous people.

The factors contributing to the high levels and mortality of CVD among Indigenous people are complex. The high levels of conventional behavioural and biomedical risk factors seen among Indigenous people are clearly associated with the high levels of CVD but these factors need to be considered in a 'social determinants of health' context.

As with other areas of Indigenous health, historical, socio-cultural and economic aspects are the 'upstream' factors within which the behavioural and biomedical risk factors and the actual impacts of CVD must be viewed.

References

1. Australian Bureau of Statistics (2006) National Aboriginal and Torres Strait Islander Health Survey: Australia, 2004-05. Canberra: Australian Bureau of Statistics
2. Australian Institute of Health and Welfare, Penm E (2008) Cardiovascular disease and its associated risk factors in Aboriginal and Torres Strait Islander peoples 2004-05. Canberra: Australian Institute of Health and Welfare
3. Australian Bureau of Statistics, Australian Institute of Health and Welfare (2008) The health and welfare of Australia's Aboriginal and Torres Strait Islander Peoples 2008. Canberra: Australian Bureau of Statistics and Australian Institute of Health and Welfare
4. Australian Institute of Health and Welfare (2009) Australian hospital statistics 2007-08. Canberra: Australian Institute of Health and Welfare
5. Australian Bureau of Statistics (1999) National Health Survey: Aboriginal and Torres Strait Islander results, Australia, 1995. Canberra: Australian Bureau of Statistics
6. Smith RM, Spargo RM, Hunter EM, King RA, Correll RL, Craig IH, Nestel PJ (1992) Prevalence of hypertension in Kimberley Aborigines and its relationship to ischaemic heart disease. Medical Journal of Australia; 156(Apr 20): 557-562
7. Leonard D, McDermott R, O’Dea K, Rowley KG, Pensio P, Sambo E, Twist A, Toolis R, Lowson S, Best JD (2002) Obesity, diabetes and associated cardiovascular risk factors among Torres Strait Islander people. Australian and New Zealand Journal of Public Health; 26(2): 144-149
8. Miller G, McDermott R, McCulloch B, Leonard D, Arabena K, Muller R (2002) The well person's health check: a population screening program in Indigenous communities in north Queensland. Australian Health Review; 25(6): 136-147
9. Bower C, Ramsay J (1994) Congenital heart disease: a 10 year cohort. Journal of Paediatrics and Child Health; 30: 414-418
10. Abeywardana S, Sullivan EA (2008) Congenital anomalies in Australia 2002–2003. Sydney: AIHW National Perinatal Statistics Unit
11. Bolisetty S, Daftary A, Ewald D, Knight B, Wheaton G (2004) Congenital heart defects in Central Australia. Medical Journal of Australia; 180(12): 614-617
12. Population Health Division (NSW) (2008) The health of the people of New South Wales – report of the Chief Health Officer, data book – Aboriginal peoples. Sydney: NSW Department of Health
13. Thrift AG, Hayman N (2007) Aboriginal and Torres Strait Islander peoples and the burden of stroke. International Journal of Stroke; 2(1): 57-59
14. Haysom L, Williams RE, Hodson EM, Lopez-Vargas P, Roy LP, Lyle DM, Craig JC (2009) Cardiovascular risk factors in Australian Indigenous and non-Indigenous children: a population-based study. Journal of Paediatrics and Child Health; 45(1-2): 20-27
15. National Health and Medical Research Council (2007) Cardiac rehabilitation geographic information system: geographic information system of cardiac rehabilitation services for Aboriginal and Torres Strait Islander peoples. Canberra: National Health and Medical Research Council
16. LehmanSJ, Baker RA, Aylward PE, Knight JL, Chew DP (2009) Outcomes of cardiac surgery in Indigenous Australians. Medical Journal of Australia; 190(10): 588-593
17. Hoy WE, Kondalsamy-Chennakesavan S, Wang Z (2007) Quantifying the excess risk for proteinuria, hypertension and diabetes in Australian Aborigines: comparison of profiles in three remote communities in the Northern Territory with those in the Ausdiab study. Australian and New Zealand Journal of Public Health; 31(2): 177-183
18. Mathur S, Moon L, Leigh S (2006) Aboriginal and Torres Strait Islander people with coronary heart disease: further perspectives on health status and treatment. Canberra: Australian Institute of Health and Welfare
19. Poulter N (1999) Coronary heart disease is a multifactorial disease. American Journal of Hypertension; 12(10, supp.1): 92-95
20. Bunker SJ, Colquhoun DM, Esler MD, Hickie IB, Hunt D, Jelinek VM, Oldenburg BF, Peach HG, Ruth D, Tennant CC, Tonkin AM (2003) "Stress" and coronary heart disease: psychosocial risk factors: National Heart Foundation of Australia position statement update. Medical Journal of Australia; 178(6): 272-276
21. Australian Institute of Health and Welfare (2008) National Drug Strategy Household Survey 2007 : detailed findings. Canberra: Australian Institute of Health and Welfare
22. Gracey M, Burke V, Martin DD, Johnston RJ, Jones T, Davis EA (2007) Assessment of risks of "lifestyle" diseases including cardiovascular disease and type 2 diabetes by anthropometry in remote Australian Aborigines. Asia Pacific Journal of Clinical Nutrition; 16(4): 688-697

Endnotes

i The numbers and ratios quoted in this summary have not been adjusted for the likely under-identification of Indigenous people in death registration systems. Based on the estimated level of Indigenous identification for Queensland, WA, SA, and the NT, the actual numbers and ratios could be up to 50% higher [ABS, Deaths Australia 2007].
ii As is the case with death data, the identification of Indigenous people in hospital data is incomplete, so caution must be exercised in the interpretation of the information presented here.
iii Diabetes and chronic kidney disease are both risk factors for cardiovascular disease as well as being diseases in their own right. Hypertension is a condition of the cardiovascular system, as well as a risk factor for other CVDs.

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