The findings of this study have shown that Aboriginal participants of the 45 and Up study are more likely to be younger, be socially disadvantaged, have a greater number of health risk factors, suffer from a range of medical conditions, have major physical disability, have severe functional health limitations and have high or very levels of psychological distress compared to the non-Aboriginal participants.
Similar to previous reports [6, 7], the largest disparity in health risk factors between the Aboriginal participants and the non-Aboriginal participants was found in current smoking rates and in BMI. Twenty-one percent of the Aboriginal participants were current regular smokers compared to 7% among non-Aboriginal participants. Although the reported prevalence of smoking among younger Aboriginal people is much higher [6, 7, 22], the relatively high proportion of smokers among ageing Aboriginal people in this study is of particular concern, due to their higher absolute risk of conditions such as cardiovascular disease. The proportion of non-drinkers of alcohol was greater among Aboriginal participants compared to non-Aboriginal participants. However, there was no significant difference between Aboriginal and non-Aboriginal participants in terms of those consuming ≥15 drinks per week, suggesting that those that did consume alcohol were more likely to be heavy drinkers.
The high proportion of Aboriginal participants of the 45 and Up study classified as ‘overweight’ or ‘obese’ was similar to previous reports [6, 7]. Aboriginal participants were twice as likely to be obese compared to non-Aboriginal participants. Although investigation of factors related to the high proportions of overweight and obese participants is beyond the scope of this paper, we did find that Aboriginal participants were less likely to have sufficient physical exercise and also had more sedentary time compared to non-Aboriginal participants. Further investigation of the relationship between diet and BMI may also elucidate some important factors associated with the high prevalence of obesity among Aboriginal participants of the 45 and Up study.
In keeping with the existing evidence, Aboriginal participants were more likely than non-Aboriginal participants to have ever been diagnosed with diabetes, stroke, depression, anxiety, heart disease and high blood pressure and were also more likely to have been diagnosed with multiple conditions during their lifetime. Of note, 16% and 35% of the Aboriginal participants reported not ever being diagnosed and not currently being treated for any of the conditions listed, respectively; hence, it is important to further investigate these individuals in future studies and determine the factors that are potentially associated with their ‘disease-free’ state. Highest level of formal education and income level were found to have the largest influence on the risk of Aboriginal-attributed risk of diabetes; adjustment for these factors attenuated the odds ratio for Aboriginal versus non-Aboriginal participants by 27% from 2.5 to 2.1. It is also important to note that history of ever being diagnosed with age-related chronic diseases such as diabetes, heart disease and high blood pressure peaked a decade earlier (60–69 years compared to 70–79 years) among Aboriginal participants compared to non-Aboriginal participants which reflects the younger age distribution of the Aboriginal population and the earlier onset of diseases among Aboriginal people.
A number of previous reports and studies have described the high levels of psychological distress among Aboriginal people [6, 7, 22, 23]. Furthermore, mental health disorders have been shown to be a significant contributor to the high burden of disease among the Aboriginal population . In the current study, 23% of Aboriginal participants had ever been diagnosed with depression during their lifetime. In addition, Aboriginal participants were also more likely than non-Aboriginal participants to have moderate, high and very high levels of psychological distress (with the disparity increasing with increasing severity) and were more likely to report that emotional problems had an impact on work and other activities. Also, a national report published by the AIHW showed that Aboriginal people with high/very levels of psychological distress were more likely to report fair/poor health and were also more likely to be daily smokers and consume high levels of alcohol .
Compared to non-Aboriginal participants, Aboriginal participants had five times the risk of reporting a work status of ‘disabled/sick,’ three times the risk of reporting a major physical disability (requiring help with daily tasks) and three times the risk of reporting severe physical functional limitations. This finding is in accordance to national data from the AIHW which show that the need for assistance with core activities was three times higher among Indigenous Australians compared to non-Indigenous Australians and was greatest in the 45–54 and 55–64 year age groups. Additionally, Aboriginal people were significantly more likely to be full-time carers for a sick or disabled family member or friend compared to non-Aboriginal people. Taken together, these indicators suggest that physical disability is a major problem among older Aboriginal people and their communities.
Although strong associations remained between Aboriginality and measures of health risk, ill health, psychological distress and disability in the fully adjusted models shown here, many of the associations examined were attenuated by around 11% to 66% following additional adjustment for highest level of formal education attained and income level. This suggests that lower levels of income and formal education are contributing to these associations, however there remains considerable proportions of the observed differences between Aboriginal and non-Aboriginal participants that are not explained by these factors.
Study strengths and limitations
The 45 and Up study includes data on a wide range of health-related factors from a large sample of middle-aged and older Aboriginal and non-Aboriginal participants from NSW. The inclusion of both Aboriginal and non-Aboriginal participants within the same cohort allows direct quantitative comparisons between the two groups. The current report is based on a cross-sectional survey of self-reported data; therefore, there are inherent limitations in determining causal relationships. The response rate of all participants (Aboriginal and non-Aboriginal) is estimated to be 18%. This means that the absolute prevalence reported here should be interpreted with caution. However, previous work has shown that internal comparisons, particularly the observed odds ratios, are likely to be reliable and generalisable more broadly . Moreover, the findings are comparable to previously conducted studies, suggesting that the potential biases are not having a large impact on the study results.
It was not possible to obtain specific response rates among Aboriginal participants since data on Aboriginal identification was available only among responders to the questionnaire. It is to be noted that the ability to complete the questionnaire in English may have preferentially selected participants with a higher level of formal education and of higher socio-economic status, compared to the general population.
An unweighted comparison of the 45 and Up study Aboriginal population to the NSW Indigenous population aged over 45 years (2006 NSW Census data available from the Australian Bureau of Statistics (ABS)) showed that the proportion of Aboriginal males and female study participants with a university degree or higher qualification was 2–3 times that of the Aboriginal people in the general population (4% compared to 12% in males (p < 0.0001), and 7% compared to 15% in females (p < 0.0001)). A higher proportion of study participants were married or in a de facto relationship than the general population (p < 0.0001), and the proportion of people needing help with core activities in the 65 and over age group was significantly lower in our sample (18% compared to 25%) (p = 0.002), but not across all relevant age groups aged 45 years and over (14% in both) (p = 0.65). The lower levels of major disability in older people are likely due to the method of data collection, as the 45 and Up Study required participants to complete the questionnaire themselves while the Census could be completed by another member of the household. Therefore, overall, it is possible that the health issues described in the study may be an underestimate of the true burden among Aboriginal people of NSW. However, even with the possibility of this bias, the large disparity observed in comparison to non-Aboriginal participants gives an indication of the levels of disease and disability among Aboriginal people.
Potential issues relating to data quality for the Aboriginal variable should also be considered when interpreting the results. The proportion of the cohort identifying as Aboriginal is low within the cohort, so the variable is more likely to be affected by issues such as random misclassification (for example, due to data entry errors or misunderstanding of the questionnaire item). Any such misclassification is likely to bias results towards the null, so would result in an underestimate of the underlying risks and relative risks. A program of work to validate the Aboriginal identification variables used in the 45 and Up Study is underway. Currently, there is a lack of clinical data available for this cohort, however, as the study progresses, data available will increase.
Study implications and areas for future research
Among the participants of this study, not only are Aboriginal people more likely to have a greater number of health risk factors and major medical conditions compared to non-Aboriginal people, high levels of physical disability and psychological distress also co-exist. A significant portion of the increased risk among Aboriginal participants was explained by level of formal education attained and income level. Educational attainment is an important indicator of socio-economic status since it remains stable throughout the life course after young adulthood and is usually established prior to employment and income level . Hence, promoting formal educational qualifications among Aboriginal people during their younger years which may potentially increase employment opportunities and thereby income level later in life may have a beneficial impact on long-term mental and physical health. However, the findings relating to income level should be interpreted more cautiously, since ill health can impact on income and hence be an effect, rather than a cause of illness.
Further examination of the factors associated with increased morbidity among the 45 and Up Aboriginal participants and follow-up data will provide more insight into ways of preventing the high morbidity and premature mortality among Aboriginal people. Findings of this study also suggest that greater attention may be needed towards addressing social inequalities in health in Australia and providing appropriate mental health services and disability support for Aboriginal people. Given that Aboriginal participants of this study were significantly younger than the non-Aboriginal participants, it is also important to tailor health policies and support services for ageing Aboriginal people in accordance to this younger age distribution.