Cardiovascular Risk and Type 2 Diabetes Mellitus in Indigenous Australians

Chan, Lionel C. K. (2007). Cardiovascular Risk and Type 2 Diabetes Mellitus in Indigenous Australians PhD Thesis, School of Medicine, The University of Queensland.

       
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Author Chan, Lionel C. K.
Thesis Title Cardiovascular Risk and Type 2 Diabetes Mellitus in Indigenous Australians
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2007-01
Thesis type PhD Thesis
Supervisor Shaw, Joanne
West, Malcolm J.
Language eng
Subjects 321003 Cardiology (incl. Cardiovascular Diseases)
321004 Endocrinology
Abstract/Summary Coronary heart disease is the single greatest contributor to mortality within developed countries in our time. Type 2 diabetes mellitus and obesity, both of which are potent risk factors for coronary heart disease, are common conditions with rapidly rising rates of prevalence both globally and in Australia. Within Australia, Indigenous Australians suffer from disproportionately high rates of diabetes, obesity and coronary heart disease, the reason for which lies, in part, with changes in dietary intake and decreased levels of physical activity over the past 200 years. These disease trends have led to a substantially reduced life expectancy from an increase in excess cardiovascular deaths in Indigenous Australians. Assessment of cardiovascular risk in Indigenous Australians is complicated by ethnic differences in cardiovascular risk factors and their prevalence. There is also evidence that Indigenous Australians are genetically predisposed to diabetes. Current cardiovascular risk stratification algorithms are suboptimal, significantly underestimating risk in Indigenous Australians. This thesis aimed to address these issues. Firstly, to evaluate the efficacy of a lifestyle intervention programme to sustainably improve markers of health outcome in a cohort of Indigenous Australians who were overweight or had type 2 diabetes mellitus by improving diet and physical activity levels. Secondly, to evaluate the utility of anthropometric markers of obesity, ultrasound markers of atherosclerotic burden and serum C-reactive protein as additional cardiovascular risk stratification tools. The Healthy Lifestyle Programme (HELP) was a two year prospective intervention study designed and implemented with substantial input from the Indigenous community. The primary intervention consisted of a series of educational workshops delivered predominantly by Indigenous health workers advocating improving diet and increasing physical activity. To complement these workshops, facilities were established within the community to support dietary improvement and increased physical activity. Sustainable changes to markers of cardiovascular outcome, including significant reductions in central obesity and blood pressure were demonstrated over time. A slowing in the deterioration of renal function as marked by albuminuria was also detected. These beneficial changes were accompanied by increased physical activity and improved dietary intake. In a substudy, individuals with the apolipoprotein E4 genotype, who were dyslipidaemic at baseline, benefited from lipid profiles that improved significantly during the course of the study. Changes in blood pressure and central obesity detected during the course of the project are likely to have significant clinical impact on health outcomes considering their sustained nature. Evaluating ultrasound imaging based markers of cardiovascular risk, carotid artery intimal medial thickness was a more reliable measure of risk based on its firm correlation with established cardiovascular risk factors compared to brachial artery flow mediated vasodilatation. Carotid artery intimal medial thickness may be the better surrogate marker to improve cardiovascular risk stratification in the Indigenous population. Examining anthropometric markers of obesity, body mass index and waist circumference but not waist hip ratio correlated well with traditional cardiovascular risk factors. Furthermore, both body mass index and waist circumference predicted insulin resistance fairly well using threshold values derived from receiver operating characteristics curve analyses. Both body mass index and waist circumference were simple to perform with a high degree of reproducibility between observers and will likely be valuable additional cardiovascular risk stratification tools. Raised inflammatory stress, as marked by elevated serum C-reactive protein levels, was found in individuals with diabetes or obesity. C-reactive protein levels did not correlate with carotid artery intimal medial thickness, suggesting that C-reactive protein raises cardiovascular risk by means other than increasing atherosclerotic burden. Genotyping a small random sample of our the C-reactive protein gene promoter region. This SNP was found to independently increase serum C-reactive protein in the Framingham cohort. A genetic basis for increased inflammatory stress may contribute to coronary heart disease in Indigenous Australians. In summary, a community centred lifestyle intervention programme was efficacious in producing sustainable improvement in markers of health outcome. Examination of additional cardiovascular risk markers in the Indigenous community have provided evidence for using carotid artery intimal medial thickness, waist circumference, body mass index and serum C-reactive protein levels to improve cardiovascular risk stratification. These additional tools would allow for more specific resource allocation to target individuals at highest cardiovascular risk for preventative management. C-reactive protein gene polymorphisms, their contribution to circulating C-reactive protein levels and cardiovascular outcomes warrants further investigation in the Indigenous population. A more proactive risk management plan, which includes a lifestyle intervention component, may yield the greatest improvement in long term health outcomes if targeted at younger members of the Indigenous community.
Keyword Cardiovascular risk
Type 2 diabetes mellitus
Indigenous Australians
Obesity
Lifestyle intervention

 
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