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Measuring Prevalence: Obesity, diabetes and associated cardiovascular risk factors among Torres Strait Islander people

Measuring Prevalence: Obesity, diabetes and associated cardiovascular risk factors among Torres... Abstract Objective: T descr ibe the lifestyle-related o chronic disease and risk factor prevalence among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area Health Ser vice District and to compare this information with that available for the general Australian population. Methods: Voluntar y community-based screening for persons aged 15 years and older, including oral glucose tolerance test, anthropometry, health questionnaire, measurement of lipids and lipoprotein levels, blood pressure and urinar y albumin to creatinine ratio. Results: Nine communities par ticipated in screening between 1993 and 1997. Five hundred and ninety-two participants (286 male and 306 female) identified as Torres Strait Islander. There were high prevalences of overweight (30%), obesity (51%), abdominal obesity (70%), diabetes (26%), hypercholesterolaemia (33%), albuminuria (28%), hypertension (32%) and tobacco smoking (45%). Only 8.5% of men and 6.5% of women were free of any cardiovascular risk factors (abdominal obesity, hypercholesterolaemia, hyper tension, dyslipidaemia, smoking, diabetes, albuminuria). Comparisons of this information for T orres Str ait Islander people with results from the AusDiab survey show rates of obesity three times higher and diabetes six times higher than for other Australians. Conclusions: There is a very high prevalence of preventable chronic disease and associated risk factors among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area. Implications: Effective interventions to prevent and manage obesity, diabetes and associated cardiovascular risk factors are essential if the health of the Torres Strait Islander people is to improve. Such interventions could inform initiatives to stem the burgeoning epidemic of obesity and diabetes among all Australians. ( Aust N Z J Public Health 2002; 26: 144-9) Dympna Leonard and Robyn McDermott Queensland Health, Tropical Public Health Unit, Cairns, Queensland Kerin O’Dea Menzies School of Health Research, Northern Territory Kevin G. Rowley The University of Melbourne, Department of Medicine, St Vincent’s Hospital, Victoria Poi Pensio and Edna Sambo Queensland Health, Torres Strait and Northern Peninsula Area Health Service District, Queensland Aletia Twist, Raima Toolis and Simone Lowson formerly Queensland Health, Torres Strait and Nor thern Peninsula Area Health Service Distr ict, Queensland James D. Best The University of Melbourne, Department of Medicine, St Vincent’s Hospital, Victoria iabetes associated with obesity was first reported among people of the Torres Strait in the medical literature in 1961.1 A study perfor med in the late 1970s repor ted diabetes prevalence of 19% in the outer islands and 13% in the Thursday Island and Nor thern Peninsula Area (NPA).2 The community-based health screening repor ted here was initiated in response to the need for up-to-date health information identif ied by community leaders at a health planning meeting early in 1993.3 The Tor res Strait and Northern Peninsula Area Health Ser vice District (see Map 1) includes the islands of the Tor res Strait as well as the Northern Peninsula Area on the tip of Cape York on the mainland. According to the 1996 Census,4 there were 8,531 people living in the Tor res Strait and Norther n Peninsula Area of whom 6,850 (80%) identif ied as Indigenous, that is being of Tor res Strait Islander, Aboriginal, or of mixed Aboriginal and Torres Strait Islander descent. Of this number, 83%, or 5,667 people, identify as Torres Strait Islanders. There are 16 Torres Strait Islander communities on 15 outer islands and f ive communities in the NPA, three of which identify as Aboriginal and two as Tor res Strait Islander. In addition to these, a large proportion of the population live on Thursday Island and adjacent islands of the Thursday Island group. Sur veys were conducted in nine communities between September 1993 and Ma y 1997 at the request of local Health Action Groups and/or community councils. This report describes the prevalence of diabetes and cardiovascular disease (CVD) risk factors in the 592 Tor res Strait Islander people who participated in the screening. Submitted: October 2000 Revision requested: July 2001 Accepted: March 2002 Correspondence to: D. Leonard, Tropical Public Health Unit, PO Box 1103, Cair ns, Queensland 4870. Fax: (07) 4050 3662; e-mail: Dympna_Leonard@health.qld.gov.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH VOL. 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people Map 1: The Torres Strait and Northern Peninsula Area Health Service District. Methods Par ticipation in the surveys was voluntary and was offered to all residents aged 15 years and older. The guidelines set out by the National Health and Medical Research Council of Australia regarding research in Indigenous communities were followed. The Ethics Committee of the former Queensland Health Peninsula and Torres Strait Regional Health Authority gave ethical approval. The results of these surveys were reported back to the people of the Tor res Strait and Northern Peninsula Area by way of individual reports to participants, repor ts to each community and (with the exception of the 1997 sur vey) a summary report to the Torres Strait and Northern Peninsula Area Diabetes Summit in June 1996. Recruitment A preliminary community consultation was conducted prior to each survey. The survey was conducted in a central location in each community, starting early each morning to f acilitate participation while f asting. Recruitment activities by community health staff and the sur vey team, prior to and during the surveys, were supported by use of health centre records and local knowledge to identify all eligible residents and encourage par ticipation. subjects, with diabetic status conf irmed by fasting blood glucose measurement with a glucometer, did not receive a glucose tolerance test. Fasting blood samples were collected into fluorideheparin (for glucose), lithium-heparin and serum tubes (for lipids). Circulating concentrations of glucose, cholesterol and triglycerides were assayed using standard enzymatic techniques (BoehringerMannheim, Mannheim, FRG) on a Hitachi 705 or 704 autoanalyser. High density lipoprotein (HDL) was isolated by precipitation of other lipoproteins with 15% polyethylene glycol (MW 6000). The following criteria were used to def ine abnormalities of circulating lipids: • Hypercholesterolaemia; fasting total cholesterol ≥5.5 mmol/ L.6 • Dyslipidaemia; fasting HDL cholesterol <1.0 mmol/L plus fasting triglycerides ≥2.0 mmol/L.7 Albumin:creatinine ratio (ACR) was measured in early morning urine samples. Microalb uminuria was def ined as ACR in the range 3.4 to less than 34 mg/mmol and macroalbuminuria as ACR equal to or greater than 34 mg/mmol.8 Anthropometric measurements Body weight was recorded to the nearest 0.1 kg (UC300 digital electronic scales; A.N.D., Tokyo, Japan) and height to the nearest 0.1 cm (Harpenden anthropometer; Holtain Ltd, Crymych, UK). The criterion used to def ine overweight was Body Mass Index (BMI) 25 to less than 30 kg/m2 and obesity BMI equal to or greater than 30 kg/m2.9 Waist and hip circumferences were measured to the nearest 0.1 cm. High waist-to-hip ratio (WHR) was def ined as g reater than 0.90 for men and 0.80 for women.10 Biochemical analysis and diagnostic criteria Oral glucose tolerance tests (75 g glucose monohydrate) were performed early in the mor ning after a minimum of eight hours fasting. Impaired glucose tolerance (IGT), impaired fasting glucose (IFG) and diabetes are reported here according to World Health Organization 1999 criteria;5 diabetes, fasting plasma glucose ≥7.0 mmol/L and/or 2 h post glucose load plasma glucose ≥11.1 mmol/L and/or cur rent hypoglycaemic mediation; IGT, fasting plasma glucose less than 7.0 mmol/L and 2 h plasma glucose 7.8 to 11.0 mmol/L; IFG, fasting plasma glucose 6.0 to 6.9 mmol/ L and 2 h plasma glucose less than 7.8 mmol/L. Known diabetic 2002 VOL. 26 NO . 2 Blood pressure and lifestyle information Sitting blood pressure was measured using a Dinamap model 8100 automated blood pressure monitor (Critikon; Tampa FL, US) AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Leonard et al. Article Table 1: Prevalence (%) of CVD risk factors, stratified by g ender and age. Women ≥ 35yr 15-34yr Overweight Obesity High waist:hip ratio IGT Diabetes Hyper tension Hypercholesterolaemia Dyslipidaemia Microalbuminur ia Macroalbuminuria Smoking Dr inking Exercise Notes: (a) Within gender p≤0.005 between age groups. (b) Within gender p<0.05 between age groups. Men 15-34yr All ≥35yr 34.9 53.4b 89.7a 7.5 23.7 67.3a 94.2a 5.1 55.7a 50.0a 39.1a 28.2a 30.8a 20.5a 30.6b 26.6a 59.8 32.0a 53.7a 46.3a 37.9a 29.2a 9.7b 45.2a 53.7a 52.8a with the subject seated for at least five minutes prior to measurement. The mean of three consecutive readings was taken. Hypertension was def ined as systolic blood pressure ≥140 mmHg and/ or diastolic blood pressure ≥90 mmHg and/or current anti-hypertensive medication.11 Participants were asked if they currently smoked tobacco or drank alcohol. Participants were asked about usual physical activity practices and were defined as being physically active if they participated in any physical activity vigorous enough to increase breathing rate at least three times a week for at least 20 minutes each time. Table 2: Risk factor prevalence (%) stratified by diabetes status and gender. Non-diabetic Women n Obesity Hypertension Hypercholesterolaemia Dyslipidaemia Microalbuminuria Macroalbumin uria Smoking Men n Obesity Hypertension Hypercholesterolaemia Dyslipidaemia Microalbuminuria Macroalbumin uria Smoking Diabetic pa Statistical analysis The Australian Bureau of Statistics, Census of Housing and Population,4 1996 (CData software) was used to describe the study population in the calculation of denominator numbers and in the calculation of age-adjusted prevalence rates (see Tables 2 and 3). The Torres Strait and Northern Peninsula Area Health Ser vice District is represented by one statistical local area (Torres). Statistical analysis w as undertaken using the Statistical Package for Social Sciences (SPSS) version 10 and EpiInfo version 6. The statistical procedures used in this research included summary statistics, standard chi-squared analyses (see Tab le 1) and Mantel-Haenszel age-weighted chi-square test for trend analysis (see Table 2). Age-adjusted prevalences from the sample were compared with those from the AusDiab12 survey by the use of indirectly standardised ratios (ISRs).13 All reported p-values are two-sided and were considered to be significant where p-value was <0.05. 0.048 <0.001 0.484 0.002 0.004 0.032 0.519 Notes: Data are age-adjusted using the overall sur vey sample as the reference population. (a) Age-weighted Mantel-Haenszel chi-square test. Results Response ranged from 33% to 67% of the eligible Indigenous residents. Eighty per cent of participants identified as Torres Strait Islander (286 men and 306 women), 9.5% as Aboriginal and 10.2% as mixed Aboriginal and Torres Strait Islander descent. The results reported here refer onl y to those 592 participants who identif ied as Torres Strait Islander. Approximately 50% of the eligible Torres Strait Islander people in the nine communities participated. The survey sample comprised approximately 17% of the Torres Strait Islander population over 15 years of the district. The sur vey sample did not differ significantly from the district Indigenous VOL. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people population with respect to gender (52% women in both cases) or age distribution (p=0.432 for women, p=0.131 for men).2 The age of Torres Strait Islander participants ranged from 15 years to 85 years for men and from 15 years to 87 years for women. The prevalence of cardiovascular risk factors for men and women are shown in Table 1. More than 80% of people were either overweight or obese. The prevalence of obesity substantially exceeded the prevalence of overweight in both men and women. Overall, 51% of people were obese and 30% were overweight. Mean BMI for women was 31.5 (SD 6.9, range 18.3-55.8) and for men 29.7 (SD 5.6, range 18.8-54.9). Obesity and abdominal obesity were significantly more common in older compared with younger men and women. Among younger people, the prevalence of overweight (p=0.607) and obesity (p=0.412) was not signif icantly different between men and women. Among older people, overweight was more common in men (p=0.032) and obesity more common in women ( p=0.014). Prevalence of abdominal obesity was particularly high with rates among younger (p<0.001) but not older (p=0.148) women exceeding those of men. Twenty-six point two per cent of people had diabetes, 4.7% impaired glucose tolerance and 69.1% normal glucose tolerance. IGT was significantly more common in older compared with younger men but not among older compared with younger women. Diabetes was more common among older people in both men and women. Among younger people, the prevalence of IGT (p=0.015) but not diabetes (p=0.131) was significantly more common among women than men. Among older people, the prevalence of diabetes (p<0.001) b ut not IGT (p =0.148) was significantly more common among women than among men. Hypertension was high among older men and older women. While the prevalence of hypertension among younger women was relatively low, among young men hypertension was signif icantly higher (p<0.005). The prevalence of raised cholesterol and dyslipidaemia was high among older people, particularl y older men. Hypercholesterolaemia and dyslipidaemia were significantly more common in older compared with younger men and women (see Table 1). Among younger people, the prevalence of hypercholesterolaemia (p=0.050) was signif icantly more common among men than among women, while dyslipidaemia was more prevalent among young women than among young men (p=0.016). Among older people, there was no signif icant difference in prevalence of hypercholesterolaemia (p=0.208) or dyslipidaemia (p=0.073) between men and women. However, both younger men and younger women had levels of raised cholesterol and dyslipidaemia consistent with increased risk of CVD. Micro- and macro- albuminuria were more prevalent among older compared with younger men and women (see Table 1). However, younger men and women also exhibited significant levels of microalbuminuria. The prevalence of microalbuminuria did not differ by sex in either age group. Among older, but not younger, people, macroalbuminuria was more common in women (p=0.010). Smoking was highly prevalent, with about 45% of the sample 2002 VOL. 26 NO . 2 Table 3: Comparison of age-adjusted prevalences from the AusDiab14 survey and the Torres Study using indirectly standardised ratios (ISR). Prevalence (%) ISR (95% CI) Torres Strait AusDiab Islanders Obesity IFG IGT Diabetes Hypercholesterolaemia LDL chol. ≥3.5 mmol/L HDL chol. <1.0 mmol/L Triglycerides ≥2.0 mmol/L Hyper tension Current smoking 55.7 2.9 5.6 33.1 37.2 51.3 52.9 41.2 39.2 39.4 19.5 5.1 8.8 5.6 47.7 43.0 11.9 19.0 22.7 16.9 2.9 (2.5-3.2) 0.6 (0.4-0.9) 0.6 (0.4-0.9) 6.2 (5.3-7.3) 0.8 (0.7-0.9) 1.2 (1.0-1.4) 4.4 (3.9-5.0) 2.2 (1.9-2.5) 1.8 (1.6-2.1) 2.3 (2.0-2.7) being cur rent smokers. Smoking prevalence was significantly higher among younger people (see Table 1) and among men in both age groups. Low levels of regular physical activity were reported for more than half the survey sample in all age and sexspecific categories, except for young men who were significantly more likely to be active than were older men (see Table 1) or younger women (p<0.001). Approximately half the par ticipants drank alcohol, with older people and especially older women more likely to be abstainers. After adjusting for age, most cardiovascular risk f actors (obesity, abdominal obesity hypertension, and dyslipidaemia) were , more prevalent among people with diabetes than among those who were non-diabetic (see Table 2). Hypercholesterolaemia was not associated with diabetes either for men or for women. Unlike women, in men diabetes was not associated with g reater prevalence of microalbuminuria but was associated with prevalence of macroalb uminuria. Six point five per cent of women and 8.5% of men had no cardiovascular risk factors (see F igure 1) and 44.5% of women and 49.8% of men had three or more co-existing risk f actors. Table 3 shows comparison of risk factor prevalence among the 212 Torres Strait Islander men and 231 women in this study who were age 25 years and older, with the AusDiab12 study of the general Australian population, 1999-2000. Data in Table 3 have been age-adjusted using the Indigenous population (25 years and older) of the Torres Strait as a reference population as population data by age is not available for Torres Strait Islander people only but is available for Indigenous people (those who identify as Aboriginal or Torres Strait Islander or as both Aboriginal and Torres Strait Islander). While obesity is close to three times more prevalent among Torres Strait Islander people compared with other Australians, diabetes is more than six times as prevalent. The prevalence of both impaired glucose tolerance and impaired fasting glucose was signif icantly lower among Torres Strait Islander people. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Leonard et al. Article Hypertension was more prevalent among Torres Strait Islander people. There are differences also in the prevalence of lipid disorders: raised cholesterol is more prevalent in the general Australian population but raised triglygerides and low levels of high density lipoproteins are more prevalent among Torres Strait Islanders. Smoking was more than twice as common among the Torres Strait Islanders than the general population. Figure 1: Prevalence of co-existing risk factors* within an individual for women and men. *Risk factors included are abdominal obesity hypertension, , hypercholesterolaemia, dyslipidaemia, diabetes, micro- or macro-albuminuria and smoking. 30% 25% prevalence 20% 15% 10% 5% 0% 0 1 2 3 4 5+ number of co-existing risk factors Female Male Discussion The high prevalence of obesity reported here among Torres Strait Islanders is similar to that reported for Torres Strait Islander participants in the National Aboriginal and Torres Strait Islander Survey.14 Comparison with the AusDiab infor mation for the general Australian population highlights the higher prevalence of obesity among Torres Strait Islanders. Associated with this is the higher prevalence of diabetes, particularly among Torres Strait Islander women. While obesity is three times more prevalent among Torres Strait Islanders, diabetes is six times more prevalent. This dispropor tionate burden of diabetes may reflect the ‘dose-response relationship’ between BMI and the risk of developing diabetes15 as both the prevalence and the degree of obesity are particularly high among Torres Strait Islander people. Conversely, the prevalence of IGT and IFG is relatively low among Torres Strait Islander people compared with other Australians, which perhaps reflects that these two populations are at different stages in the epidemic of obesity and diabetes. The high prevalence of obesity and diabetes among women in the Torres Strait has, in addition to the impact on their own health, a potential intergenerational impact on the health of their children.16 Much attention in recent years has focused on the inter relationship of under-nutrition in early life and chronic disease in adult life.17 However, less frequently discussed is the inter-relationship of over-nutrition in early life and chronic disease in adult life. The children of mothers who were diabetic during pregnancy or who subsequently developed diabetes have a marked amplif ication of risk of early onset obesity and diabetes.18,19 This intergenerational effect probably contributes to the increasingly high prevalence and early onset of diabetes in populations where obesity and diabetes are already prevalent. Indeed, Type 2 diabetes has been diagnosed in primary school-aged children in the Torres Strait in recent y ears.20 As in other populations, the prevalence of co-morbidities such as hyper tension, dyslipidaemia and renal disease was higher among people who had diabetes, but the high prevalence of these other risk factors among those Torres Strait Islanders who were not diabetic is particularly striking. The high prevalence of hypertension among young men is notable and may be related to the high prevalence of drinking among this group. Hypercholesterolaemia was less common than reported in the AusDiab study, consistent with data from other Indigenous Australian populations.21 In contrast, low levels of HDL cholesterol and high levels of triglycerides were very common. The high prevalence of smoking and the low levels of physical activity contribute to the poor health demonstrated here. Poor nutrition, at148 tributable in part to limited access to healthy food, 22 compounds the negative effects of smoking and low levels of physical activity. A limitation of the present study is that both the communities that participated in these surveys and the individuals who participated in each community were self-selected. Therefore, the question remains as to how representative the results are of the population of Tor res Strait and the Northern Peninsula Area. Anecdotal information attributed low par ticipation to internal community politics, religious beliefs and, in one location, concerns about the Human Genome project rather than to health characteristics of attenders and non-attenders. The results shown here are congruent with routinely collected health data for the Torres Strait and NP Health Ser vices District that show high levels of hospiA tal separation for diabetes, particularly for women, and excess mortality for diabetes for both men and women compared with Queensland.23 Furthermore, the present survey sample was indistinguishable from the district population with respect to age and gender distribution. Subsequent to these surveys, a simplified annual adult health check has been developed which is being incorporated into routine health services in the Torres Strait and Northern Peninsula Areas Health Ser vice District. This check, supported by a computer-based management system, will provide representative routine health information in the future. The epidemic of obesity and diabetes among people of the Torres Strait is a relatively recent phenomenon. The rise in prevalence of obesity, diabetes and associated conditions has often been attributed to genetic susceptibility exposed when people assume a Western lifestyle.24 More recent research points to the potent intergenerational effect of abnormal glucose tolerance in mothers18,19 as contributing to the familial pattern of inheritance, while VOL. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people the influence of social determinants25 on health are increasingly recognised as contributing to inequalities in health that become self-perpetuating across the generations.26 Such research highlights the need for interventions to address the non-genetic factors contributing to the poor health profile of Tor res Strait Islander people as described here. Food supply issues, especially access to good-quality fresh fruit and vegetables, and lifestyle behaviours must be addressed. Access to education and employment opportunities are also needed. The Torres Strait Diabetes Summit in 1996 led to the development of Meriba Zageth for Diabetes – Our Work for Diabetes, an integrated strategy to address the pre vention, early detection and management of diabetes. A review of Meriba Zageth four years later identified that w hile progress had been made in the clinical areas of early detection and management of diabetes, little progress had been achieved in prevention components of the strategy.27 Substantial investment in expertise and resourcing of preventative strategies is required if the problem of chronic disease among Torres Strait Islander people is to be reduced. It is ironic that the gap between the health status of Torres Strait Islander people and other Australians may be diminishing, not because of improved health in the Torres Strait b ut because of the burgeoning epidemic of obesity and diabetes among Australians in general.12 Recent reports have highlighted that intensive interventions to improve nutrition and physical activity among people at high risk of diabetes can reduce or delay progression to diabetes.28-30 The application of such research among Torres Strait Islander people would provide experience and expertise which, as well as contributing to equity for Indigenous people, will be of value in addressing a health issue of increasing concer n to all Australians. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australian and New Zealand Journal of Public Health Wiley

Measuring Prevalence: Obesity, diabetes and associated cardiovascular risk factors among Torres Strait Islander people

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Wiley
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Copyright © 2002 Wiley Subscription Services
ISSN
1326-0200
eISSN
1753-6405
DOI
10.1111/j.1467-842X.2002.tb00907.x
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Abstract

Abstract Objective: T descr ibe the lifestyle-related o chronic disease and risk factor prevalence among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area Health Ser vice District and to compare this information with that available for the general Australian population. Methods: Voluntar y community-based screening for persons aged 15 years and older, including oral glucose tolerance test, anthropometry, health questionnaire, measurement of lipids and lipoprotein levels, blood pressure and urinar y albumin to creatinine ratio. Results: Nine communities par ticipated in screening between 1993 and 1997. Five hundred and ninety-two participants (286 male and 306 female) identified as Torres Strait Islander. There were high prevalences of overweight (30%), obesity (51%), abdominal obesity (70%), diabetes (26%), hypercholesterolaemia (33%), albuminuria (28%), hypertension (32%) and tobacco smoking (45%). Only 8.5% of men and 6.5% of women were free of any cardiovascular risk factors (abdominal obesity, hypercholesterolaemia, hyper tension, dyslipidaemia, smoking, diabetes, albuminuria). Comparisons of this information for T orres Str ait Islander people with results from the AusDiab survey show rates of obesity three times higher and diabetes six times higher than for other Australians. Conclusions: There is a very high prevalence of preventable chronic disease and associated risk factors among Torres Strait Islander people of the Torres Strait and Northern Peninsula Area. Implications: Effective interventions to prevent and manage obesity, diabetes and associated cardiovascular risk factors are essential if the health of the Torres Strait Islander people is to improve. Such interventions could inform initiatives to stem the burgeoning epidemic of obesity and diabetes among all Australians. ( Aust N Z J Public Health 2002; 26: 144-9) Dympna Leonard and Robyn McDermott Queensland Health, Tropical Public Health Unit, Cairns, Queensland Kerin O’Dea Menzies School of Health Research, Northern Territory Kevin G. Rowley The University of Melbourne, Department of Medicine, St Vincent’s Hospital, Victoria Poi Pensio and Edna Sambo Queensland Health, Torres Strait and Northern Peninsula Area Health Service District, Queensland Aletia Twist, Raima Toolis and Simone Lowson formerly Queensland Health, Torres Strait and Nor thern Peninsula Area Health Service Distr ict, Queensland James D. Best The University of Melbourne, Department of Medicine, St Vincent’s Hospital, Victoria iabetes associated with obesity was first reported among people of the Torres Strait in the medical literature in 1961.1 A study perfor med in the late 1970s repor ted diabetes prevalence of 19% in the outer islands and 13% in the Thursday Island and Nor thern Peninsula Area (NPA).2 The community-based health screening repor ted here was initiated in response to the need for up-to-date health information identif ied by community leaders at a health planning meeting early in 1993.3 The Tor res Strait and Northern Peninsula Area Health Ser vice District (see Map 1) includes the islands of the Tor res Strait as well as the Northern Peninsula Area on the tip of Cape York on the mainland. According to the 1996 Census,4 there were 8,531 people living in the Tor res Strait and Norther n Peninsula Area of whom 6,850 (80%) identif ied as Indigenous, that is being of Tor res Strait Islander, Aboriginal, or of mixed Aboriginal and Torres Strait Islander descent. Of this number, 83%, or 5,667 people, identify as Torres Strait Islanders. There are 16 Torres Strait Islander communities on 15 outer islands and f ive communities in the NPA, three of which identify as Aboriginal and two as Tor res Strait Islander. In addition to these, a large proportion of the population live on Thursday Island and adjacent islands of the Thursday Island group. Sur veys were conducted in nine communities between September 1993 and Ma y 1997 at the request of local Health Action Groups and/or community councils. This report describes the prevalence of diabetes and cardiovascular disease (CVD) risk factors in the 592 Tor res Strait Islander people who participated in the screening. Submitted: October 2000 Revision requested: July 2001 Accepted: March 2002 Correspondence to: D. Leonard, Tropical Public Health Unit, PO Box 1103, Cair ns, Queensland 4870. Fax: (07) 4050 3662; e-mail: Dympna_Leonard@health.qld.gov.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH VOL. 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people Map 1: The Torres Strait and Northern Peninsula Area Health Service District. Methods Par ticipation in the surveys was voluntary and was offered to all residents aged 15 years and older. The guidelines set out by the National Health and Medical Research Council of Australia regarding research in Indigenous communities were followed. The Ethics Committee of the former Queensland Health Peninsula and Torres Strait Regional Health Authority gave ethical approval. The results of these surveys were reported back to the people of the Tor res Strait and Northern Peninsula Area by way of individual reports to participants, repor ts to each community and (with the exception of the 1997 sur vey) a summary report to the Torres Strait and Northern Peninsula Area Diabetes Summit in June 1996. Recruitment A preliminary community consultation was conducted prior to each survey. The survey was conducted in a central location in each community, starting early each morning to f acilitate participation while f asting. Recruitment activities by community health staff and the sur vey team, prior to and during the surveys, were supported by use of health centre records and local knowledge to identify all eligible residents and encourage par ticipation. subjects, with diabetic status conf irmed by fasting blood glucose measurement with a glucometer, did not receive a glucose tolerance test. Fasting blood samples were collected into fluorideheparin (for glucose), lithium-heparin and serum tubes (for lipids). Circulating concentrations of glucose, cholesterol and triglycerides were assayed using standard enzymatic techniques (BoehringerMannheim, Mannheim, FRG) on a Hitachi 705 or 704 autoanalyser. High density lipoprotein (HDL) was isolated by precipitation of other lipoproteins with 15% polyethylene glycol (MW 6000). The following criteria were used to def ine abnormalities of circulating lipids: • Hypercholesterolaemia; fasting total cholesterol ≥5.5 mmol/ L.6 • Dyslipidaemia; fasting HDL cholesterol <1.0 mmol/L plus fasting triglycerides ≥2.0 mmol/L.7 Albumin:creatinine ratio (ACR) was measured in early morning urine samples. Microalb uminuria was def ined as ACR in the range 3.4 to less than 34 mg/mmol and macroalbuminuria as ACR equal to or greater than 34 mg/mmol.8 Anthropometric measurements Body weight was recorded to the nearest 0.1 kg (UC300 digital electronic scales; A.N.D., Tokyo, Japan) and height to the nearest 0.1 cm (Harpenden anthropometer; Holtain Ltd, Crymych, UK). The criterion used to def ine overweight was Body Mass Index (BMI) 25 to less than 30 kg/m2 and obesity BMI equal to or greater than 30 kg/m2.9 Waist and hip circumferences were measured to the nearest 0.1 cm. High waist-to-hip ratio (WHR) was def ined as g reater than 0.90 for men and 0.80 for women.10 Biochemical analysis and diagnostic criteria Oral glucose tolerance tests (75 g glucose monohydrate) were performed early in the mor ning after a minimum of eight hours fasting. Impaired glucose tolerance (IGT), impaired fasting glucose (IFG) and diabetes are reported here according to World Health Organization 1999 criteria;5 diabetes, fasting plasma glucose ≥7.0 mmol/L and/or 2 h post glucose load plasma glucose ≥11.1 mmol/L and/or cur rent hypoglycaemic mediation; IGT, fasting plasma glucose less than 7.0 mmol/L and 2 h plasma glucose 7.8 to 11.0 mmol/L; IFG, fasting plasma glucose 6.0 to 6.9 mmol/ L and 2 h plasma glucose less than 7.8 mmol/L. Known diabetic 2002 VOL. 26 NO . 2 Blood pressure and lifestyle information Sitting blood pressure was measured using a Dinamap model 8100 automated blood pressure monitor (Critikon; Tampa FL, US) AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Leonard et al. Article Table 1: Prevalence (%) of CVD risk factors, stratified by g ender and age. Women ≥ 35yr 15-34yr Overweight Obesity High waist:hip ratio IGT Diabetes Hyper tension Hypercholesterolaemia Dyslipidaemia Microalbuminur ia Macroalbuminuria Smoking Dr inking Exercise Notes: (a) Within gender p≤0.005 between age groups. (b) Within gender p<0.05 between age groups. Men 15-34yr All ≥35yr 34.9 53.4b 89.7a 7.5 23.7 67.3a 94.2a 5.1 55.7a 50.0a 39.1a 28.2a 30.8a 20.5a 30.6b 26.6a 59.8 32.0a 53.7a 46.3a 37.9a 29.2a 9.7b 45.2a 53.7a 52.8a with the subject seated for at least five minutes prior to measurement. The mean of three consecutive readings was taken. Hypertension was def ined as systolic blood pressure ≥140 mmHg and/ or diastolic blood pressure ≥90 mmHg and/or current anti-hypertensive medication.11 Participants were asked if they currently smoked tobacco or drank alcohol. Participants were asked about usual physical activity practices and were defined as being physically active if they participated in any physical activity vigorous enough to increase breathing rate at least three times a week for at least 20 minutes each time. Table 2: Risk factor prevalence (%) stratified by diabetes status and gender. Non-diabetic Women n Obesity Hypertension Hypercholesterolaemia Dyslipidaemia Microalbuminuria Macroalbumin uria Smoking Men n Obesity Hypertension Hypercholesterolaemia Dyslipidaemia Microalbuminuria Macroalbumin uria Smoking Diabetic pa Statistical analysis The Australian Bureau of Statistics, Census of Housing and Population,4 1996 (CData software) was used to describe the study population in the calculation of denominator numbers and in the calculation of age-adjusted prevalence rates (see Tables 2 and 3). The Torres Strait and Northern Peninsula Area Health Ser vice District is represented by one statistical local area (Torres). Statistical analysis w as undertaken using the Statistical Package for Social Sciences (SPSS) version 10 and EpiInfo version 6. The statistical procedures used in this research included summary statistics, standard chi-squared analyses (see Tab le 1) and Mantel-Haenszel age-weighted chi-square test for trend analysis (see Table 2). Age-adjusted prevalences from the sample were compared with those from the AusDiab12 survey by the use of indirectly standardised ratios (ISRs).13 All reported p-values are two-sided and were considered to be significant where p-value was <0.05. 0.048 <0.001 0.484 0.002 0.004 0.032 0.519 Notes: Data are age-adjusted using the overall sur vey sample as the reference population. (a) Age-weighted Mantel-Haenszel chi-square test. Results Response ranged from 33% to 67% of the eligible Indigenous residents. Eighty per cent of participants identified as Torres Strait Islander (286 men and 306 women), 9.5% as Aboriginal and 10.2% as mixed Aboriginal and Torres Strait Islander descent. The results reported here refer onl y to those 592 participants who identif ied as Torres Strait Islander. Approximately 50% of the eligible Torres Strait Islander people in the nine communities participated. The survey sample comprised approximately 17% of the Torres Strait Islander population over 15 years of the district. The sur vey sample did not differ significantly from the district Indigenous VOL. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people population with respect to gender (52% women in both cases) or age distribution (p=0.432 for women, p=0.131 for men).2 The age of Torres Strait Islander participants ranged from 15 years to 85 years for men and from 15 years to 87 years for women. The prevalence of cardiovascular risk factors for men and women are shown in Table 1. More than 80% of people were either overweight or obese. The prevalence of obesity substantially exceeded the prevalence of overweight in both men and women. Overall, 51% of people were obese and 30% were overweight. Mean BMI for women was 31.5 (SD 6.9, range 18.3-55.8) and for men 29.7 (SD 5.6, range 18.8-54.9). Obesity and abdominal obesity were significantly more common in older compared with younger men and women. Among younger people, the prevalence of overweight (p=0.607) and obesity (p=0.412) was not signif icantly different between men and women. Among older people, overweight was more common in men (p=0.032) and obesity more common in women ( p=0.014). Prevalence of abdominal obesity was particularly high with rates among younger (p<0.001) but not older (p=0.148) women exceeding those of men. Twenty-six point two per cent of people had diabetes, 4.7% impaired glucose tolerance and 69.1% normal glucose tolerance. IGT was significantly more common in older compared with younger men but not among older compared with younger women. Diabetes was more common among older people in both men and women. Among younger people, the prevalence of IGT (p=0.015) but not diabetes (p=0.131) was significantly more common among women than men. Among older people, the prevalence of diabetes (p<0.001) b ut not IGT (p =0.148) was significantly more common among women than among men. Hypertension was high among older men and older women. While the prevalence of hypertension among younger women was relatively low, among young men hypertension was signif icantly higher (p<0.005). The prevalence of raised cholesterol and dyslipidaemia was high among older people, particularl y older men. Hypercholesterolaemia and dyslipidaemia were significantly more common in older compared with younger men and women (see Table 1). Among younger people, the prevalence of hypercholesterolaemia (p=0.050) was signif icantly more common among men than among women, while dyslipidaemia was more prevalent among young women than among young men (p=0.016). Among older people, there was no signif icant difference in prevalence of hypercholesterolaemia (p=0.208) or dyslipidaemia (p=0.073) between men and women. However, both younger men and younger women had levels of raised cholesterol and dyslipidaemia consistent with increased risk of CVD. Micro- and macro- albuminuria were more prevalent among older compared with younger men and women (see Table 1). However, younger men and women also exhibited significant levels of microalbuminuria. The prevalence of microalbuminuria did not differ by sex in either age group. Among older, but not younger, people, macroalbuminuria was more common in women (p=0.010). Smoking was highly prevalent, with about 45% of the sample 2002 VOL. 26 NO . 2 Table 3: Comparison of age-adjusted prevalences from the AusDiab14 survey and the Torres Study using indirectly standardised ratios (ISR). Prevalence (%) ISR (95% CI) Torres Strait AusDiab Islanders Obesity IFG IGT Diabetes Hypercholesterolaemia LDL chol. ≥3.5 mmol/L HDL chol. <1.0 mmol/L Triglycerides ≥2.0 mmol/L Hyper tension Current smoking 55.7 2.9 5.6 33.1 37.2 51.3 52.9 41.2 39.2 39.4 19.5 5.1 8.8 5.6 47.7 43.0 11.9 19.0 22.7 16.9 2.9 (2.5-3.2) 0.6 (0.4-0.9) 0.6 (0.4-0.9) 6.2 (5.3-7.3) 0.8 (0.7-0.9) 1.2 (1.0-1.4) 4.4 (3.9-5.0) 2.2 (1.9-2.5) 1.8 (1.6-2.1) 2.3 (2.0-2.7) being cur rent smokers. Smoking prevalence was significantly higher among younger people (see Table 1) and among men in both age groups. Low levels of regular physical activity were reported for more than half the survey sample in all age and sexspecific categories, except for young men who were significantly more likely to be active than were older men (see Table 1) or younger women (p<0.001). Approximately half the par ticipants drank alcohol, with older people and especially older women more likely to be abstainers. After adjusting for age, most cardiovascular risk f actors (obesity, abdominal obesity hypertension, and dyslipidaemia) were , more prevalent among people with diabetes than among those who were non-diabetic (see Table 2). Hypercholesterolaemia was not associated with diabetes either for men or for women. Unlike women, in men diabetes was not associated with g reater prevalence of microalbuminuria but was associated with prevalence of macroalb uminuria. Six point five per cent of women and 8.5% of men had no cardiovascular risk factors (see F igure 1) and 44.5% of women and 49.8% of men had three or more co-existing risk f actors. Table 3 shows comparison of risk factor prevalence among the 212 Torres Strait Islander men and 231 women in this study who were age 25 years and older, with the AusDiab12 study of the general Australian population, 1999-2000. Data in Table 3 have been age-adjusted using the Indigenous population (25 years and older) of the Torres Strait as a reference population as population data by age is not available for Torres Strait Islander people only but is available for Indigenous people (those who identify as Aboriginal or Torres Strait Islander or as both Aboriginal and Torres Strait Islander). While obesity is close to three times more prevalent among Torres Strait Islander people compared with other Australians, diabetes is more than six times as prevalent. The prevalence of both impaired glucose tolerance and impaired fasting glucose was signif icantly lower among Torres Strait Islander people. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Leonard et al. Article Hypertension was more prevalent among Torres Strait Islander people. There are differences also in the prevalence of lipid disorders: raised cholesterol is more prevalent in the general Australian population but raised triglygerides and low levels of high density lipoproteins are more prevalent among Torres Strait Islanders. Smoking was more than twice as common among the Torres Strait Islanders than the general population. Figure 1: Prevalence of co-existing risk factors* within an individual for women and men. *Risk factors included are abdominal obesity hypertension, , hypercholesterolaemia, dyslipidaemia, diabetes, micro- or macro-albuminuria and smoking. 30% 25% prevalence 20% 15% 10% 5% 0% 0 1 2 3 4 5+ number of co-existing risk factors Female Male Discussion The high prevalence of obesity reported here among Torres Strait Islanders is similar to that reported for Torres Strait Islander participants in the National Aboriginal and Torres Strait Islander Survey.14 Comparison with the AusDiab infor mation for the general Australian population highlights the higher prevalence of obesity among Torres Strait Islanders. Associated with this is the higher prevalence of diabetes, particularly among Torres Strait Islander women. While obesity is three times more prevalent among Torres Strait Islanders, diabetes is six times more prevalent. This dispropor tionate burden of diabetes may reflect the ‘dose-response relationship’ between BMI and the risk of developing diabetes15 as both the prevalence and the degree of obesity are particularly high among Torres Strait Islander people. Conversely, the prevalence of IGT and IFG is relatively low among Torres Strait Islander people compared with other Australians, which perhaps reflects that these two populations are at different stages in the epidemic of obesity and diabetes. The high prevalence of obesity and diabetes among women in the Torres Strait has, in addition to the impact on their own health, a potential intergenerational impact on the health of their children.16 Much attention in recent years has focused on the inter relationship of under-nutrition in early life and chronic disease in adult life.17 However, less frequently discussed is the inter-relationship of over-nutrition in early life and chronic disease in adult life. The children of mothers who were diabetic during pregnancy or who subsequently developed diabetes have a marked amplif ication of risk of early onset obesity and diabetes.18,19 This intergenerational effect probably contributes to the increasingly high prevalence and early onset of diabetes in populations where obesity and diabetes are already prevalent. Indeed, Type 2 diabetes has been diagnosed in primary school-aged children in the Torres Strait in recent y ears.20 As in other populations, the prevalence of co-morbidities such as hyper tension, dyslipidaemia and renal disease was higher among people who had diabetes, but the high prevalence of these other risk factors among those Torres Strait Islanders who were not diabetic is particularly striking. The high prevalence of hypertension among young men is notable and may be related to the high prevalence of drinking among this group. Hypercholesterolaemia was less common than reported in the AusDiab study, consistent with data from other Indigenous Australian populations.21 In contrast, low levels of HDL cholesterol and high levels of triglycerides were very common. The high prevalence of smoking and the low levels of physical activity contribute to the poor health demonstrated here. Poor nutrition, at148 tributable in part to limited access to healthy food, 22 compounds the negative effects of smoking and low levels of physical activity. A limitation of the present study is that both the communities that participated in these surveys and the individuals who participated in each community were self-selected. Therefore, the question remains as to how representative the results are of the population of Tor res Strait and the Northern Peninsula Area. Anecdotal information attributed low par ticipation to internal community politics, religious beliefs and, in one location, concerns about the Human Genome project rather than to health characteristics of attenders and non-attenders. The results shown here are congruent with routinely collected health data for the Torres Strait and NP Health Ser vices District that show high levels of hospiA tal separation for diabetes, particularly for women, and excess mortality for diabetes for both men and women compared with Queensland.23 Furthermore, the present survey sample was indistinguishable from the district population with respect to age and gender distribution. Subsequent to these surveys, a simplified annual adult health check has been developed which is being incorporated into routine health services in the Torres Strait and Northern Peninsula Areas Health Ser vice District. This check, supported by a computer-based management system, will provide representative routine health information in the future. The epidemic of obesity and diabetes among people of the Torres Strait is a relatively recent phenomenon. The rise in prevalence of obesity, diabetes and associated conditions has often been attributed to genetic susceptibility exposed when people assume a Western lifestyle.24 More recent research points to the potent intergenerational effect of abnormal glucose tolerance in mothers18,19 as contributing to the familial pattern of inheritance, while VOL. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 26 NO. 2 Measuring Prevalence Cardiovascular risk factors among Torres Strait Islander people the influence of social determinants25 on health are increasingly recognised as contributing to inequalities in health that become self-perpetuating across the generations.26 Such research highlights the need for interventions to address the non-genetic factors contributing to the poor health profile of Tor res Strait Islander people as described here. Food supply issues, especially access to good-quality fresh fruit and vegetables, and lifestyle behaviours must be addressed. Access to education and employment opportunities are also needed. The Torres Strait Diabetes Summit in 1996 led to the development of Meriba Zageth for Diabetes – Our Work for Diabetes, an integrated strategy to address the pre vention, early detection and management of diabetes. A review of Meriba Zageth four years later identified that w hile progress had been made in the clinical areas of early detection and management of diabetes, little progress had been achieved in prevention components of the strategy.27 Substantial investment in expertise and resourcing of preventative strategies is required if the problem of chronic disease among Torres Strait Islander people is to be reduced. It is ironic that the gap between the health status of Torres Strait Islander people and other Australians may be diminishing, not because of improved health in the Torres Strait b ut because of the burgeoning epidemic of obesity and diabetes among Australians in general.12 Recent reports have highlighted that intensive interventions to improve nutrition and physical activity among people at high risk of diabetes can reduce or delay progression to diabetes.28-30 The application of such research among Torres Strait Islander people would provide experience and expertise which, as well as contributing to equity for Indigenous people, will be of value in addressing a health issue of increasing concer n to all Australians.

Journal

Australian and New Zealand Journal of Public Health – Wiley

Published: Jan 1, 2002

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