Leanness and type 2 diabetes in a population of indigenous Australians

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Abstract

Objective

To determine the prevalence of type 2 diabetes and its risk factors in a population of indigenous Australians.

Research design and methods

A cross-sectional study of 332 indigenous community residents aged 15 years and over with fasting blood samples and anthropometric measurements.

Results

Almost half of the study population (47.3%) was extremely lean (BMI < 22 kg/m2). Leanness was particularly pronounced in the youngest age group (15 < 20 years), 78% of which had a BMI < 22 kg/m2. The prevalence of diabetes was 12%. It was highest in those 45–54 years and declined in older aged people. No cases of diabetes were detected in those aged less than 30 years. Diabetes prevalence was strongly linked to BMI and age (age-adjusted odds ratio = 24.1, 95% CI 6.0–96.5, p < 0.001) for BMI  25 kg/m2 versus BMI < 22 kg/m2. Those with the lowest diabetes risk profile are lean (BMI < 22 kg/m2) and/or young (age 15–34 years).

Conclusions

These results highlight that strategies to prevent or delay the onset of diabetes should focus on the maintenance of leanness from adolescence and throughout adult life whilst young people are still in the process of forming lifelong habits.

Introduction

There is no evidence that diabetes and related disorders occurred among indigenous Australians prior to colonisation [1], [2], [3]. Type 2 diabetes and other preventable chronic diseases are increasing among indigenous Australians and they, rather than infant mortality, explain the much lower life expectancy relative to the overall Australian population [4]. Studies among different indigenous populations in Northern Australia since the early 1980s have reported crude diabetes prevalence rates ranging from 4.5 [5] to 21% [6] compared to 8% in men and 6.8% in women for the Australian population [7]. These crude rates are misleading and underestimate the excess frequency of diabetes, particularly among younger age groups [8]. For example, Wang et al. [9] reported a 12-fold higher prevalence of diabetes in the 25–34 years age group in a Northern Australian indigenous community relative to the Australian population.

The risk of type 2 diabetes is strongly linked with obesity [10], [11] and both are recent phenomena among indigenous Australians [12]. There is, however, considerable variation in the prevalence of diabetes and prevalence of overweight and obesity within and between different indigenous populations. Historical documents repeatedly comment on the leanness, agility and physical strength of indigenous Australians. Early anthropological studies conducted among Aboriginal people, invariably reported mean Body Mass Index (BMI) < 20 kg/m2 and no increase in BMI with age [1]. O’Dea et al. [13] reported a mean BMI of 16.7 kg/m2 with no commonly reported risk factors for diabetes or cardiovascular disease among a small group of Aboriginal people living “a traditionally oriented lifestyle” on their ancestral land in North East Arnhemland. Increasing levels of overweight/obesity and diabetes in both indigenous and non-indigenous Australians now present a public health challenge.

As part of a community based intervention to reduce the risk of chronic disease, the prevalence of diabetes and related risk factors were measured in an Arnhemland community to identify target groups for community initiatives to reduce risk of diabetes. This paper describes the survey methods and the association between diabetes and body size.

Section snippets

Study population

The study community, the largest in North East Arnhemland, is on an island approximately 550 km from Darwin and has a centralised population of approximately 1500. There are more than 20 language groups and English is a third or fourth language for most people. The population is very mobile as people move between the community and surrounding homelands or other communities to maintain strong relationships with land and family. The Aboriginal land rights (Northern Territory) Act of 1976 granted

Results

Anthropometric measurements and a fasting blood sample were collected from 332 of the 706 residents aged 15 years or older identified in the house to house census. The study population was representative of the census population in terms of gender distribution. However, proportionately more older women (≥35 years) participated than any other age group (p = 0.01, Table 1).

Almost half of the study population (47.3%) was lean (BMI < 22 kg/m2), 30.4% were overweight (BMI  25  30 kg/m2) and 7.5% obese (BMI  

Discussion

The relative leanness of the population, particularly among young people is the striking finding in this study. The BMI pattern of the study population tended to bi-modality in many age groups rather than resembling a normal distribution. The overall mean BMI was low, but this did not reflect the variation by age, and in particular the high level of overweight and obesity in the middle-aged.

There was no case of diabetes among people <30 years but the prevalence of diabetes rose sharply

Acknowledgements

Many people have contributed invaluably to this study: Community members and community based researchers: Steven Djati Yunupingu (dec) and Heather Ganilawur; Galiwin’ku Community Council, Charlie Yunupingu, Alfred Wunbaya, Mike Newton (dec); Ngalkanbuy Health Service: Cherryl Wirtanen, Joan Djamalaka, Cameron Main and Andrew Knight; the diabetes screening planning committee: Keith Djiniyini, Ian Gumbula, Dorothy Wanamula, Stephanie Yikaniwuy and Litia Vuqa; Menzies School of Health Research:

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