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1301.0 - Year Book Australia, 2008  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 07/02/2008   
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Contents >> Health >> Diabetes mellitus (Article)

FEATURE ARTICLE 2: DIABETES MELLITUS

Diabetes mellitus is a chronic condition in which the body is deficient in producing or using insulin. Untreated, people with diabetes have high blood glucose levels while their tissues lack nourishment. Diabetes can cause diseases of the eyes, kidneys, nerves and cardiovascular system, which can lead to a reduced quality of life and premature death. Type 2 diabetes, the most common form, has increased in prevalence since the 1980s, and further increases in obesity and physically inactive lifestyles, and the ageing of the population, have the potential to continue this increase.

Diabetes has been among conditions of concern to Australian health ministers for some time and continues to be a focus of the Council of Australian Governments' broader commitment to reducing the prevalence of avoidable chronic diseases and their risk factors. Internationally, there are fears that an epidemic of diabetes will follow changes in diet and lifestyle, and population ageing, in developing countries.

This article draws mainly on data from the 2004-05 National Health Survey (NHS), conducted by the Australian Bureau of Statistics (ABS). The survey scope was people in private dwellings. Data are self-reported estimates of people with diagnosed diabetes.

People with diabetes in the NHS are people who reported they currently had diabetes mellitus type 1 or type 2 or did not know the type they had. People who reported having gestational diabetes only, or diabetes insipidus (a rare form of diabetes unrelated to diabetes mellitus), were excluded.

Age standardising adjusts for differences in the age profiles of the populations being compared. In this article, age standardising is used to adjust for differences between people with and without diabetes in 2004-05, between different groups in the population in 2004-05, and between the Australian populations in 1995, 2001 and 2004-05, using as a basis the June 2001 estimated resident population.


Prevalence

In 2004-05, close to 700,000 people, or 3.5% of the population, reported they had diabetes (table 11.21). This was substantially higher than the 404,000 people, or 2.4% of the population, reporting it in 1995 (after age standardising the rate to adjust for age differences). This may reflect an increase in rates of diagnosis, rather than an increase in prevalence. Type 2 diabetes can go undiagnosed and an Australian study estimated that in 1999-2000, 7.5% of the population aged 25 years and over had diabetes mellitus, twice as many as had been diagnosed.

Type 2 is the most common type of diabetes. It is a degenerative condition in which the body tissue becomes resistant to insulin. In 2004-05, 83% of people with diabetes reported that they had this type. Type 2 most often develops in middle or older age and being overweight or physically inactive are important risk factors for this condition. Of those with type 2 in 2004-05, 81% had been aged 45 years or over when diagnosed. Most of the increase in the prevalence of diabetes since 1995 is due to an increase in type 2.

The less common type of diabetes is referred to as type 1 and is an autoimmune disease in which the body attacks and destroys the insulin producing cells. It has a relatively sudden onset and may arise in childhood, youth or later in life. At present there is no known way to reduce the risk of developing this disease. In 2004-05, 13% of people with diabetes reported they had type 1. The proportion of the population reporting type 1 remained the same over the period (0.5%) but there are some indications from other data sources of an increase in prevalence among children.

Some people have impaired glucose metabolism but not in the range that warrants a diagnosis of type 2 diabetes. These people are at higher risk of developing type 2 diabetes than other people, although lifestyle changes could often reduce this risk. An Australian study estimated that in 1999-2000, based on medical tests, 16% of the population aged 25 years and over (or 2 million people) had impaired glucose metabolism, mostly undiagnosed.
11.21 PEOPLE WITH DIABETES(a)

1995
2001
2004-05
Type of diabetes reported
no.
%
no.
%
no.
%

Type 1
79 500
0.5
95 200
0.5
91 900
0.5
Type 2
181 800
1.1
433 800
2.3
582 800
2.9
Type unknown
142 400
0.8
25 200
0.1
24 900
0.1
Total
403 700
2.4
554 200
3.0
699 600
3.5

(a) Age standardised to the estimated resident population at 30 June 2001.
Source: ABS data available on request, National Health Survey.


In 2004-05, the proportion of the population with diabetes increased with age from less than 0.5% of those aged under 25 years to 14% of those aged 65 years and over. A higher proportion of males than females had diabetes (4.0% compared with 3.2%), reflecting their higher rate of type 2 (3.4% compared with 2.6%). A similar proportion of males and females reported type 1 (0.5% compared with 0.4%).

There is interest in which population groups have higher rates of diabetes. In order to examine this variation, the following data are age standardised to adjust for differences in age structure between groups.

Health status often varies by socio-economic status. In 2004-05, people who lived in local areas rated as the most disadvantaged, based on characteristics such as income, employment and education, had higher rates of many long-term conditions, including diabetes (graph 11.22). The prevalence rate for diabetes was 2.3% in the least disadvantaged areas and increased to 5.4% in the most disadvantaged areas.

11.22 Diabetes prevalence(a), by relative disadvantage of area - 2004-05
Graph: 11.22 Diabetes prevalence(a), by relative disadvantage of area—2004–05

Diabetes and high blood sugar combined was 3.4 times as prevalent among Aboriginal and Torres Strait Islander peoples than among non-Indigenous people. Indigenous people living in remote areas of Australia had a rate of these conditions combined about twice that of Indigenous people living in non-remote areas. Diabetes is often referred to colloquially as blood sugar in remote Indigenous communities, and a combined type 1 and type 2 rate is used to compare the Indigenous and non-Indigenous populations.

Prevalence also varied by birthplace. Diabetes was least prevalent among people born in north-west Europe (2.7%) and most prevalent among people born in southern and central Asia (8.7%). Such variation can reflect differences in the prevalence of risk factors, but ethnicity is also considered to be a risk factor for diabetes, independent of other factors.


Risk factors

In the NHS, overweight and obesity are assessed using Body Mass Index (BMI), calculated from self-reported height and weight. (End note 1)

Being overweight is a recognised risk factor for type 2 diabetes. People may lose weight for health reasons after being diagnosed with diabetes. Nevertheless in 2004-05, the proportion of people who had diabetes increased from 2.8% of people who were of normal weight to 14% of those who were obese, with a BMI score of 40 or more (graph 11.23). Between 1995 and 2004-05, it became more common to be overweight, with overweight or obese people increasing from 43% to 51% of the population aged 15 years and over. The obese category increased the most, from 12% to 17% (see the article Overweight and obesity in adults).

11.23 Diabetes prevalence(a), by Body Mass Index(b) - 2004-05
Graph: 11.23 Diabetes prevalence(a), by Body Mass Index(b)—2004–05

Lack of exercise is also a risk factor for type 2 and in 2004-05, 5.0% of people who were sedentary in their leisure time had diabetes, compared with 4.1% of people who exercised at a low level, 3.7% of those who exercised at a moderate level and 2.7% of those who exercised at a high level. People who were sedentary in their leisure time made up 34% of the population aged 15 years and over in both 1995 and 2004-05.

People with hypertension are more likely than others to develop type 2 diabetes. This may be because diabetes and hypertension share risk factors such as physical inactivity and overweight. In 2004-05, nearly half of the population with diabetes (46%) reported having been diagnosed with hypertension. Similar proportions of the whole population reported they had hypertension in 1995 (11%) and 2004-05 (10%).

Gestational diabetes is a temporary form of diabetes experienced by 3-8% of pregnant women, and women who have had this condition are at increased risk of later developing type 2. In 2004-05, 101,600 women (who had not subsequently developed another type of diabetes) reported that they had had gestational diabetes or currently had it.


End note
      1. Body Mass Index (BMI) scores are calculated from reported height and weight information, using the formula: weight in kilograms divided by the height in metres squared. BMI values are grouped as follows: underweight (less than 18.5); normal weight (18.5 to less than 25.0); overweight (25.0 to less than 30.0) and obese (30.0 or higher).

      Self-reported height and weight may also differ from measured height and weight. In 1995, a comparison of these two methods suggested that when self-reporting, people tend to overstate their height and understate their weight. For further details, see How Australians Measure Up, 1995 (4359.0).


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