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Mortality and Morbidity: Diabetes
In 1995 about 430,700 (2.4%) Australians reported having diabetes at some time in their lives. This was slightly higher than the percentage of people reporting diabetes in 1989-90 (1.9% when adjusted to allow for the change in age distribution across the population). Diabetes was slightly more prevalent among women (2.5%) than men (2.3%), although gestational diabetes contributed 0.3 percentage points to the prevalence among women.
The prevalence of diabetes varied between the Australian-born and the overseas-born. Diabetes was more than twice as common among the overseas-born (4.1% compared to 1.9%), partly accounted for by their older age distribution. However, when age and sex differences are taken into account, the prevalence among the overseas-born was still higher (3.0%) than among the Australian-born (2.1%).
Diabetes mellitus moved from being the seventh to the sixth leading cause of death in 1996. The death rate was 15 deaths per 100,000 people, slightly higher than the death rate of 14 in 1995. The death rate for males was consistently higher than that for females (in 1996, 18 deaths per 100,000 compared to 12 deaths per 100,000). There were also many deaths where diabetes was mentioned as a contributing factor. If these deaths were included, diabetes contributed to about 50 deaths per 100,000 people in 1996.
PREVALENCE(a) OF DIABETES MELLITUS BY TYPE, 1995
Source: Unpublished data, 1995 National Health Survey.
Types of diabetes
People are far more likely to develop Type II diabetes than Type I. Of those reporting diabetes, 42% reported Type II, 18% Type I, and 6% gestational diabetes (excluding women who subsequently developed Type II). The remaining 33% did not know what type of diabetes they had, although the late onset and the type of medication used indicated that most of these had Type II.
Type I diabetes usually has an earlier onset than Type II. The majority (55%) of people with Type I were diagnosed when aged under 40, while 88% of those with Type II were diagnosed when aged 40 or over. Of those who did not know the type, 82% were diagnosed when aged 40 or over.
Diabetes mellitus is incurable at present. The prevalence of Types I and II diabetes in the population therefore increases with age. The prevalence of Type II in the population was low at ages under 40 and increased rapidly with greater age. Type I also increased with age, but compared to Type II there was a higher prevalence at younger ages and a less rapid increase after 40. Of those who did not know what type they had, the prevalence by age was more like that of Type II.
In those aged over 74, Type II appeared to decrease in prevalence whereas there was a further increase in prevalence where type was unknown. A greater proportion of people with diabetes in this age group did not know what type they had, compared to younger age groups. People who did not know what type they had made up 22% of those with diabetes aged under 15 and this proportion increased steadily with age to reach 43% of those aged over 74.
About 224,800 people had been diagnosed as having high sugar levels in their blood or urine at some time in their lives, but did not report a diagnosis of diabetes. Of these 16% (35,400) reported that they currently had high sugar levels. Some of these may actually have diabetes mellitus, as Type II is often known as a blood sugar condition.2
People at risk of diabetes
Health planners draw an important distinction between the two major types of diabetes mellitus, which have different causes and risk factors. Type I is thought to result from an auto-immune reaction which destroys the insulin producing cells. What triggers this reaction is unknown, although it is known that some people are at greater risk of Type I because of genetic factors.3
In contrast, Type II is a gradual deterioration in blood glucose regulation. Age and various lifestyle factors are thought to play an important role in the development of Type II. Identifying people at risk of Type II is a necessary part of planning health interventions for the condition. The diabetes research and education organisation, Diabetes Australia, identifies five main risk factors for Type II. These are being aged over 40, being overweight, having hypertension, giving birth to a baby weighing over 4 kg at birth (or having had gestational diabetes) and having a close relative with the disease.4 Diabetes Australia also recommends that anyone having three or more of these risk factors be tested for the disease.
The number of people with relatives with Type II is not known. However, some information is available on the other risk factors. In 1995, 5% of Australians (982,300 people) had the three risk factors (being aged over 40, overweight and hypertensive). Of these, 12% had been diagnosed with diabetes. However less than 1% of the remaining 862,100 people with these three risk factors had ever suspected they had diabetes and half of these had been tested.
In 1995, 27,000 women (who had not subsequently developed another form of diabetes), reported having had gestational diabetes. However, gestational diabetes often goes undetected. In addition, information on births in 1994 suggested that in that year alone 30,000 women gave birth to a baby weighing 4kg or more (about 12% of confinements).5 This indicates that there may be many more than 27,000 women at risk of developing Type II later in life.
Another risk factor for Type II diabetes is being an Indigenous Australian. Many studies suggest a higher prevalence in the Indigenous population than in the non-Indigenous, although data from the 1995 NHS on this topic is not yet available. Indigenous Australians may also be at risk of developing Type II at younger ages than are non-Indigenous Australians.6
People with diabetes were more likely to be overweight and sedentary than people without diabetes, but were less likely to drink alcohol or smoke. Of people aged over 14 who gave their height and weight, 74% of those with Type II were overweight, compared to 61% of those with Type I and 42% of those without diabetes. Part of this difference may be due to the older age profile of those with diabetes, although people with diabetes were more likely to be overweight than those without diabetes, in each age group examined.
People with diabetes are at greater risk of cardiovascular disease than those without diabetes. To reduce the risk of cardiovascular disease, exercise is recommended. However, people with diabetes were less likely to have exercised for sport or leisure than those without diabetes. Also, those who exercised tended to do so at a lower level. Of people with diabetes aged over 14, 41% were sedentary compared to 34% of those without diabetes. A further 36% exercised at a low level, 20% exercised at a moderate level and 2% exercised at a high level. In comparison, of people without diabetes, 34% exercised at a low level, 24% at a moderate level, and 8% at high level.
As well as being advised to exercise, people with diabetes are advised not to smoke, and to restrict alcohol intake. Of people with diabetes aged over 17, fewer reported drinking alcohol in the past two weeks or smoking regularly than people without diabetes. Even so, 37% of people with diabetes had drunk alcohol in the previous two weeks (compared to 56% of those without diabetes) and 18% were regular smokers (compared to 24% of people without diabetes).
There is an association between diabetes and other health conditions; especially conditions that affect the cardiovascular system, kidneys or eyes. Taken together, in 1995, 63% of people with diabetes had at least one of these conditions, compared to 17% of those without diabetes. The difference was substantial in all age groups.
The cardiovascular conditions hypertension, heart disease and stroke were the most commonly reported group of conditions for those with and without diabetes. However, they were more than four times more common for those with diabetes than those without. The proportion of people with at least one of these cardiovascular conditions increased with age for both groups. Hypertension was the most common cardiovascular condition, affecting 44% of those with diabetes and 10% of those without.
People with diabetes were more likely to have glaucoma or cataracts or to be blind than people without diabetes (17% compared to 3%). Cataracts were the most common of these eye conditions, affecting 10% of people with diabetes and 2% of those without. Blindness affected 6% of people with diabetes and 1% of those without. In those aged under 40, these eye conditions were relatively uncommon, but they were twice as likely in those with diabetes (1.4% compared to 0.5%). Between ages 40-64, 12% of people with diabetes had one of the eye conditions, compared to only 3% of those without. In those aged over 64, the eye conditions were more common, affecting a greater proportion of those with diabetes than those without (26% compared to 17%).
For people aged under 40 with diabetes, kidney disease was the second most common condition (after hypertension). Kidney disease was eight times more common in people with diabetes than in those without in this age group. Of those aged over 64, kidney disease was more than twice as common in those with diabetes.
Circulation problems and nerve damage mean that people with diabetes are prone to develop infections in their extremities. People with diabetes were more likely to have lost a limb than people without the disease (1.8% compared to 0.5%), although this was relatively uncommon for both groups.
SELECTED HEALTH CONDITIONS AMONG PEOPLE WITH DIABETES(a), BY AGE, 1995
Source: Unpublished data, 1995 National Health Survey.
1 World Health Organisation, 1985, Diabetes Mellitus: report of a WHO study group, World Health Organisation Technical Report Series 727, WHO, Geneva.
2 Phillips, P., Popplewell, P. 'Diabetes: what's new in Type II', Modern Medicine of Australia, July 1996.
3 McCarty, D. J., Zimmet, P., Dalton, A., Segal, L., Welborn, T. A., 1996, The Rise and Rise of Diabetes in Australia: a review of statistics, trends and costs, Diabetes Australia, Canberra.
4 Diabetes Australia, 1990, What is Diabetes?, information pamphlet; Diabetes Australia 1996, Facts on diabetes, fact sheet.
5 AIHW, National Perinatal Statistics Unit, 1997, Australia's Mothers and Babies 1994, Perinatal Statistics Series No. 5, National Perinatal Statistics Unit, Sydney.
6 Australian Bureau of Statistics, 1997, 1996 Causes of Death, cat. no. 3303.0, ABS, Canberra.
7 Guest, C. S., O'Dea, K., 1992, 'Diabetes in Aborigines and other Australian populations', Australian Journal of Public Health, vol. 16 No. 4.
8 Australian Bureau of Statistics, 1997, 1995 National Health Survey: Summary Results, cat. no. 4368.0, ABS, Canberra.