National Statistics and Opportunities for Improved Surveillance,
Prevention, and Control

DIABETES AND ABORIGINAL PEOPLES

(taken from the Background Paper for the Development of an Aboriginal Diabetes Strategy: Report of the Working Group, draft, June 17, 1998, with permission of the Health Programs Analysis Division, First Nations and Inuit Health Programs, Medical Services Branch, Health Canada.)

FIGURE 23
Diabetes by age group: First Nations, 1991

* Caution: high sampling variability for this figure.
Data from 1991 Aboriginal Peoples Survey, for people who self-identify as North American Indian.
Source: Bobet, 1997, Medical Services Branch.

Prevalence of Diabetes

• Diabetes Rates Are Very High Among Aboriginal Peoples

  The age-standardized prevalence of diabetes among Aboriginals is at least three times that of the general population^(23,24). A series of studies have documented high rates in First Nations communities, and although much less is known about diabetes among Métis people, results from the Aboriginal Peoples Survey suggest that rates are well above the non-Aboriginal average. Inuit people are the only exception to the pattern: at present, their rates are below the national average; however, there are indications that they are rising, and it is feared that over time they will be as high as those of the other Aboriginal groups. Further, since not everyone with diabetes knows about it or has been given the diagnosis, existing figures probably understate the true prevalence of diabetes, possibly by as much as one half⁽²⁵⁾.

  According to a 1991 Statistics Canada report, the prevalence of diabetes among native groups in Canada is as follows: 8.5% of North American Indian peoples on Indian reserves and settlements; 5.3% of North American Indian peoples off reserves; 5.5% of Métis people; 1.9% of Inuit people⁽²⁶⁾.

• Most Aboriginal Peoples with Diabetes Are Women

  Approximately two-thirds of the First Nations people with a diagnosis of diabetes are women⁽²⁴⁾.

• Diabetes Rates Vary Substantially Across the Country

  Diabetes rates vary from province to province, and from community to community. This means that in some areas rates are far more than triple the national average, whereas in others they are lower. According to the 1991 Aboriginal Peoples Survey, the provincial rates were lowest in British Columbia and the northern territories and highest in the Ontario-Manitoba-Saskatchewan areas⁽²⁴⁾.

• The Prevalence of Diabetes Is Increasing

  Until the 1940s, diabetes was virtually unknown among Aboriginal peoples^(26,27). Statistical data are lacking, since few groups have been continuously monitored longitudinally for any length of time. However, a 1983 study in the Sioux Lookout Zone showed a prevalence rate of 2.8%. By 1994, this had risen to 3.8%, with nearly 45% of the cases having been diagnosed in the preceding five years^(28,29). For chronic illnesses of long duration, such as diabetes, the prevalence can be expected to increase over time as a function of incidence, survival of people with diabetes, and aging of the population. In Manitoba, it has been estimated that the number of Aboriginal diabetes cases can be expected to increase threefold over the next 20 years⁽³⁰⁾.

  Complications of Diabetes

  Given that many complications take 10-20 years to develop, and that diabetes is a relatively new condition for Aboriginal peoples, it is not surprising that there are gaps in the literature about the types, onset and severity of complications faced by Aboriginal peoples in Canada. The existing literature suggests the following description.

  FIGURE 24
  Presence of one or more complications*: First Nations,
  1991, by age group and presence of diabetes

• 
  
  * People reporting that they have one or more of: high blood pressure, heart disease, vision problems.
  Data from 1991 Aboriginal Peoples Survey. Refers to people who identify as "North American Indian". Source: Bobet, 1997, Medical Services Branch.

• Increased Risk of Cardiovascular Disease (heart disease)

  People with diabetes have a substantially increased risk of developing cardiovascular disease^(24,31). Among Status Aboriginals in Manitoba, almost 60% of hospitalizations for heart disease and approximately half of the hospitalizations for stroke occurred among people with diabetes⁽³²⁾. In Kahnawake, half of those with diabetes had significant heart disease leading to heart attacks and coronary bypass surgery⁽³³⁾.

• Higher Prevalence of Hypertension (high blood pressure)

  The prevalence of hypertension is far higher among First Nations adults with diabetes: 43% compared with just 10% of those without diabetes. Untreated hypertension has been identified as an additional risk factor for cardiovascular disease such as heart attacks and strokes, and for kidney disease and retinopathy.

• Increased Risk of Stroke

  Studies have established that people with diabetes are at increased risk of having strokes, possibly because many people with diabetes also suffer from hypertension⁽³¹⁾. A study at Kahnawake (Quebec) found that 13% of people with diabetes had had strokes, versus just 3% of a comparable group of people without diabetes. This gave an odds ratio of 4.5⁽³³⁾. The same study found that the risk of having macrovascular disease was six times higher among people with diabetes. These ratios are comparable to those observed in the non-Aboriginal population.

• More Lower Limb Amputations

  People with diabetes have a 15 times greater risk of requiring lower extremity amputation than those without diabetes. Those more than 40 years of age whose diabetes was diagnosed at least 10 years earlier are at the highest risk⁽³⁴⁾. A study of Native Americans in Oklahoma showed that the mean interval to first amputation was 6.6 years after the diagnosis⁽³⁵⁾. Yet if individuals at risk are aggressively sought out and treated, up to 50% of amputations can be prevented⁽³⁴⁾.

  In general, morbidity and mortality rates are elevated among individuals with diabetes who have undergone an amputation. For the Native Americans in Oklahoma, the 5-year survival rate after first amputation was only 40%⁽³⁵⁾.

• Higher Rates of Kidney Disease and Dialysis - Especially for Aboriginal Peoples with Diabetes

  Whiteside⁽³⁶⁾ documents that the prevalence of diabetic nephropathy is much higher among Aboriginal Canadians than the general population with diabetes. The rates range from 25 to 60% after 15 to 20 years with diabetes. In Manitoba, it is estimated that an Aboriginal person is 12 times more likely to have diabetic nephropathy than a non-Aboriginal. The risk of end-stage renal disease (ESRD) is approximately four times that of other Manitobans, and more than half of this ESRD is caused by diabetes.

  Among Aboriginal peoples with ESRD, the relative risk of undergoing dialysis is 6.5 times that of a non-Aboriginal patient (Dr. K.N. Bernstein, Central Dialysis Unit, Manitoba: personal communication, 1998). Among First Nations people living in Manitoba, there has been an increase in dialysis starts of more than 400% since 1987⁽³²⁾.

• Higher Rates of Eye Disease

  Diabetes causes diabetic retinopathy, which is the leading cause of adult-onset blindness in North American adults. People with diabetes also have higher rates of cataracts. The National Institutes of Health in the United States indicates that approximately half those with diabetes have some form of eye disease, and just over 10% report serious retinal disease. In the Pima of Arizona, however, serious retinopathy has a frequency rate of 18%⁽²⁷⁾, and at Kahnawake (Quebec) 50% of patients had retinopathy after 10 to 15 years of the disease⁽³³⁾.

• Frequent Instances of Peripheral Neuropathy

  Diabetes can affect the nervous system. This manifests as an absence of reflexes and impaired nerve conduction, and usually involves pain and decreased sensation in the lower limbs. Estimates of how common this is among people with diabetes vary enormously, and none are specific to Aboriginal peoples.

  Groups Needing Special Focus in Diabetes Initiatives

  In addition to the general trends described, the impact of diabetes on specific subpopulations warrants attention.

• Children - Instances of Aboriginal Children with a Diagnosis of Type 2 Diabetes

  Although Type 2 diabetes is referred to as "adult-onset", in recent years it has been diagnosed in Aboriginal children as young as 5 to 8 years of age in both northern Ontario⁽³⁷⁾ and Manitoba⁽³⁸⁾. Furthermore, the incidence appears to be increasing at a rapid rate⁽³⁹⁾. In Manitoba, the number of Aboriginal children with a diagnosis of diabetes rose from 20 in 1990 to 51 in 1995. There was a similar pattern in the Sioux Lookout Zone: in 1994, diabetes was diagnosed in 18 children (under age 16), and in 1997 in 52 children (under age 18). In both these areas, girls outnumbered boys by more than five to one among the children with this condition.

  Because duration of high blood sugars is correlated with complications, there is a real concern that this early onset of diabetes will lead to an increased risk of early onset of complications.

• Women - Higher Prevalence, Risk of Complications of Pregnancy, and Future Risk for the Child

  Existing data on gestational diabetes (GDM) in Aboriginal peoples in Canada give cause for concern. A study by Harris et al in Sioux Lookout Zone found GDM rates of 8.4% - the highest rate reported so far in a Canadian population⁽³⁹⁾. In another study based in Sioux Lookout Zone, 70% of women with GDM went on to develop overt diabetes within three years⁽⁴⁰⁾. In the general population the typical conversion rate ranges between 25% and 60% over a decade or more⁽⁴¹⁾.

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