Chapter 1: Diabetes in Canada: Facts and figures from a public health perspective – Burden

Chapter 1 – The burden of diabetes in Canada

Introduction

Diabetes is a serious chronic disease that is on the rise in Canada. It poses a challenge not only to those living with the disease but also to their families, communities and the health care system.

Diabetes prevalence

Diabetes is one of the most common chronic diseases in Canada. In 2008/09, close to 2.4 million Canadians aged one year and older were living with diagnosed diabetes (either type 1 or type 2), according to the CCDSS (Table 1-1). This represented approximately 6.8% of the population, or 6.4% of all females aged one year and older and 7.2% of all males aged one year and older. When looking only at the adult population aged 20 and older, the prevalence rate was 8.7% (95% CI: 8.72-8.74%), representing one in 11 Canadians.

Prevalence by age

The proportion of people with diagnosed diabetes generally increases with age (Figure 1-1). The body's ability to produce and use insulin deteriorates as one ages, placing older adults at an elevated risk of developing type 2 diabetes. The sharpest increase in the prevalence of diabetes occurred after the age of 40 years. In 2008/09, the 75 to 79 year age group had the highest proportion of people with diagnosed diabetes (23.1% of females and 28.5% of males). Although diagnosed diabetes is more common in older age groups, more than 50% of the affected Canadian population (1.2 million) was of working age, between 25 and 64 years (Table 1-1).

Figure 1-1. Prevalence of diagnosed diabetes among individuals aged one year and older, by age group and sex, Canada, 2008/09

Source: Public Health Agency of Canada (July 2011); using 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-1]

Prevalence by province/territory

The prevalence of diabetes varies across Canada. In 2008/09, after accounting for differences in age distribution among the provinces and territories, Newfoundland and Labrador, Nova Scotia, and Ontario had the highest prevalence of diagnosed diabetes, while Nunavut, Alberta, and Quebec ranked lowest (Figure 1-2).

Figure 1-2. Age-standardized^† prevalence of diagnosed diabetes among individuals aged one year and older, by province/territory, Canada, 2008/09

† Age-standardized to the 1991 Canadian population.

Source: Public Health Agency of Canada (Septermber 2011); using 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-2]

Prevalence over time

The age-standardized prevalence of diagnosed diabetes among Canadians aged one year and older increased by 70%, from 3.3% in 1998/99 to 5.6% in 2008/09 (Figure 1-3). Prevalence over time was consistently higher among males than among females (Figure 1-3) and increased in every age group (Figure 1-4).

Figure 1-3. Age-standardized† prevalence and number of cases of diagnosed diabetes among individuals aged one year and older, Canada, 1998/99 to 2008/09

† Age-standardized to the 1991 Canadian population.

Source: Public Health Agency of Canada (July 2011); using 1998/99 to 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-3]

The aging of the Canadian population, largely a result of the baby boom cohort, has been one of the factors contributing to the increase in the number of Canadians living with diagnosed diabetes. In recent years, the highest increase in the number of individuals with diabetes was seen in the 60 to 64 year age group, from 127,608 individuals in 1998/99 to 313,521 individuals in 2008/09.^{Footnote 1}  In addition to the aging baby boom cohort, the increased longevity of individuals living with diabetes (due to advancements in treatment and earlier diagnosis) has contributed to the increasing prevalence rates of the disease.

Figure 1-4. Prevalence of diagnosed diabetes among individuals aged one year and older, by age group, Canada, 1998/99 to 2008/09

Source: Public Health Agency of Canada (July 2011); using 1998/99 to 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-4]

Although the actual number of Canadians with diagnosed diabetes has increased most rapidly in the older age groups, the proportion of individuals with diagnosed diabetes has increased more in younger age groups. Between 1998/99 and 2008/09, the greatest relative increases in prevalence was seen in the 35 to 39 and 40 to 44 year age groups, where the proportions doubled. The increase seen in younger age groups is likely mainly due to increasing rates of overweight and obesity (Chapter 4, Overweight and obesity).

Undiagnosed diabetes

Undiagnosed diabetes denotes cases of diabetes which have yet to be identified by a health care professional. Using fasting blood samples collected in the 2007-2009 Canadian Health Measures Survey (CHMS), the magnitude of undiagnosed diabetes in Canada was estimated using Canadian Diabetes Association definitions and guidelines (Box I-2).^{Footnote 2}  However, this analysis was limited due to the unavailability of a two hour oral glucose tolerance test and by a relatively small sample size. Based on plasma glucose readings, undiagnosed diabetes was found in 0.9% (95% CI: 0.5-1.4%) of the Canadian population aged six years and older, which represents more than 20% of all cases of diabetes (0.9% of the 4.3% cases detected in this analysis).

Diabetes incidence

Over 200,000 Canadians (6.3 new cases per 1,000 individuals) were diagnosed with diabetes for the first time in 2008/09 (Table 1-2). Males (6.8 new cases per 1,000 individuals) had higher overall incidence rates than females (5.7 new cases per 1,000 individuals).

Incidence by age

The incidence rates of diabetes rose steeply after age 40 among both sexes, peaking in the 70 to 74 and 75 to 79 year age groups (Table 1-2, Figure 1-5). Almost half of incident cases of diabetes in 2008/09 were aged between 45 to 64 years old. According to CCHS survey data based on the same age group, among those who self-reported having diabetes, 83.3% were of unhealthy weight (including 47.5% obese) compared to 57.8% with unhealthy weight (including 19.1% obese) among those without diabetes. This suggests that obesity was a major contributor to diabetes in that age group.

Figure 1-5. Incidence rates of diagnosed diabetes among individuals aged one year and older, by age group and sex, Canada, 2008/09

Source: Public Health Agency of Canada (July 2011); using 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-5]

Incidence by province/territory

Different trends in incidence over time were seen when data were stratified by province/territory (Figure 1-6). Although the overall Canadian trend showed a slight increase over time, this was largely influenced by increasing trends in Ontario, British Columbia, Saskatchewan, and the Northwest Territories. Generally declining or no significant trends over time were seen in the remaining provinces. However, these data may be unstable over time (with large confidence intervals) due to small populations. Factors that may influence incidence trends in each province/territory include changes in coding, diagnostic changes, incentive programs, or screening effects due to localized campaigns. For example, the Canadian Diabetes Association recommendation for type 2 diabetes screening has changed over time. In 1998, screening was recommended every three years for Canadians aged 45 years and older,^{Footnote 3}  while since 2003 the age was lowered to 40.^{Footnote 4}  This may increase the number of diabetes diagnoses.

Figure 1-6. Age-standardized^† incidence rates of diagnosed diabetes among individuals aged one year and older, by province/territory, Canada^‡, 1998/99 to 2008/09

^† Age-standardized to the 1991 Canadian population.

‡ Excluding Yukon and Nunavut.

Source: Public Health Agency of Canada (September 2011); using 1998/99 to 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-6a]

[Click to enlarge Figure 1-6b]

Incidence over time

Between 1998/99 to 2008/09, statistical analyses indicate an overall increase in incidence rates of diagnosed diabetes (Figure 1-7). However, only certain age groups contributed to this overall increase over time, namely children age one to 19 years and working-age adults aged 30 to 49 years old.^{Footnote 1}  Diabetes incidence appears to be decreasing since 2006/07, but it is too early to consider the implications of this small decrease at this point. Variations in incidence rates may be related to many data artefacts.

Figure 1-7. Age-standardized^† incidence rates and number of incident cases of diagnosed diabetes among individuals aged one year and older, Canada, 1998/99 to 2008/09

† Age-standardized to the 1991 Canadian population.

Source: Public Health Agency of Canada (July 2011), using 1998/99 to 2008/09 data from the Canadian Chronic Disease Surveillance System (Public Health Agency of Canada).

[Click to enlarge Figure 1-7]

Between 1998/99 and 2008/09, the age-standardized prevalence rate for diabetes increased by 72% for females and 69% for males, while the age-standardized incidence rate remained relatively comparable for both sexes. The increasing number of individuals being diagnosed with diabetes (incidence) does not entirely account for the increase in the total number of Canadians living with the disease (prevalence), indicating that people are living longer with diabetes, or that they are being diagnosed at a younger age.

Diabetes in the world

The seriousness of diabetes has been acknowledged at the global level. In one of its resolutions, the United Nations General Assembly recognized that: "[d]iabetes is a chronic, debilitating and costly disease associated with severe complications, which poses severe risks for families, Member States and the entire world […]".^{Footnote 5}  However, providing accurate estimates of the global burden of diabetes, in terms of morbidity and mortality, poses several challenges including the lack of valid and timely data in some countries, as well as the variability of diagnostic criteria used across the globe.

Keeping in mind these limitations, the International Diabetes Federation estimated that the global age-standardized prevalence of diabetes among adults aged 20 to 79 years was 6.4% in 2010, representing 285 million people worldwide.^{Footnote 6} ,^{Footnote 7}  Compared with the prevalence of diabetes in European, American and Oceania countries included in this study (Figure 1-8), the rate for Canada was the third highest. Compared to the rate of 9.2% in Canada, rates were much lower in all African countries, as well as in most Asian and Latin American/Caribbean countries. On average, countries in the Middle-East Crescent had higher rates than those seen in Europe, North America, and Oceania countries.

Figure 1-8. Prevalence^† of diabetes among individuals aged 20 to 79 years, Europe, North America and Oceania, 2010

† Standardized to the global population.

Source: Public Health Agency of Canada (2011); adapted from Shaw JE, Sicree RA, Zimmet PZ. Global estimates of the prevalence of diabetes for 2010 and 2030. Diab Res Clin Pract 2010;87:4-14.

[Click to enlarge Figure 1-8]

According to a report from the World Health Organization (WHO), in 2008, the global age-standardized prevalence of diabetes was 10%, and 1.3 million deaths were attributed to the disease. The prevalence of diabetes for both sexes was the highest in the Region of the Americas (11%), equally ranked with the Eastern Mediterranean Region, and lowest in the WHO European and Western Pacific Regions (at 9%).^{Footnote 8}

Looking ahead

If incidence and mortality rates remain at the levels seen in 2008/09^{Footnote i} , the number of Canadians aged one year and older living with diagnosed diabetes will reach 3.7 million (1.7 million females and 1.9 million males) by 2018/19, representing an increase of 56%. If current incidence and mortality trends continue^{Footnote ii}  , the projected number would be higher, at 3.8 million Canadians. The forecasted increase in the number of individuals diagnosed with diabetes in Canada poses a major challenge for health services; major disease prevention efforts should be made to avoid this anticipated rise.

It should be noted that reported prevalence rates for diabetes vary by data source used because of various differences in methodologies. For example, based on results from the 2009-2010 CCHS, the prevalence of self-reported diabetes was 6.8% (95% CI: 6.6-7.1%) among Canadians aged 20 years and older. In comparison, using the same age group (20 years and older), 2008/09 CCDSS data indicate a prevalence of diagnosed diabetes of 8.7% (95% CI: 8.72–8.74%).^{Footnote 1}  Both sources may in fact slightly underestimate the true prevalence of diabetes in Canada as undiagnosed cases of diabetes (up to 20% based on CHMS data) are not taken into account. More data and research are necessary to determine the magnitude of undiagnosed diabetes cases in Canada.

Although each data source has its strengths and limitations, this first chapter focused mainly on CCDSS estimates as it is the only national population-based data source, and it uses a validated case definition of diabetes. Unlike the CCHS, the CCDSS also allows for the estimation of incidence rates. The Public Health Agency of Canada is collaborating with the provinces and territories, as well other external partners, to improve on an ongoing basis the quality, validity, and comprehensiveness of CCDSS data.