Chapter 4: Diabetes in Canada: Facts and figures from a public health perspective – Type 2 diabetes

Chapter 4 – Reducing the risk of type 2 diabetes and its complications

Introduction

Type 2 diabetes is caused by a combination of genetic, behavioural and environmental factors. Although no cure exists, there is growing evidence that type 2 diabetes and its complications can be prevented through the reduction of key risk factors. Currently, all the risk factors for type 1 diabetes are not well known, but researchers believe that interactions between genetic and environmental factors are involved (Chapter 5).^{Footnote 1}

Risk factors for type 2 diabetes can be classified as modifiable and non-modifiable. Modifiable risk factors are those that can be changed to reduce an individual's risk of developing type 2 diabetes and include unhealthy weight, physical inactivity, unhealthy eating, and smoking. Non-modifiable risk factors are individual characteristics, such as age, ethnicity, and family history of the disease. Research aimed at better understanding the multiple causes and their interactions continues. Understanding the distribution of risk factors within the population is useful for predicting future trends in type 2 diabetes incidence and prevalence, as well as trends in diabetes complications and mortality. It also provides information that can help in the planning of prevention interventions.

Key modifiable risk factors for type 2 diabetes

Overweight and obesity

Overweight, and particularly obesity, is the most important risk factor for type 2 diabetes and its complications. Excess body weight impairs the effectiveness of insulin use in the body, leading to increased demand on the pancreas to produce insulin. This demand cannot be met indefinitely and insulin production eventually declines, leading to type 2 diabetes. Overweight and obesity also increase an individual's risk of other chronic diseases, such as cardiovascular disease, arthritis, sleep and breathing disorders, depression, and some cancers.^{Footnote 2 Footnote 3}

When the energy consumed through foods is not balanced by energy expended through physical activity, unused calories are stored in the body as fat, which can accumulate in excess and results in overweight and obesity (Box 4-1). However, the causes of overweight and obesity are complex. Although unhealthy eating and physical inactivity contribute directly to weight gain, many factors influence these behaviours, including individual, environmental, societal, and cultural factors.

Box 4-1. Body mass index

Overweight and obesity by age

Among Canadians, the prevalence of self-reported obesity increases steadily through adulthood, peaking in individuals aged 60 to 69 years and declining thereafter (Figure 4-1). In 2009-2010, the prevalence of obesity in the 60 to 69 year age group was 22.5% for females and 22.6% for males. Overall, males were significantly more likely to be overweight or obese than females at every age. This difference was mostly due to the much higher proportion of males (40.6%) who self-reported being overweight compared to females (27.2%), as the proportion of males who self-reported being obese (19.5%) was comparatively similar to that of females (16.7%).

Figure 4-1. Prevalence† of self-reported overweight and obesity‡ among individuals aged 18 years and older, by age group and sex, Canada, 2009-2010

† 95% confidence intervals were based on a proportion that included both overweight and obesity.

‡ Overweight based on a BMI greater than or equal to 25.0 kg/m2 but less than 30.0 kg/m2; obesity based on a BMI greater than or equal to 30.0 kg/m2.

Source: Public Health Agency of Canada (2011); using 2009-2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-1]

Overweight and obesity by province/territory

The geographic distribution of individuals who are overweight or obese is similar to the geographic distribution of individuals with diagnosed diabetes (Chapter 1, Figure 1-2). In 2009-2010, the highest proportions of individuals with self-reported obesity were generally found in the Atlantic provinces, Saskatchewan, Manitoba, and the Northwest Territories (Figure 4-2).

Figure 4-2. Age-standardized^† prevalence of self-reported overweight and obesity^‡ among individuals aged 18 years and older, by province/territory, Canada, 2009–2010

† Age-standardized to the 1991 Canadian population.

‡ Overweight and obesity based on a BMI greater than or equal to 25.0 kg/m².

Source: Public Health Agency of Canada (2011); using 2009–2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-2]

Overweight and obesity over time

Over the last 30 years, there have been significant increases in the rates of overweight and obesity in the Canadian population, including children and youth. The proportion of adolescents aged 12 to 17 years shown to be obese by physical measurements tripled from 3% in 1978 to 9.4% in 2004.^{Footnote 4} Overweight and obesity in adolescence often persists into adulthood,^{Footnote 5 - Footnote 8} placing these individuals at risk of type 2 diabetes and other chronic diseases.^{Footnote 9 Footnote 10} This increase in obesity is likely contributing to the emergence of type 2 diabetes in youth, a disease that was previously viewed as an adult-onset disease only (Chapter 5, Type 2 diabetes).

Both measured and self-reported obesity among the Canadian population aged 18 years and older increased between 1978 and 2009-2010 (Figure 4-3). Based on self-reported weight and height, 18.1% of adults aged 18 years and older were obese in 2009-2010. However, self-reported measures are known to underestimate the true prevalence of obesity, which can only be obtained through physical measurements. In 2007-2009, based on measured height and weight, almost one in four (23.9%) Canadian adults aged 18 years and older was obese.

Figure 4-3. Prevalence of obesity^† (measured, self-reported, and estimated) among individuals aged 18 years and older^‡, Canada, 1978 to 2009-2010

† Based on a BMI greater than or equal to 30.0 kg/m².

‡ Data from the 1989 Canadian Heart Health Survey were based on respondents aged 18 to 74 years.

Source: Public Health Agency of Canada (2011); using measured data from the 1978/79 Canada Health Survey (Statistics Canada), 1989 Canadian Heart Health Survey (Statistics Canada), 2004 Canadian Community Health Survey - Nutrition (Statistics Canada), 2005 Canadian Community Health Survey (Statistics Canada), 2008 Canadian Community Health Survey (Statistics Canada), and 2007-2009 Canadian Health Measures Survey (Statistics Canada); using self-reported data from the 1985 and 1990 Health Promotion Survey (Statistics Canada), 1994/95, 1996/97 and 1998/99 National Population Health Survey (Statistics Canada); 2000/01, 2003, 2005, 2007, 2008, 2009-2010 Canadian Community Health Survey (Statistics Canada), and 2007-2009 Canadian Health Measures Survey (Statistics Canada).

[Click to enlarge Figure 4-3]

Diabetes and overweight/obesity

Figure 4-4 shows the distribution of BMI for Canadian adults with and without diabetes. The median BMI of 25 kg/m² for Canadians without diabetes indicates that half of all Canadian adults without diabetes are overweight or obese. The median BMI for Canadians with diabetes is four units (kg/m²) higher, at 29 kg/m². In this case, more than three quarters (75.6%) of Canadians with diabetes are classified as overweight or obese.

Figure 4-4. Distribution of self-reported body mass index (BMI)^† among individuals aged 18 years and older, by diabetes status, Canada, 2009-2010

† Marginal variance estimates for BMI greater than 40.0 kg/m2; data should be interpreted with caution.

Source: Public Health Agency of Canada (2011); using 2009-2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-4]

At every age, the prevalence of diabetes is higher among individuals who are overweight or obese (Figure 4-5). The association is more pronounced among females than males. Among males aged 18 years and older, the prevalence of diabetes among overweight or obese individuals is 2.6 times higher than those who are of normal weight (9.7% versus 3.8%), while among females aged 18 years and older the prevalence is nearly four times higher among overweight or obese individuals than among those with normal weight (9.6% versus 2.6%).

Figure 4-5. Rate ratios of self-reported diabetes among individuals aged 18 years and older who were overweight and obese versus normal weight† , by age group and sex‡, Canada, 2009-2010

† Based on a BMI cut-off of 25 kg/m².

‡ Marginal variance estimates for data in age groups less than 60-69 years; data should be interpreted with caution.

Source: Public Health Agency of Canada (2011); using 2009-2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-5]

Physical inactivity

Physical activity helps an individual maintain a healthy weight, strengthen the body, and reduce stress, as well as prevent chronic diseases (including type 2 diabetes), complications, and premature death.^{Footnote 11} Physical activity has also been shown to improve glycemic control, decrease insulin resistance, lower blood pressure, and improve blood lipid levels, regardless of body weight.^{Footnote 12 Footnote 13 Footnote 14}

To obtain health benefits, the Canadian Physical Activity Guidelines recommend that children and youth aged five to 17 years practice at least 60 minutes of physical activity (moderate to vigorous intensity) per day; adults should practice at least 150 minutes of aerobic physical activity (moderate to vigorous intensity) in total per week.^{Footnote 15} Physical activity recommendations for individuals with diabetes are presented in the Canadian Diabetes Association clinical practice guidelines.^{Footnote 16}

Given its importance for preventing and managing type 2 diabetes, understanding the barriers to physical activity among Canadians is essential to the development of interventions to encourage regular physical activity. The 2007 Physical Activity Monitor^{Footnote 17} identified the most frequently reported barriers to physical activity for adults in the general population as:

• Lack of time (72%);
• Lack of energy, or fatigue (64%);
• Lack of interest or motivation (62%);
• Long-term illness, injury or disability (60%);
• Cost (41%);
• Feeling ill at ease or uncomfortable (40%);
• Fear of injury (34%); and
• Lack of physical skill (34%).

The barriers to children's physical activity, as reported by parents, were different from those of adults. Safety concerns – such as too much traffic, poorly maintained sidewalks and bike lanes, and poor lighting – ranked highest while perception of a child's lack of skill for doing physical activity ranked lowest.

Physical inactivity by age

In 2009-2010, almost half (45.2%) of Canadians aged 12 years and older reported that they were inactive (leisure and transportation index)ⁱ. Although youth (aged 12 to 19 years) were more active than adults, almost a quarter (24.0%) were physically inactive. A higher proportion of females aged 12 to 19 (28.6%) than males aged 12 to 19 (19.4%) were physically inactive. Physical activity decreased with advancing age, and females were more inactive than males across all age groups (Figure 4-6).

Figure 4-6. Prevalence of self-reported physical inactivity^† among individuals aged 12 years and older, by age group and sex, Canada, 2009-2010

† Based on a leisure and transportation index measure.

Source: Public Health Agency of Canada (2011); using 2009-2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-6]

Physical inactivity by province/territory

The geographical distribution of physical inactivity was similar to that of obesity, with the proportion of the population reporting physical inactivity (leisure and transportation index) generally increasing from west to east and higher in the Northwest Territories and Nunavut (Figure 4-7).

Figure 4-7. Age-standardized^† prevalence of self-reported physical inactivity^‡ among individuals aged 12 years and older, by province/territory, Canada, 2009–2010

† Age-standardized to the 1991 Canadian population.

‡ Based on a leisure and transportation index measure.

Source: Public Health Agency of Canada (2011); using 2009–2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-7]

Unhealthy eating

Healthy weights depend on the balance of calories consumed with energy expended. Unhealthy food choices can increase the risk of diabetes, particularly when over-consumption results in overweight or obesity. Conversely, healthy eating can play an important role in the prevention of many chronic diseases. Consumption of vegetables and fruit, nuts, legumes, fish/seafood, whole grains, poultry, low-fat dairy products are all part of a healthy diet, as defined within Eating well with Canada's Food Guide.^{Footnote 18} Soluble fibre, found in foods such as citrus fruits, berries, legumes, oats, and brown rice, helps to regulate glycemia.^{Footnote 19} Foods that are rich in fibre can help to control weight and may reduce the risk of type 2 diabetes. Fibre also lowers total blood cholesterol and protects against heart disease.^{Footnote 20} Some evidence suggests that a lack of vitamin D hinders insulin function and glycemic control, and is a potential risk factor of type 1 and type 2 diabetes.^{Footnote 21 Footnote 22}

Negative food choices include excessive alcohol consumption and consumption of processed foods. A recent study implicates red meat as a risk factor for type 2 diabetes. After controlling for other lifestyle and dietary factors as well as age and BMI, daily consumption of unprocessed red meat increased risk of diabetes by 19%, while processed red meat increased risk by 51%.^{Footnote 23} Consumption of fat should be limited to less than 35% of total calories consumed.^{Footnote 24} Although daily fat intake represented 31% of caloric intake in 2004, Canadians still exceeded the upper limit for fat intake because overall caloric intake remained above recommended levels. The 31 to 50 year age group had the largest proportion of males (27%) and females (28%) who consumed excess fat. The main sources of fat for adults were from the "meat and alternatives" food group, followed by the "other foods" category, which included salad dressings, butter, margarine, and vegetable oils.^{Footnote 24} The combination of diabetes and hyperlipidemia can increase the risk of cardiovascular disease and kidney disease.

Many factors influence food choices and eating patterns among Canadians, including:

• Awareness of the connections between nutrition and health (nutritional knowledge);
• Perceptions of healthy eating based on current dietary guidance, importance given to freshness, unprocessed and homemade foods, and cultural/traditional meanings attached to foods and health;
• Exposure to media advertising or vendors promoting and selling individual products that tend to be high in energy and low in nutrients; and
• Lower socio-economic status and social inequity, which have been linked to poorer diet and nutritional status and have led to community initiatives such as food policy councils.^{Footnote 25}

Inadequate daily consumption of vegetables and fruit is used as a proxy measure of unhealthy diet. A criticism of this measure is its use of an outdated recommendation of at least five servings daily, which has now been increased to seven to eight servings daily. Further, the CCHS did not examine the quantity consumed, but only indicated the number of times vegetables or fruit are consumed. However, this indicator has been found to be an acceptable proxy for healthy eating habits due to its correlation to the Health eating index.^{Footnote 26} A diet that includes vegetables and fruit may help prevent obesity. Also, low frequency of vegetable and fruit consumption is associated with other lifestyle risk factors such as physical inactivity, tobacco smoking, and obesity.^{Footnote 27}

Unhealthy eating by age

Age-standardized rates of vegetable and fruit consumption indicated a marginal improvement over time. Between 2003 and 2010, 58.7% to 56.4% of Canadians did not eat enough vegetables and fruit. Males consistently consumed less vegetables and fruit compared to females.^{Footnote 28} More importantly, in 2009-2010, more than half of Canadians aged 12 years and older (55.9%) were still reporting eating less than the recommended five servings of vegetables and fruit a day. Compared to males, a greater proportion of females aged 12 years and older met the recommendations in every age group, but still almost half (49.5%) did not meet the recommendations. Almost two-thirds (62.6%) of males aged 12 years and older did not meet the recommendations (Figure 4-8).

Figure 4-8. Prevalence of self-reported inadequate vegetable and fruit consumption^†among individuals aged 12 years and older, by age group and sex, Canada, 2009-2010

† Based on a vegetable and fruit consumption of less than five times per day.

Source: Public Health Agency of Canada (2011); using 2009-2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-8]

Unhealthy eating by province/territory

Rates of inadequate vegetable and fruit consumption vary across the country with the highest rates in Newfoundland and Labrador, Nunavut, and the Northwest Territories. The scarcity of fresh vegetables and fruit and the dietary patterns of the Aboriginal population may explain lower consumption rates in the northern areas (Figure 4-9).

Figure 4-9. Age-standardized^† prevalence of self-reported inadequate vegetable and fruit consumption^‡ among individuals aged 12 years and older, by province/territory, Canada, 2009–2010

† Age-standardized to the 1991 Canadian population.

‡ Based on a vegetable and fruit consumption of less than five times per day.

Source: Public Health Agency of Canada (2011); using 2009–2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-9]

Tobacco smoking

Cigarette smoking can increase glycemic levels, impair insulin sensitivity, and promote abdominal obesity,^{Footnote 29} and has been associated with an increased risk of type 2 diabetes.^{Footnote 30 Footnote 31} The combination of diabetes and cigarette smoking can increase the risk of some of the most serious complications of diabetes: cardiovascular disease, kidney disease, and neuropathy.^{Footnote 32} Thus, smoking cessation is a key element of type 2 diabetes prevention and management.^{Footnote 16}

Tobacco smoking by province/territory

The Canadian Tobacco Use Monitoring Survey (CTUMS) is a Health Canada survey specific to the surveillance of tobacco smoking in Canada. Based on CTUMS data, in 2009, 13.6% of Canadians aged 15 years and older were daily tobacco smokers (12.1% of females; 15.1% of males). However, because CTUMS currently does not survey the territories, all subsequent statistics on tobacco smoking in this report are based on CCHS data.

Based on the CCHS, the proportion of individuals who smoked daily varied by province/territory. In 2009-2010, the lowest rates of smoking among individuals aged 18 years and older was reported in British Columbia, Ontario, and Manitoba. The rates of daily tobacco smoking were below 24% in all provinces, while in the territories the rates were all above 30% (Figure 4-10).

Figure 4-10. Age-standardized^† prevalence of self-reported daily tobacco smoking among individuals aged 18 years and older, by province/territory, Canada, 2009–2010

† Age-standardized to the 1991 Canadian population.

Source: Public Health Agency of Canada (2011); using 2009–2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-10]

Tobacco smoking over time

Rates of smoking have been declining in Canada, although the decline was more pronounced for females when compared to males (Figure 4-11). Based on age-standardized CCHS data, in 2010 15.5% of Canadians aged 12 years and older were daily tobacco smokers (13.0% of females; 18.1% of males).

Figure 4-11. Age-standardized^† prevalence of self-reported daily tobacco smoking among individuals aged 12 years and older, by sex, Canada, 2003 to 2010

† Age-standardized to the 1991 Canadian population.

Source: Public Health Agency of Canada (2011); using 2003, 2005, 2007, 2008, 2009, and 2010 data from the Canadian Community Health Survey (Statistics Canada).

[Click to enlarge Figure 4-11]

Populations at risk for type 2 diabetes

Individuals with pre-diabetes

Pre-diabetes is a state in which an individual's fasting glycemic levels and/or response to a fasting glucose tolerance test are higher than normal, but not high enough for a diagnosis of diabetes. Pre-diabetes is diagnosed if IFG, measured by a fasting plasma glucose (FPG) test, is between 6.1 mmol/L and 6.9 mmol/L or if IGT, measured by a oral glucose tolerance test (OGTT), is between 7.8 mmol/L and 11.0 mmol/L.^{Footnote 16} An individual may have pre-diabetes without knowing it because it is asymptomatic and can only be detected through specific blood tests.

Individuals with pre-diabetes are five to ten times more likely to progress to type 2 diabetes than those with normal glycemic levels,^{Footnote 33} and are also at an increased risk of cardiovascular disease. Only 3% to 5% of individuals with normal glycemic levels will typically develop type 2 diabetes over eight to ten years, whereas 30% of pre-diabetes cases with either IFG or IGT will develop the disease. For high-risk pre-diabetes cases involving both IFG and IGT, the conversion rate is 60% — 20 times higher than among individuals with normal glycemic levels.^{Footnote 34} These individuals can benefit most from early detection and intervention to prevent or delay the onset of type 2 diabetes and its complications.

It is estimated that pre-diabetes affects roughly 5.0 million Canadians over the age of 20 years. This number is expected to grow significantly over the next decade — to 6.3 million Canadians by 2016, according to some estimates.^{Footnote 35} Among those aged 40 to 74 years, the prevalence is expected to increase by 43.3%, from about 3.0 million in 2004 to 4.3 million in 2016. The forecast increases are largely due to the aging of the population, the growth in obesity, and the increase in non-white ethnicity.

Individuals with metabolic syndrome

Researchers have identified a set of conditions that often occur together and greatly increase the risk of type 2 diabetes and cardiovascular disease.^{Footnote 36} This constellation of risk factors is known as the metabolic syndrome (Box 4-2).

Box 4-2. Clinical criteria for the diagnosis of metabolic syndrome

The risk factors for metabolic syndrome — age, family history, overweight or obesity, unhealthy eating and physical inactivity — have been linked to both type 2 diabetes and cardiovascular disease. It is important for individuals to recognize symptoms early and to undertake lifestyle changes, including weight loss and physical activity, to reduce potential risks of both type 2 diabetes and cardiovascular disease. According to laboratory measures from the 2007-2009 CHMS, 15.2% of Canadians met the clinical criteria for metabolic syndromeⁱⁱ (Table 4-1).

Women with gestational diabetes

Several factors place females at increased risk of gestational diabetes: obesity, a history of gestational diabetes, a history of abnormal glycemic metabolism, a family history of diabetes, belonging to an ethnic group with a high prevalence of diabetes, and age (≥25 years).^{Footnote 37}

Females diagnosed with gestational diabetes are at an increased risk of pre-diabetes and type 2 diabetes in the first five to ten years following the birth of their baby.^{Footnote 38} Females with a history of gestational diabetes are advised to have a diabetes screening test (OGTT) within six months following delivery and to be routinely screened for type 2 diabetes thereafter;^{Footnote 16} however, the actual rate of postpartum diabetes screening is low.^{Footnote 40} Children of women with a history of gestational diabetes are also at an increased risk of obesity and type 2 diabetes.^{Footnote 41-44} Canadian Diabetes Association guidelines recommend that all pregnant women should be screened for gestational diabetes, and that females with multiple risk factors should be screened regularly during the pregnancy.16 Females who have had gestational diabetes can reduce their risk of type 2 diabetes through close postpartum monitoring and maintenance of a healthy lifestyle.^{Footnote 16}

Individuals with a mental illness

Depression and schizophrenia are two mental illnesses that are more common among individuals with diabetes than among those without diabetes.^{Footnote 45-49} Some studies have identified schizophrenia as a risk factor for type 2 diabetes.^{Footnote 16 Footnote 50-52} In 2005, 11.9 % of Canadians aged 18 years and older with schizophrenia reported having diabetes, compared to 5.3% of those without schizophrenia.^{Footnote 53}

A number of medications used to treat schizophrenia may affect glycemic levels and cause or exacerbate diabetes.^{Footnote 54} The use of second generation atypical antipsychotics increases the risk of diabetes in individuals with schizophrenia by 30% compared to those with diabetes on first generation antipsychotics.^{Footnote 55} Another large study also linked atypical antipsychotics with diabetes risk in individuals with schizophrenia, but found that risk differed by type of drug. Olanzapine and clozapine were implicated with the highest risk for diabetes, while aripiprazole, risperidone, quetiapine and ziprasidone were associated with the lowest risk.^{Footnote 56} The association between schizophrenia and diabetes is multi-factorial and may also be related to behavioural risk factors and living conditions. Individuals with schizophrenia have higher rates of tobacco smoking (and are more likely to be nicotine dependent), poor diet and physical inactivity.^{Footnote 54} Compared with individuals without schizophrenia, individuals living with the disease are also more likely to have a lower socioeconomic status and to complete less years of education, both of which are known to increase the risk of obesity.^{Footnote 48 Footnote 52 Footnote 57} Elevated hormone levels associated with schizophrenia are known to increase appetite, lead to weight gain, and cause insulin resistance.

Depression is common in Canada, with one in eight Canadians (12.2%) reporting symptoms consistent with depression at some point during their lifetime.^{Footnote 57} Depression can also contribute to type 2 diabetes, although it is still unclear what the causal relationship is between these two conditions and whether the relationship may in fact be bi-directional (Chapter 2, Mental illness).^{Footnote 58 Footnote 59} This may be an indirect relationship, as depression is associated with health behaviours, including smoking, physical inactivity, and unhealthy eating, that can increase the risk of type 2 diabetes. The side effects of medications and biological changes in the body have also put individuals with depression at an increased risk of type 2 diabetes.^{Footnote 46} For example, a study using Saskatchewan health administrative data reported that individuals with newly diagnosed depression treated concurrently with selective serotonin reuptake inhibitors and tricyclic antidepressants were at almost twice the risk of type 2 diabetesⁱⁱⁱ compared to those treated with tricyclic antidepressants alone.^{Footnote 60}

Key non-modifiable risk factors for type 2 diabetes

Ethnicity

Ethnicity has been associated with diabetes, where certain ethnic subpopulations in Canada have higher rates of type 2 diabetes. The influence of ethnicity reflects both biological and behavioural differences that influence diabetes risk. For instance, people of South Asian, Hispanic American, Chinese, and African ancestry are at higher risk of developing type 2 diabetes than those of European descent, and if they do develop type 2 diabetes, it is at an earlier age and with lower BMI values.^{Footnote 11 Footnote 61} Further, another incongruity was seen with BMI for non-Europeans, where BMI significantly underestimated the greater amount of visceral adipose tissue seen in this group.^{Footnote 62} Genome studies have also pointed to specific ethnic differences in genes that increase risk for type 2 diabetes.^{Footnote 63}

Ethnicity has also been associated with certain behavioural risk factors for type 2 diabetes. Compared to Caucasians, other race or ethnicities tended to have higher rates of physical inactivity, but individuals of Filipino, Chinese, or South Asian descent were between 1.6 to 6.0 times less likely to be obese (Table 4-2). Inadequate consumption of vegetables and fruit was higher among individuals of Chinese and Filipino descent compared to Caucasians, but was generally high in all ethnicities (ranging from 56.0% to 65.5%). Caucasians tended to smoke more than the other groups. Also, self-care behaviour such as home glucose testing or foot examinations, may vary by ethnicity, which could impact the quality of life of those living with diabetes.^{Footnote 64}

Immigration

Immigrants to Canada, most of who now originate from non-European countries, are known to have higher rates of diabetes. Results from an Ontario population-based study showed that, after controlling for age, immigration category, education, income and time since arrival, immigrants from South Asia, Latin America and the Caribbean, and sub-Saharan Africa had an increased risk of diabetes compared to immigrants from Western Europe and North America.^{Footnote 65} In addition to genetic susceptibility, there is evidence that recent immigrants tend to have lower incomes and poorer access to health services than the general Canadian population.^{Footnote 66} While the evidence on this topic remains mixed,^{Footnote 67 Footnote 68} a Toronto study identified high rates of diabetes with these factors, linking them by way of "high risk" built environments that included decreased access to walking and cycling trails, parks, and recreation programs and poorer access to healthy food choices or health education programs.^{Footnote 69} This may make these populations more vulnerable to risk factors for type 2 diabetes. On the other hand, immigrants who have lived in Canada for over 15 years present higher proportions of type 2 diabetes than recent immigrants, implying a "negative acculturation effect".^{Footnote 70}

Social and environmental factors influencing overweight and obesity

The determinants of health

The maintenance of a healthy body weight, participation in physical activity, and healthy eating are the primary goals of public health interventions aimed at preventing type 2 diabetes. However, an individual's health and the ability to adopt such healthy behaviours are influenced by many factors, including the social, environmental, cultural, and economic conditions in which the individual lives (the "determinants of health"). These include income, education and literacy; employment and working conditions; food security; environment and housing; early childhood development; social support and connectedness; and access to health care. All have a significant effect on the distribution of risk factors within a population and are, in effect, "the causes of the causes."^{Footnote 72} Consequently, to deal with individual health behaviours and choices, it is necessary to consider the factors that shape them.^{Footnote 73}

Socio-demographic factors

Low socio-economic status (as gauged by level of income, education, and employment status), rural residence and ethnicity have been found to be associated with diabetes, its complications, and its risk factors. In 2009-2010, several type 2 diabetes risk factors, including physical inactivity (leisure and transportation index), inadequate consumption of vegetables and fruit, and daily smoking were more common among Canadians in the lowest income quintile than among those in the highest income quintile (Table 4-3). Individuals with less education were also more likely to have risk factors for type 2 diabetes than those with higher education (Table 4-4). The association was less pronounced between urban-rural residence and the various risk factors (Table 4-5).

The built environment

Although individual and interpersonal factors such as attitudes and motivation may account in part for levels of physical activity, physical activity is also directly affected by a number of aspects of the built environment, such as urban sprawl^{Footnote 74} and access to walking paths, trails and sidewalks.^{Footnote 75} Built environments that promote high-energy diets, decreased access to healthy food stores, and sedentary lifestyles are known as obesogenic environments. In Canada, higher rates of obesity have been found in rural populations than in urban populations.^{Footnote 76 Footnote 77} This may in part be due to the reliance on vehicles for transportation to destinations because of the lack of convenient destinations within walking distance. In contrast, supportive built environments can play a facilitating role in encouraging physical activity.^{Footnote 78} For example, communities with a variety of destinations safely accessible by foot are associated with a higher prevalence of walking to work.^{Footnote 79} Research has also shown that individuals who can easily walk from home to commercial areas have increased levels of physical activity and lower BMI.^{Footnote 80}

The built environment also plays a role in healthy eating, alongside health and social policies that influence food marketing. Access to local shops, health-related stores, and supermarkets^{Footnote 81} has been associated with lower levels of obesity, while the reversed association has been observed between access to fast food restaurants and obesity.^{Footnote 82} The availability and accessibility of affordable nutritious foods is a particular challenge in low-income communities and in remote or northern communities, especially those inhabited primarily by Aboriginal populations, where dietary choice is constrained by high transport costs and spoilage.^{Footnote 25 Footnote 83}

Interventions for the prevention of type 2 diabetes

Interventions to prevent type 2 diabetes can focus on the individual or on the population as a whole. A population approach examines and addresses the entire range of factors that affect health and aims to reduce risk factors in the population as a whole. In contrast, the individual approach focuses on identifying risk factors and promoting behavioural change. Interventions can include programs that promote healthy eating, regular physical activity and the loss of excess body weight. While not as effective as lifestyle changes for longer term prevention, some medications can be taken in addition to lifestyle changes to manage pre-diabetes. Individual and population approaches are complementary and are most effective when they are integrated.

Primary prevention at the individual and population level is critical. Reducing the prevalence of obesity would reduce the risks of developing diabetes as well as many other chronic diseases. Therefore, the population approach to reducing diabetes focuses on creating supportive environments and communities that enable their residents to maintain an active lifestyle and healthy eating habits. It requires collaboration across sectors (such as the food, recreation and school sectors), multiple strategies coordinated at different levels, and sustained effort over time. Examples of health promotion strategies include:

• Increasing time for physical activity in the school curriculum;
• Providing access to community recreational facilities;
• Forming and supporting networks of community-based organizations and services committed to improving nutrition or physical activity;
• Instituting educational campaigns that enable people to read and understand food labels;
• Teaching young people to cook nutritious, low-fat foods;
• Providing training to staff and volunteers for the skills required to promote population health; and
• Mandating a local health service, such as a diabetes education centre, to work with local community groups to promote walking clubs.^{Footnote 84}

Prevention and health promotion strategies should be tailored to the level of health literacy of the target population in order to better address its needs. Health literacy is a person's ability to find, understand and use written information to promote, maintain and improve their health and is only partially attributed to education level. It differs from the basic ability to read or understand numbers in that it involves other complex skills, such as keeping up with constantly changing information on new diseases and health threats, identifying and resolving contradictory information from various sources, and communicating with doctors, friends, and family about diagnoses and treatment options.

Recognizing differing levels of health literacy in the population plays a role in understanding how healthy attitudes are shaped and, in the context of prevention and health promotion, how knowledge about diet, physical activity and other healthy behaviours can be shared. For example, 60% of Canadian adults do not have the literacy skills needed to adequately manage their health or health-care needs. Seniors, immigrants and the unemployed generally have lower levels of health literacy than the national average. Moreover, a link has been observed between health literacy and diabetes, where health regions with higher than average health literacy scores had lower rates of diabetes.^{Footnote 85}

Looking ahead

The causes of type 2 diabetes are multiple, interlinked, and complex. Therefore, a holistic approach that addresses the social, economic, environmental, genetic and lifestyle factors associated with type 2 diabetes is needed to prevent and mitigate the disease and its complications. Overweight and obesity rates have been increasing over time; reversing the course of this trend and addressing other modifiable risk factors will be a crucial step in limiting the rise of diabetes (Chapter 1). Efforts to prevent and manage diabetes and its complications will not only benefit affected or at-risk individuals and their families, but also the overall Canadian economy by reducing the economic burden of this disease (Chapter 3, Economic costs of diabetes).

The Government of Canada promotes the prevention and control of diabetes through a number of initiatives. The Canadian Diabetes Strategy (CDS), a component of the federal government's Integrated Strategy on Healthy Living and Chronic Disease, supports both the upstream prevention of type 2 diabetes through healthy eating and physical activity, as well as the targeted prevention of type 2 diabetes and its complications in high risk populations through early detection and self-management. The Aboriginal Diabetes Initiative (ADI), renewed for five years in 2010, supports the prevention and management of diabetes in First Nations and Inuit communities, both on- and off-reserve (Chapter 6, The Aboriginal Diabetes Initiative). Both the CDS and ADI support organizations that work with communities at high risk of developing type 2 diabetes and its complications by providing funding for the development and implementation of diabetes prevention, early detection, and self-management programs to address the unique needs of the populations they serve.

1. This measure likely underestimates true daily energy expenditure since it does not capture energy expended in usual daily activities, including work activities.
2. This analysis did not include drug treatments for elevated triglycerides, HDL, blood pressure, and plasma glucose as alternate indicators for metabolic syndrome risk factors; thus, it likely underreports the true prevalence of metabolic syndrome.
3. Adjusted odds ratio: 1.89; 95% CI: 1.35-2.65.