This section provides an overview of population-level impacts of obesity, with a focus on health impacts (morbidity), mortality and economic implications.
Obesity is associated with a number of health conditions or morbidities.47,88 A recent systematic review of the clinical literature found associations between obesity and the incidence of type 2 diabetes, asthma, gallbladder disease, osteoarthritis, chronic back pain, several types of cancers (colorectal, kidney, breast, endometrial, ovarian and pancreatic cancers) and major types of cardiovascular disease (hypertension, stroke, congestive heart failure and coronary artery disease).89 There may also be a relation between psychiatric conditions and excess weight, although this may be confounded by the fact that some psychotropic medications can contribute to weight gain.90
Evidence from systematic reviews indicates that childhood obesity increases the risk of obesity during later life91 and contributes to the early development of a number of conditions, such as type 2 diabetes, atherosclerotic heart disease and high blood pressure.21,92
In adults, abdominal obesity is associated with an increased risk of type 2 diabetes and cardiovascular disease,93,94 and is the most prevalent feature of a set of metabolic disorders known as the metabolic syndrome*.94 In the 2007-2009 CHMS, 21% of men aged 20 to 39 years, 38% of those 40 to 59 and 52% of those 50 to 69 had a waist circumference indicating a higher health risk. The prevalence was even higher among women: 31% of those aged 20 to 39, 47% of those 40 to 59 and 65% aged 60 to 69.2 Among youth aged 15 to 19 years, 15% of males and 28% of females had a waist circumference indicating increased or high risk.24
Abdominal obesity has been studied in several Aboriginal populations because of its relation with diabetes and/or metabolic syndome.39-41,95-106 In the Believing We Can Reduce the Aboriginal Incidence of Diabetes (BRAID) study in rural northern Alberta, for example, approximately one-half of on-reserve First Nations adults met the criteria for metabolic syndrome, and abdominal obesity was the most prevalent abnormality.100
Analyses from the RHS also found associations between weight category and the prevalence of a number of health conditions, including cardiovascular disease, musculoskeletal disorders and respiratory diseases, in on-reserve First Nations communities. For example, the prevalence of self-reported cardiovascular disease increased by weight category: 8.3% of those of normal weight, 15.7% of the overweight, 26.5% of the obese and 44.6% of the severely obese.28
As noted in the Canadian clinical practice guidelines on obesity and elsewhere, complications of obesity include not only physical health problems but also psychological concerns (e.g., low self-esteem).22,107-109 As well, negative attitudes and stereotypes about those who are obese have been linked to social and employment discrimination.88 One systematic review reported perceptions of weight bias and negative stereotypes about obese people in a number of sectors: at work, in health care settings, in schools and in the media.110 An analysis of the 2002/03 CCHS results found that, compared with men and women of normal weight, obese men and women were more likely to report high job strain and low co-worker support.111
While severe obesity is associated with premature mortality, calculating the exact number of deaths in a population that are attributable to obesity is difficult. The relative risk of death varies among studies, depending on the population characteristics (e.g., age) and risk factors included in the analyses.112 Further complicating the issue are the methodological challenges of isolating the contribution of excess body weight from that of related risk factors, co-morbidities and confounding variables.113
What does the current research say about how many deaths in Canada can be attributed to obesity? One Canadian study estimated that the proportion of all deaths among adults 20-64 years of age that could be theoretically attributed to overweight and obesity grew from 5.1% in 1985 to 9.3% in 2000.114 Another study, involving 11,326 participants in the 1994/95 National Population Health Survey (NPHS) who were followed for 12 years, found that, compared with those in the normal weight category, those in the underweight or class II or III obesity categories had a significantly increased risk of all-cause mortality, even after key sociodemographic factors and health behaviours had been controlled for. In contrast, people who were overweight but not obese had a significantly lower risk than the normal-weight population. There was no significant difference in risk of mortality between obesity class I and normal-weight respondents.115
This pattern, in which mortality is higher in the highest and lowest weight categories compared with those who are of normal weight, has been described as a J- or U-shaped mortality curve.116,117 A similar J- or U-shaped relation between BMI and mortality has been reported in a number of US studies.118,119,120 The reasons for this pattern are unclear, and the phenomenon may be influenced by body composition. A national longitudinal survey in the US (NHANES I and II) found that, among men, fat mass (i.e., adiposity) had a positive relation with all-cause mortality, and fat-free mass had a negative or protective effect.121
An analysis of CCHS, NPHS and Economic Burden of Illness in Canada data (see Appendix 2) was conducted to examine the change in the economic burden of obesity between 2000 and 2008, taking into account the impact of inflation on health care costs and average earnings over the period. In this study, the economic burden of obesity was defined as both the direct costs to the health care system (i.e., hospital care, pharmaceuticals, physician care and institutional care) and indirect costs to productivity (i.e., the value of economic output lost as a result of premature death and short- and long-term disability). The study focused on eight chronic diseases consistently associated with obesity. According to this analysis, between 2000 and 2008 the annual economic burden of obesity in Canada increased by $735 million, from $3.9 to $4.6 billion (Figure 15).
Source: I. Janssen, unpublished manuscript for the Public Health Agency of Canada; based on analysis of the1994/95 and 1996/97 National Population Health Surveys; 2000/01, 2003, 2004, 2005, 2007 and 2008 Canadian Community Health Surveys (Statistics Canada); and Economic Burden of Illness 2000 Database (Public Health Agency of Canada).
Another study, using a comparable methodology and looking at 18 obesity-related chronic diseases, estimated the economic burden of obesity to be as high as $7.1 billion (2006 dollars).122
A study of physician costs in Ontario found that obese male and female adults (aged 18 and over) incurred physician costs that were 14.7% and 18.2% greater than those of normal-weight peers. The effect of obesity on physician costs increased with age: compared with normal weight groups, costs were 5.3% higher for obese young adults (18-39 years), 7.0% higher for obese middle-aged adults (40-59 years) and 28.3% higher for obese older adults (60+ years).123
* Metabolic syndrome is a cluster of metabolic abnormalities that is associated with an increased risk of type 2 diabetes and cardiovascular disease. Screening variables used to identify metabolic syndrome are abdominal obesity, low high-density lipoprotein cholesterol and elevated readings for triglycerides, blood pressure and fasting blood glucose.