摘要：Objectives. We estimated the prevalence of overweight and obesity in Cree Canadian children aged 5 years (n=1044) using international and US growth references and examined the longitudinal tracking of weight categories between ages 2 and 5 years (n=562). Methods. Weight categories based on body mass index (calculated from measured heights and weights) were derived from the International Obesity Task Force (IOTF) and the Centers for Disease Control and Prevention (CDC) references. Results. According to the IOTF reference, 52.9% of children were overweight (31.6%) or obese (21.3%) whereas with the CDC reference, 64.9% were overweight (27.5%) or obese (37.4%). The IOTF and CDC references provided dissimilar tracking of weight categories. Based on the IOTF reference, 4.9% of the children who were normal weight at age 2 years were obese at age 5 years. Based on the CDC reference, 14.9% of children categorized as normal weight at age 2 years were obese at age 5 years. Conclusions. The IOTF reference provided more conservative estimates of obesity than the CDC reference, and longitudinal analyses showed dissimilar tracking of weight categories with the 2 references. Public health responses to obesity prevalence estimates should be made with awareness of methodological limitations. The prevalence of pediatric overweight and obesity in Canada has increased dramatically since the early 1980s, creating a public health concern. 1 ( Note. The terms overweight and obese are used to denote increased body mass index [BMI]. These terms are used by the International Obesity Task Force [IOTF] to identify increased BMI, but the Centers for Disease Control and Prevention [CDC] uses the terms at-risk of overweight and overweight . We appreciate the different terms used in these references; however, the terms overweight and obese are used in this manuscript for simplicity.) In Canada, childhood growth is not monitored with a national surveillance system, so prevalence estimates have been derived from local, 2 regional, 3 and national surveys. 4 Overweight and obesity prevalence data from Canadian children (aged approximately 6 to 12 years) and adolescents (aged approximately 13 to 17 years) have been well described, 4 – 7 but recent reports have also included preschool boys and girls (aged approximately 2 to 5 years). Data from preschool children collected during the Canadian National Longitudinal Survey of Children and Youth in the mid- to late 1990s indicated that many preschool children were overweight or obese. 8 Among children aged 2 to 3 years, approximately 18% were overweight (but not obese) and approximately 27% were obese. Among children aged 4 to 5 years, approximately 17% were overweight (but not obese) and approximately 23% were obese. 8 However, because heights and weights were parent-reported, the true prevalence level of obesity may have been underestimated owing to biased reporting. 9 Recent studies that used measured height and weight data showed that about 30% of children aged 2 to 6 years (n=1370) in 2 regions of Ontario were either overweight or obese, 10 and among children aged 3 to 5 years in Newfoundland and Labrador (n=4161), 16.8% of boys and 18.5% of girls were overweight while 7.8% of boys and 8.2% of girls were obese. 3 Results from the Canadian Community Health Survey, which were based on measured heights and weights obtained in 2004, indicated that 13% of children aged 2 to 5 years were overweight and 6% were obese. 11 In North America, Aboriginal peoples are the descendants of the original inhabitants of that continent. In Canada, the term “Aboriginal peoples” is inclusive of First Nations, Inuit, and Métis. In the United States, “American Indian” and “Native American” are the terms used to describe First Nations people. 12 Community-based surveys have indicated that First Nations children in Canada and American Indian children in the United States may be at particular risk for obesity. 13 In the Canadian Community Health Survey, 41% of Aboriginal children aged 2 to 17 years were overweight (21%) or obese (20%), which is a greater prevalence than that seen for other ethnic groups. 11 There is evidence from a few small community-based studies that overweight is prevalent in preschool First Nations children. In a published report based on measured heights and weights, 34.6% of First Nations boys (n = 78) and 45.2% of First Nations girls (n = 62) aged 2 to 5 years living in the remote Ontario community of Sandy Lake were overweight or obese. 14 In another study that used measured data, high BMI was common among First Nations children aged 4 to 19 years (n = 719) living in the Island Lake Tribal Council in Manitoba. In that study, 85% of girls aged younger than 8 years were overweight (25%) or obese (60%) and 80% of boys were overweight (28%) or obese (52%). 15 The issue of excess body weight in young children is very relevant in First Nations communities given their potentially increased risk for type 2 diabetes. 15 – 17 Given the public health concern of overweight and obesity in young children, there has been a call for early surveillance of childhood obesity in Canada and for longitudinal research to understand the pattern of excess weight gain. 18 There are, however, several issues concerning the definition and measurement of overweight and obesity that must be considered when surveillance and tracking are undertaken. For example, the term obesity refers to an excessive amount of adipose tissue in relation to lean body mass whereas overweight refers to excess weight in relation to height. Although the term overweight may imply a lesser degree of excess fat than is associated with obesity, no criteria exist to make this distinction. 19 From a classification perspective, prevalence estimates of overweight and obesity will vary as a function of the reference population used to group children into relative weight categories. 20 , 21 However, in a position paper developed by the Dietitians of Canada, Canadian Paediatric Society, College of Family Physicians of Canada, and Community Health Nurses Association of Canada, 22 it was recommended that the IOTF reference 23 be used when making population-based comparisons of BMI-based weight categories whereas the CDC growth charts for the United States 24 should be used in clinical and community settings for individual assessments of children. These recommendations were made on the basis of expert opinion, because empirical data were lacking. 25 The IOTF reference used age- and gender-specific BMI cutoffs created with data from 6 international surveys of children, and statistical procedures were used to align BMI cutoffs in childhood that corresponded to adult cutoffs for overweight (BMI≥ 25 kg/m2) and obesity (BMI≥ 30 kg/m2). In the IOTF classification system, children are designated as neither overweight nor obese , overweight , or obese . The CDC growth charts, in contrast, were derived from US data exclusively and use age- and gender-specific BMI cutoffs to categorize children along the BMI continuum as underweight (BMI<5th percentile), normal weight (BMI≥ 5th percentile and<85th percentile), at risk of overweight (BMI≥ 85th percentile and<95th percentile), or overweight (BMI≥ 95th percentile). Given that the IOTF and CDC references were developed from unique data sets and used different statistical methods and theoretical approaches, each method generates dissimilar estimates of overweight and obesity. 21 Furthermore, because different terms are used by the IOTF and CDC to describe children in different BMI weight categories, it is often difficult to make comparisons among studies. Few American Indian children were included in the development of the CDC reference, and none were included in the IOTF reference. Despite the inadequate representation of American Indian children, the CDC reference is used to classify them into weight categories. 13 It is noteworthy that no Canadian data (neither Aboriginal nor non-Aboriginal) were included in the development of the IOTF and CDC standards. Unfortunately, the current lack of nationally representative measured height and weight data from Canadian children precludes the development of Canadian growth charts, so the use of methods and standards developed by other countries is required to monitor childhood overweight and obesity in Canada. The Indian and Inuit Health Committee of the Canadian Paediatric Society supports the use of CDC growth charts to monitor child growth, while recognizing that First Nations and Inuit children may have growth patterns that differ from the reference population of children who were used to derive the CDC charts. 26 Presently, there is limited information regarding the magnitude of overweight and obesity in preschool-aged First Nations children in Canada. There is no information of the comparability of prevalence estimates obtained with the IOTF and CDC references in young children of First Nations descent and it is unknown whether these 2 methods provide comparable longitudinal tracking of relative weight categories in First Nations children. Therefore, our objectives were 2-fold: (1) to determine the prevalence of overweight and obesity in preschool First Nations boys and girls aged 5 years living in northern Quebec with both the IOTF and CDC references, and (2) to examine the longitudinal tracking of weight categories between ages 2 and 5 years with the IOTF and CDC references in First Nations boys and girls who had heights and weights measured at both ages.
