Margot Shields

Canadian childhood obesity estimates based on WHO, IOTF and CDC cut-points

OBJECTIVE This article compares prevalence estimates of excess weight among Canadian children and youth according to three sets of body mass index (BMI) reference cut-points. The cut-points are based on growth curves generated by the World Health Organization (WHO), the International Obesity Task Force (IOTF), and the US Centers for Disease Control (CDC). A secondary objective is to compare estimates by method of data collection. METHODS Prevalence estimates of overweight and obesity were produced for 2- to 17-year-olds using the three sets of BMI cut-points. Estimates are based on data from 8 661 respondents from the 2004 Canadian Community Health Survey and 1 840 respondents from the 1978/79 Canada Health Survey. In both surveys, the height and weight of children were measured. RESULTS The 2004 prevalence estimate for the combined overweight/obese category is higher (35%) when based on the WHO cut-points compared with the IOTF (26%) or CDC (28%) cut-points. Estimates of the prevalence of obesity are similar based on WHO and CDC cut-points (13%), but lower when based on IOTF cut-points (8%). Absolute differences in excess weight estimates between 1978/79 and 2004 are similar based on the three sets of cut-points, but the relative increase is greater when based on the IOTF cut-points. Estimates vary substantially by method of data collection. CONCLUSION When interpreting prevalence estimates of overweight and obesity for children and youth, it is important to consider the definitions used and the method of data collection.

Dyslipidemia prevalence, treatment, control, and awareness in the Canadian Health Measures Survey.

BackgroundThe most recent Canadian population-level data on lipid levels are from 1992. This study presents current estimates of Canadians with dyslipidemia, the proportion aware of their condition, and the proportion being treated and below target values.MethodsThe Canadian Health Measures Survey (2007–2009) assessed the prevalence, awareness and treatment of dyslipidemia. Dyslipidemia was defined as TC/HDL-C ratio ≥5; measured LDL-C ≥3.5 mmol/L; or taking lipid-modifying medications. The 2009 guidelines for the diagnosis and treatment of dyslipidemia were used to define low, moderate or high cardiovascular disease (CVD) risk and treatment initiation and targets.ResultsForty-five percent of Canadians aged 18–79 years have dyslipidemia. Fifty-seven percent of respondents were not aware of their condition. Lipid-modifying therapy was initiated in individuals where treatment would be recommended in 49%, 20% and 54% of those at high, moderate, and low risk levels, respectively. The majority (81%) of those taking medication had their lipid levels under desirable levels, however, only 24% of those with dyslipidemia reported medication use. Overall, only 19% of those with dyslipidemia had their lipids under recommended levels. Only 41% of those taking lipid-modifying medication reached a recommended target of LDL-C <2 mmol/L or ApoB <0.8 g/L.ConclusionThere is still a high proportion of Canadians at high risk of CVD, with dyslipidemia, who are not being treated to recommended levels. These data need to be integrated into CVD reduction recommendations and represent an important baseline for assessing progress.RésuméContexteLes plus récentes données en population sur les niveaux de lipides au Canada datent de 1992. Notre étude présente les estimations actuelles sur les Canadiens ayant une dyslipidémie, la proportion de gens connaissant leur état et la proportion traitée pour une dyslipidémie, mais présentant des valeurs sous-optimales.MéthodeL’Enquête canadienne sur les mesures de la santé (2007–2009) a évalué la prévalence, la connaissance et le traitement des dyslipidémies. Une dyslipidémie était définie ainsi: ratio CT/HDLc ≥ 5; LDLc mesuré ≥ 3,5 mmol/L; ou prise de médicaments hypolipémiants. Nous avons utilisé les directives de 2009 pour le diagnostic et le traitement des dyslipidémies pour définir le risque de maladie cardiovasculaire (MCV) - faible, modéré ou élevé - ainsi que l’instauration du traitement et les valeurs cibles du traitement.RésultatsQuarante-cinq p. cent des Canadiens de 18 à 79 ans ont une dyslipidémie. Cinquante-sept p. cent des répondants n’étaient pas conscients de leur état. Des traitements hypolipémiants avaient été instaurés, dans les cas où ces traitements étaient recommandés, chez 49 %, 20 % et 54 % respectivement des sujets présentant un niveau de risque élevé, modéré et faible. La majorité (81 %) des sujets prenant des médicaments avaient des niveaux de lipides sous-optimaux, mais seulement 24 % des sujets ayant une dyslipidémie disaient prendre des médicaments. Globalement, seulement 19 % des sujets ayant une dyslipidémie avaient des niveaux de lipides sous les niveaux recommandés. Seulement 41 % des sujets prenant des hypolipémiants atteignaient la cible recommandée (LDLc <2 mmol/L ou Apo B <0,8 g/L).ConclusionIl y a encore une proportion élevée de Canadiens présentant un risque élevé de MCV, avec dyslipidémie, qui ne sont pas traités selon les niveaux recommandés. Ces données devraient être intégrées dans les recommandations sur la réduction des MCV; elles représentent aussi une importante base de référence pour évaluer les progrès.

Trends in aerobic fitness among Canadians, 1981 to 2007-2009.

Public health surveillance systems often monitor physical activity trends, but fitness assessment is relatively rare. This study investigated secular changes in aerobic fitness among Canadian adults and children. Participants aged 8-69 years were from 2 nationally representative surveys, conducted in-home in 1981 and in mobile examination centers in 2007-2009. In both surveys, submaximal step tests using progressive age- and sex-specific exercise stages were completed after initial screening (Physical Activity Readiness Questionnaire, heart rate, blood pressure). Between surveys, the step-test protocol had been modified to reduce underestimation of fitness among fitter and older individuals. Maximal oxygen uptake was estimated for adults using validated historical and updated prediction equations, adjusted to reflect protocol differences. Because these equations are not validated for young people, maximal aerobic power was predicted at a heart rate of 200 beats·min(-1) by regressing observed heart rates on the oxygen costs of stepping for children and youth who completed at least 2 exercise stages. Overall, despite protocol differences, we found that the aerobic fitness levels of Canadians were lower in 2007-2009 than in 1981, with declines apparent in all age and both sex groups, thereby increasing the number of those at risk of adverse health outcomes. Future work is required to validate prediction equations of aerobic fitness for young people to make it possible to compare fitness levels over the lifespan and across time.

Changes in the obesity phenotype within Canadian children and adults, 1981 to 2007-2009.

We investigated whether the relationships between BMI, waist circumference (WC), and sum of 5 skinfolds (S5S) have changed over time in Canadians. Anthropometric data on 7–69 year old from national representative surveys conducted in 1981 (n = 15,688) and 2007–2009 (n = 4,987) were examined. WC and S5S were regressed on BMI while controlling for age in each survey by sex and age group (child, adult). The results indicate that increases in WC and SFS for a one unit increase in BMI were higher in 2007–2009 than in 1981. For example, in 20–69 year old women in 1981 an increase in BMI of 1 kg/m2 was associated with corresponding increases of 1.98 cm in WC and 6.10 mm in SFS; these values increased to 2.22 cm and 7.60 mm, respectively, in 2007–2009. In conclusion, present day Canadians have higher WC and skinfold thickness values for a given BMI than Canadians did 30 years ago.

The Epidemiology of Childhood Obesity in Canada, Mexico and the United States

Published reports based on different definitions indicate that in Canada, Mexico and the United States childhood overweight and obesity have increased dramatically since 1980, with the US leading the way. The prevalence of overweight, using the International Obesity Task Force (IOTF) definitions (Cole et al. 2000) in 7–13 year old girls doubled in Canada between 1981 and 1996 and tripled in boys (Tremblay et al. 2002). In 2004 in Canada, 26% of children and adolescents aged 2–17 were overweight or obese and 8% were obese (Shields 2006). Among children under 5 years of age in Mexico, overweight prevalence (z-score of weight-for-height above +2 of World Health Organization/National Center for Health Statistics/Centers for Disease Control and Prevention (WHO/NCHS/CDC) references (Dibley et al. 1987)) increased from 4.2 to 5.3% between 1988 and 1999 (Rivera et al. 2002). In the US, between 1980 and 2006 the prevalence of high body mass index (BMI ≥95th percentile of the sex specific 2000 CDC growth charts) increased from 6 to 16% among children and teens 2 through 19 years of age (Ogden et al. 2002, 2003, 2007, 2008).

Associations between obesity and morbidity: effects of measurement methods

A recent systematic review demonstrated that self-reported data typically result in an underestimation of weight and overestimation of height (1). As a result, significant misclassification occurs when body mass index (BMI) categories are estimated from self-reported data and the prevalence of obesity is underestimated (1). Chiolero et al. (2) cautioned researchers in interpreting associations between health conditions and BMI categories when BMI is derived from self-reported values. While it may initially appear intuitive that associations between health conditions and obesity would be underestimated because of this misclassification, using a hypothetical example, Chiolero et al. demonstrated that the opposite is true – the misclassification results in an exaggerated association between obesity and diabetes (2). Using data from Statistics Canada’s 2005 Canadian Community Health Survey (CCHS), a recently published article (3) supports Chiolero et al.’s hypothetical example. The analysis was based on a sample of 2667 respondents aged 40 years or older, from whom both self-reported and measured height and weight were collected. Using logistic regression analyses, associations between BMI categories and selected health conditions were examined. Results revealed that for diabetes, high blood pressure and heart disease, the odds ratios for the overweight and obese categories were substantially higher for models based on self-reported values than those based on measured values (Table 1). Stronger associations were observed for the overweight and obese categories based on self-reported data – because the respondents in them are, in fact, more obese – than for the corresponding categories based on measured values. For example, based on measured values, 29% of respondents were classified as obese, with an average measured weight of 95 kg. Based on self-reported data, only 15% of respondents were classified as obese; however, these respondents substantially under-reported their weights, and based on measured values, their average weight was in fact 98 kg – 3 kg higher than those classified as obese based on measured data. Finally, it is important to note that although associations with obesity-related health conditions were exaggerated when BMI categories were based on self-reported data, this does not imply that the burden of disease (as measured by the number of cases) is overestimated. In fact, because the use of self-reported data underestimates the prevalence of

Obesity estimates for children based on parent-report versus direct measures

BACKGROUND Studies based on adolescents and adults have found that the use of self-reported height and weight to calculate body mass index (BMI) yields a lower prevalence of obesity than do estimates based on measured data. Relatively few studies have examined the bias resulting from the use of parent-reported height and weight for children, and the findings have been inconsistent. DATA AND METHODS Data are from the 2007 to 2009 Canadian Health Measures Survey. Parent-reported height and weight of children aged 6 to 11 (n=854) were obtained. Subsequently, the childrens height and weight were directly measured. RESULTS On average, parents underestimated the height (3.3 cm) and weight (1.1 kg) of their children. Estimates of the prevalence of obesity were significantly higher when based on parent-reported versus measured values for children aged 6 to 8; the two collection methods yielded similar estimates of obesity for children aged 9 to 11. For children in both age groups, misclassification errors for BMI categories were substantial when based on parent-reported values. This weakened associations between obesity and health indicators such as aerobic fitness and systolic blood pressure. The variance explained by factors associated with the bias in parent-reported height and weight was small, particularly for height. The use of correction equations based on variables associated with the bias resulted in a very modest reduction in misclassification errors. INTERPRETATION Bias associated with parental reports of childrens height and weight results in misclassification errors for obesity that affect relationships with other variables. Efforts to establish correction equations to adjust for this bias were unsuccessful. Direct measures are required to accurately calculate obesity estimates and their relationships with health indicators in children.