Ten-year trends in overweight/obesity among Ontario middle and high school students and their use in establishing baseline measures for government reduction targets.
Allison, Kenneth R. ; Irving, Hyacinth M. ; Adlaf, Edward M. 等
Widespread concern in the public health community about increasing
levels of overweight and obesity among children and youth has resulted
in the development of a number of policy and program initiatives
designed to address this problem in Canada and elsewhere. (1-4) For
example, in 2012, the Ontario government established the ambitious
target of reducing childhood obesity by 20% within five years. (5)
Subsequently, the Ministry of Health and Long-Term Care (MOHLTC)
established the Healthy Kids Panel, which outlined a strategy for
achieving this target by the year 2018 through a number of approaches
aimed to benefit children and youth. (6) More recently the Ministry
announced funding to 45 communities in Ontario for the Healthy Kids
Community Challenge, designed to address the issue of childhood obesity
through community-based interventions to promote physical activity,
healthy eating and adequate sleep. (7) Given the health concerns
regarding child obesity and governmental responses to address this
issue, it is important to ensure that overweight and obesity levels
among children and youth are tracked over time, and that policy and
program interventions, including natural experiments, (8) are assessed
in relation to stability and change in prevalence. (8-10)
Shield's earlier (2006) study on trends in Canada, using the
International Obesity Task Force (IOTF) criteria, describes large and
significant increases in the prevalence of overweight and obesity (based
on direct measures of height and weight in calculating body mass index
[BMI]) among youth (aged 12-17) between 1978-79 (14% combined overweight
and obesity) and 2004 (29% combined). (11) A more recent assessment of
obesity among Canadian youth (aged 12-17), based on the 2009 and 2011
waves of the Canadian Health Measures Survey, indicates the prevalence
of combined overweight and obesity to be 26.9% (IOTF cut-points) or
30.1% (World Health Organization [WHO] cut-points) with higher levels
among males. (12)
There have been no representative Ontario-level reports of trends
in overweight/obesity for specific age by sex subgroups of children and
youth based on either directly measured or self-reported height and
weight. For example, while provincial estimates based on self-reported
data from the Canadian Community Health Survey are analyzed in broad age
groups (e.g., 12-17), the sample size is not sufficient to provide
stable estimates within age and sex subgroups. In this paper we have two
objectives. First, we examine 10-year (2003-2013) trends in the
prevalence of overweight or obesity derived from self-reported height
and weight among Ontario youth, based on data from the Ontario Student
Drug Use and Health Survey (OSDUHS) and using the IOTF criteria
cut-points. This trend analysis provides the context for our second
objective. We establish data from the 2013 cycle of the survey to serve
as baseline for subsequent tracking of progress in attaining the
MOHLTC's 20% reduction target and for the assessment of
provincial-level interventions designed to reach that target.
METHODS
Study design
Our trend analyses were conducted using a stacked dataset
accumulating six cycles for the period covering surveys in years 2003,
2005, 2007, 2009, 2011 and 2013. Self-reported height and weight data
were collected during each of these survey years. The multi-year
microdata contain information on 38,407 students enrolled in 778 schools
(stage 1 primary sample unit clusters) distributed among 78
region-by-school level-by-year strata. See Kish (13) and Korn and
Graubard (14) for more detail on combining multiple complex surveys.
Each cycle was based on a target sample of 7th-12th graders enrolled in
provincially funded English and French language schools in the public
and Catholic school sectors in Ontario. Students excluded as being
out-of-scope were those in private schools; those schooled in
correctional or health facilities; students schooled on First Nations
reserves, military bases and in remote areas of Northern Ontario; and
the few who were home-schooled. These exclusions represented roughly 8%
of all Ontario children and adolescents aged 12 to 18. Each cycle was
selected by means of a stratified, two-stage (school then class) cluster
design. In stage 1, schools (stratified by region and school level) were
selected by systematic random sampling according to
probability-proportionate-to-school size, followed by a within-school
selection of one class per stratified grade selected with equal
probability.
For the period under study, the school response rate (number
participating/number selected) varied from 49% to 71% (mean = 60%), the
class response rate varied from 80% to 98%, and the conditional (on
school and class participation) student response rate (number
participating/number of students enrolled in recruited classes) fell
from 72% to 63% and was strongly related to an increase in the loss of
parental consent, which rose from 16% to 26% (an increase that occurred
among all grades and regions). (15) An appraisal of the potential
nonresponse bias in the 2013 cycle showed very few differences in key
health indicators (e.g., drug use, mental health, physical health)
between the 294 classes with a response rate 70% or higher versus the
377 classes with lower response rates. (15)
In each cycle, active parental consent and student assent
procedures were required. To maximize data collection during a fixed
(regularly scheduled) classroom period while minimizing the number of
items per questionnaire, the OSDUHS uses two forms, which are
distributed alternately in classrooms. Students completed the
paper-pencil questionnaires anonymously during regular class time. Staff
from the Institute for Social Research at York University administered
the questionnaires and processed all data. Each cycle of the OSDUHS was
approved by the Research Ethics Boards of the Centre for Addiction and
Mental Health, and York University.
Measures
For students aged 12-18, overweight/obesity status was derived from
age- and sex-specific self-reported height and weight, from which BMI
was computed and applied to the IOTF-defined classifications
(Cole/IOTF). For students aged 19 years or older, weight status was
based on the international classification of adult weight status
(http://apps.who.int/bmi/index.jsp?introPage=intro_3.html).
In the three cycles between 2003 and 2007 the height and weight
questions were included in one of the two questionnaire forms, presented
in an open-ended response format. Students recorded their numeric weight
in pounds or kilograms and their height in feet or centimetres.
Beginning in 2009, the height and weight questions were included in both
questionnaire forms. Also, beginning in 2007, the questionnaire used
pre-coded response options. The height question provided 27 options in
feet/centimetres. The weight question provided 42 options in 5 lb (or
equivalent kilogram) intervals. Using the midpoint of the height and the
weight response categories, BMI was calculated as weight in kilograms
divided by height in metres squared. Students without valid height or
weight information were excluded from the analysis. The proportion of
missing height or weight in 2003 and 2005 was 9.6% and 8.8% respectively
of the estimation sample. Missing height and weight between 2007 and
2013 ranged from 4.6% to 6.2% of the estimation sample. Further details
regarding OSDUHS methodology can be accessed at
http://www.camh.ca/research/osduhs.aspx.
Statistical analysis
Our analyses employed design-based methods to account for the
complex survey data of the OSDUHS. This estimation differs from
non-survey analysis in two respects. First, pseudo-maximum likelihood
estimation is employed in the estimation of point estimates (because the
assumptions of ordinary maximum likelihood estimation are violated with
stratified, clustered data) and, second, Taylor series linearization is
employed in the estimation of variances. (14,16) Sample weights were
used in all analyses to account for the unequal inclusion probabilities
due to disproportional stratification and sponsored oversampling of
select regions, and for nonresponse and sex/grade/region
post-stratification adjustments. To estimate provincial trends, for each
logit model the binary overweight/obesity response was regressed on four
factors--a linear and quadratic time trend, and sex and grade
covariates. Both linear and quadratic terms are presented. In addition
to time factors, sex and grade (measured by a single binary indicator
[G7 vs. G8] for the middle school subsample and three dummy variables
representing grades 10 through 12 [vs. G9] for the high school
subsample) were modeled as covariates. Subsamples were selected using
the subpopulation selection methods necessary to achieve correct
variance estimates, (17) and normalized weights scaled to the number of
respondents were applied for multi-year analysis. (14) The analytic
sample size was 36,058 (38,407 minus 2,349 with missing data). All
analyses were computed using complex survey estimation procedures
implemented in Stata version 13. (18)
RESULTS
Trends in overweight/obesity among middle school students
Table 1 summarizes the results of our trend analyses among middle
school students. From 2003 through 2013, no significant change occurred
in the provincial prevalence of overweight/ obesity (21.2%-21.6%).
Moreover, this finding held across all sex, grade and grade-sex
subgroups, except 7th-grade females, whose prevalence of
overweight/obesity showed a significant linear decline from 23.9% in
2003 to 15.8% in 2013.
Trends in overweight/obesity among high school students
The results of our trend analyses among high school students are
presented in Table 2. From 2003 to 2013, the provincial prevalence of
overweight/obesity showed a weak but statistically significant linear
increase (23.7%-26.1%). Significant linear increases were also evident
among 11th graders (22.4%-28.9%), females (17.1%-22.4%), and 10th
(14.8%-24.2%) and 11th-grade females (17.0-25.2%). However, the
prevalence of overweight/obesity held steady from 2003 through 2013
among 9th- and 12th-grade females as well as among males in all grades.
Baseline overweight/obesity in relation to the MOHLTC reduction
target
On the basis of the 2013 OSDUHS data, 25.1% (95% confidence
interval: 23.5-26.7) of students in grades 7 through 12 were classified
as overweight or obese (Figure 1). We used this prevalence estimate as
the baseline to set a presumed target of 20.1%, representing the 20%
improvement in five years set by the provincial government. The
provincial picture at baseline masks substantial subgroup variability in
the prevalence of overweight/ obesity in 2013. For example, among middle
school students, 7th-(15.8%) and 8th-grade (17.3%) females surpassed the
provincial target; however, 7th-(26.2%) and 8th-grade (26.6%) males did
not. Among high school students, only 12th-grade females (19.7%) met the
target, and 9th-grade females (21.1%) were near to the target set for
2018. Overweight/obesity levels among females in the 10th (24.2%) and
11th (25.2%) grades, as well as among males in the 9th (26.9%), 10th
(31.2%), 11th (32.5%) and 12th (28.1%) grades, were higher than the
specified goal (Figure 1).
DISCUSSION
While the results of our trend analyses indicate that the
prevalence of overweight/obesity stabilized among select demographic
subgroups between 2003 and 2013, the prevalence in 2013 remained
elevated, especially among males (range: 26.2% of 7th graders to 32.5%
of 11th graders). The higher prevalence of overweight/obesity among
males is consistent with other studies of this age group, (1,11) raising
questions regarding the reasons for this finding as well as challenges
around how best to address the issue. Of equal concern is the increasing
prevalence in overweight/ obesity between 2003 and 2013 among particular
subgroups, including grade 10 and 11 females. Only grade 7 females were
found to have a lower prevalence during the 10-year period. While this
finding is difficult to explain, it may suggest a positive change and
needs to be confirmed by examining trends in future waves of the survey.
The results contrast with a recent study on trends in the
prevalence of obesity in the US, which found no significant increases in
prevalence among youth (aged 12-19) between 2003-2004 and 2011-2012.
(19) Although the prevalence in that study is elevated from a public
health standpoint (20.5% obesity and 34.5% combined overweight or
obesity based on directly measured height and weight and the Centers for
Disease Control and Prevention [CDC] growth charts in 2011-2012), youth
obesity appears to have plateaued in that country, although further data
points are required to confirm this.
The results of our analyses indicate that, as of 2013, females in
the 7th, 8th, 9th and 12th grades are currently well positioned relative
to the MOHLTC presumed five-year target of 20.1%. However, 10th- and
11th-grade females and males in all grades are poorly positioned
relative to the target. Will the current cohort of 7th- and 8th-grade
females continue to maintain and carry forward a lower prevalence of
overweight and obesity as they transition to secondary school? Or will
this group trend upward with increasing school grade/age? If the 7th and
8th grade males carry forward their current rates of overweight and
obesity (26.2% and 26.6% respectively), will they resemble and replace
the 2013 cohort of overweight/obese male high school students or trend
downwards, given a range of initiatives at the federal,
provincial/territorial and municipal levels? These are questions that
the current trend analyses raise. The results also suggest that if the
MOHLTC five-year target is to be realized substantial policy and
practice initiatives will be required. A factor related to the context
of these analyses is that the 2018 target year established in the
Healthy Kids Panel report (6) may subsequently be extended by the
MOHLTC, since interventions to address childhood overweight and obesity
are unfolding over time. In any case, our use of the 2013 OSDUHS serves
as an appropriate baseline for ongoing monitoring of this age group.
An important issue relevant to policy and programs is the need for
more specific clarification around the provincial government targets.
For example, while the target of a 20% reduction of child obesity within
five years is based on a provincial reduction in overweight/obesity
prevalence, it is not clear whether this target also applies within
particular age or age/sex subgroups. This is an important issue for
those evaluating progress on the target outcome. We found in our
analysis that provincial stability and change in levels of overweight
and obesity mask cohort differences by grade and sex. In particular, it
may be important for the provincial government to consider developing
and monitoring different targets for different cohorts. Similarly, it is
important to monitor potential harms associated with a focus on reducing
overweight and obesity, for example, trends in the prevalence of poor
body image, obesity-related stigma, and bullying and disordered eating
in this population. (20) In addition, emphasis should be placed on
monitoring contextual and environmental factors that encourage positive
health behaviours, including healthy weights. (21) Several relevant
variables (e.g., body image, weight control, use of diet pills, fruit
and vegetable consumption, physical activity and sedentary behaviour)
are available in the OSDUHS data.
Our findings must be appraised in light of the study limitations.
First, the findings are based on calculations of BMI from self-reported
height and weight, which tend to underestimate levels of overweight and
obesity in comparison to direct physical measures. (10,22-25) Second, it
was not possible to conduct separate analyses for overweight and obesity
because of an insufficient number of cases in specific age and sex
subgroups. Existing studies that analyze overweight and obesity
separately normally need to combine ages into broader age categories.
(1,11,12,19)
A third limitation is that there were a few inconsistencies in the
data. For example, in 2007, grade 7 and 8 females had higher rates of
overweight/obesity than males--a finding that runs counter to the
results from other years. We cannot explain specific examples of
inconsistency in the data. However, we acknowledge that changes in how
the data were collected in 2007 may partly explain this. According to
the most recent OSDUHS report, (15 p 49) "experimental work on the
OSDUHS showed that the pre-coded format reduced missing value responses
versus open-ended formats". This may have had some effect on
inconsistencies in the earlier (prior to pre-coding) years.
A fourth limitation is that the inclusion of secondary school
students over age 18 does not correspond directly to the upper end of
the MOHLTC target (presumably age 17 or 18). However, the OSDUHS
estimates based on grade level do correspond to various stages in the
life course and student "career". Thus it is useful to retain
the grade subgroup sample (including those 18+) in the analysis of
overweight/obesity over time. Furthermore, the MOHLTC is not conclusive
in its designation of the age range targeted in its goal.
As mentioned earlier, we applied the IOTF criteria cut-points to
categorize overweight and obesity status. Comparisons among the WHO,
IOTF and CDC cut-points, based on directly measured height and weight,
found that both the IOTF and CDC cut-points underestimate the prevalence
of overweight and (especially) obesity among children and youth. (10)
While current research on the prevalence of population overweight and
obesity has yet to accept a single classification system, the IOTF
criteria were the most frequently used in a recent systematic review of
the prevalence of overweight and obesity in adolescents aged 10-19.26
The recent scientific literature acknowledges that both the IOTF and WHO
criteria can be used to assess BMI among children and youth. (1,10,12)
In summary, both the IOTF and WHO criteria have been recommended for
assessment of trends in the prevalence of overweight and obesity.
(10,27)
The strengths of our study include the use of representative
samples of Canadian middle and high school students at a provincial
level and the assessment of overweight/obesity at biennially repeated
intervals over a 10-year period. Moreover, repeated data allow one to
construct evaluation models not only with both pre and post data points
but also with multiple preprogram data points, which would strengthen
the interpretation of program effect. Lastly, the sufficiently large
samples allow for the identification of subgroups that may be less
likely to achieve target reduction objectives.
In summary, this study documents 10-year trends in overweight and
obesity among Ontario middle and high school students. These patterns
indicate provincial stability in the prevalence of overweight/obesity
among middle school students and a statistically significant provincial
increase for high school students. In addition, the study demonstrates
the potential contribution of an existing data system capable of
monitoring progress on meeting the MOHLTC target. Finally, it
demonstrates the need to investigate subgroup variation, which may not
only mitigate the ability of achieving the desired target but would also
identify groups in need of enhanced or tailored policy and program
interventions.
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Received: June 18, 2015
Accepted: October 11, 2015
Kenneth R. Allison, PhD, [1,2] Hyacinth M. Irving, MA, [3] Edward
M. Adlaf, PhD, [2,4] Guy E.J. Faulkner, PhD, [5,6] Angela Boak, MA, [4]
Heather E. Manson, MD, [1,2] Hayley A. Hamilton, PhD, [2,4] Bessie Ng,
MPH [7]
[1.] Department of Health Promotion, Chronic Disease and Injury
Prevention, Public Health Ontario, Toronto, ON
[2.] Dalla Lana School of Public Health, University of Toronto,
Toronto, ON
[3.] Centre for Global Health Research, Li Ka Shing Knowledge
Institute, St. Michael's Hospital, Toronto, ON
[4.] Social and Epidemiological Research Department, Centre for
Addiction and Mental Health (CAMH), Toronto, ON
[5.] School of Kinesiology, University of British Columbia,
Vancouver, BC
[6.] Faculty of Kinesiology and Physical Education, University of
Toronto, Toronto, ON
[7.] Region of Waterloo Public Health and Emergency Services,
Waterloo, ON
Correspondence: Kenneth R. Allison, PhD, Kr Allison Research
Consulting, 575 Windermere Avenue, Toronto, ON M6S 3L9, Tel:
416-604-7084, E-mail: ken.allison@rogers.com
Acknowledgements: We acknowledge Public Health Ontario for
contribution to publication costs.
Conflict of Interest: None to declare.
Table 1. Trends in the prevalence of overweight/obesity (IOTF
defined) among Ontario middle school students, Ontario Student
Drug Use and Health Survey, 2003-201 3,
n = 11,326
2003 2005
% (95% CI) n % (95% CI) n
Overall 21.2 (7.4-25.6) 751 23.4 (20.4-26.6) 770
Females 19.6 (14.8-25.5) 401 18.9 (15.3-23.1) 370
Males 23.2 (17.8-29.5) 350 27.3 (22.4-32.9) 400
Grade 7 23.3 (17.9-29.8) 357 21.2 (17.8-25.1) 362
Grade 8 19.1 (14.8-24.4) 394 25.3 (20.6-30.6) 408
Grade 7 females 23.9 (16.4-33.6) 193 17.1 (12.2-23.3) 185
Grade 8 females 15.1 (9.7-22.8) 208 20.8 (15.7-27.0) 185
Grade 7 males 22.5 (16.3-30.2) 164 25.5 (19.4-32.7) 177
Grade 8 males 23.7 (17.4-31.6) 186 28.8 (21.2-37.8) 223
2007 2009
% (95% CI) n % (95% CI) n
Overall 19.8 (17.0-23.0) 624 25.5 (22.9-28.2) 2926
Females 20.8 (16.1-26.5) 339 20.6 (17.5-24.2) 1549
Males 18.8 (15.1-23.1) 285 29.9 (26.3-33.9) 1377
Grade 7 22.2 (17.7-27.6) 296 23.5 (20.0-27.4) 1398
Grade 8 17.5 (13.3-22.8) 328 27.4 (24.4-30.6) 1528
Grade 7 females 23.8 (16.2-33.5) 156 18.9 (14.4-24.5) 730
Grade 8 females 18.2 (13.2-24.7) 183 22.3 (18.6-26.4) 819
Grade 7 males 20.8 (15.2-27.9) 140 27.7 (21.9-34.3) 668
Grade 8 males 16.8 (10.9-25.0) 145 32.1 (28.2-36.2) 709
2011 2013
% (95% CI) n % (95% CI) n
Overall 20.4 (18.0-23.0) 2612 21.6 (18.5-25.1) 3643
Females 15.9 (12.8-19.5) 1364 16.6 (13.4-20.3) 1924
Males 24.7 (21.7-28.0) 1248 26.4 (21.6-31.9) 1719
Grade 7 19.7 (16.1-24.0) 1274 21.1 (17.0-25.9) 1810
Grade 8 20.9 (18.0-24.2) 1338 22.1 (19.2-25.2) 1833
Grade 7 females 15.9 (11.9-20.8) 666 15.8 (12.1-20.5) 967
Grade 8 females 15.8 (11.7-21.1) 698 17.3 (12.5-23.4) 957
Grade 7 males 23.5 (18.6-29.3) 608 26.2 (18.1-36.4) 843
Grade 8 males 25.8 (21.6-30.5) 640 26.6 (22.2-31.5) 876
p value for p value for
linear quadratic
trend trend
(2003-2013) (2003-2013)
Overall 0.632 0.346
Females 0.092 0.278
Males 0.461 0.601
Grade 7 0.372 0.901
Grade 8 0.875 0.116
Grade 7 females 0.044 0.839
Grade 8 females 0.694 0.148
Grade 7 males 0.607 0.870
Grade 8 males 0.575 0.478
IOTF defined, International Obesity Task Force body mass
index cut-offs; CI, confidence interval.
2003-2007 cycles based on half samples; sample sizes are
unweighted; prevalence rates are weighted estimates; trend
analyses are based on logistic regression modeling linear
and quadratic time effects with sex and grade covariates.
Table 2. Trends in the prevalence of overweight/obesity
(IOTF defined) among Ontario high school students,
Ontario Student Drug Use and Health Survey, 2003-2013,
n = 24,732
2003
% (95% CI) n
Overall 23.7 (21.6-26.0) 2112
Females 17.1 (14.7-19.8) 1093
Males 30.5 (27.2-34.1) 1019
Grade 9 24.0 (19.9-28.6) 556
Grade 10 23.8 (19.8-28.3) 533
Grade 11 22.4 (18.6-26.8) 540
Grade 12 24.9 (20.2-30.3) 483
Grade 9 females 20.2 (16.5-24.4) 282
Grade 10 females 14.8 (10.9-19.8) 293
Grade 11 females 17.0 (12.5-22.6) 273
Grade 12 females 16.7 (11.8-23.0) 245
Grade 9 males 27.9 (20.3-36.9) 274
Grade 10 males 34.5 (27.9-41.9) 240
Grade 11 males 27.8 (22.7-33.5) 267
Grade 12 males 32.4 (25.0-40.8) 238
2005
% (95% CI) n
Overall 23.9 (21.7-26.2) 2558
Females 17.7 (15.0-20.8) 1327
Males 29.6 (26.4-32.9) 1231
Grade 9 23.6 (19.8-28.0) 633
Grade 10 23.0 (19.6-26.7) 637
Grade 11 24.9 (21.5-28.7) 683
Grade 12 24.0 (20.1-28.4) 605
Grade 9 females 15.8 (12.1-20.3) 342
Grade 10 females 15.9 (11.9-20.8) 340
Grade 11 females 23.9 (18.4-30.5) 340
Grade 12 females 15.2 (10.3-21.8) 305
Grade 9 males 30.9 (25.5-36.9) 291
Grade 10 males 29.7 (25.0-34.7) 297
Grade 11 males 25.9 (21.0-31.6) 343
Grade 12 males 31.2 (25.4-37.8) 300
2007
% (95% CI) n
Overall 24.6 (22.5-26.8) 2170
Females 17.8 (15.2-20.6) 1075
Males 30.5 (27.3-34.0) 1095
Grade 9 23.2 (19.4-27.4) 521
Grade 10 26.3 (22.3-30.9) 509
Grade 11 25.6 (21.7-29.9) 576
Grade 12 23.6 (19.9-27.7) 564
Grade 9 females 17.0 (12.8-22.2) 254
Grade 10 females 18.5 (13.8-24.4) 241
Grade 11 females 18.2 (13.2-24.6) 285
Grade 12 females 17.5 (13.1-22.9) 295
Grade 9 males 28.8 (22.8-35.6) 267
Grade 10 males 33.2 (27.3-39.6) 268
Grade 11 males 32.3 (26.5-38.7) 291
Grade 12 males 28.5 (23.3-34.2) 269
2009
% (95% CI) n
Overall 25.2 (23.5-26.9) 5649
Females 19.9 (18.0-22.1) 2921
Males 30.0 (27.1-33.1) 2728
Grade 9 26.1 (22.9-29.5) 1375
Grade 10 25.8 (23.0-28.9) 1504
Grade 11 25.4 (21.7-29.5) 1343
Grade 12 23.8 (20.7-27.2) 1427
Grade 9 females 20.9 (15.3-27.8) 716
Grade 10 females 21.5 (18.1-25.3) 773
Grade 11 females 20.0 (16.8-23.7) 712
Grade 12 females 17.9 (13.6-23.1) 720
Grade 9 males 30.9 (27.2-34.9) 659
Grade 10 males 30.0 (25.7-34.7) 731
Grade 11 males 30.5 (24.4-37.4) 631
Grade 12 males 29.0 (24.4-34.0) 707
2011
% (95% CI) n
Overall 27.3 (24.5-30.2) 6249
Females 23.1 (20.1-26.4) 3404
Males 31.1 (27.8-34.7) 2845
Grade 9 27.2 (22.1-33.1) 1632
Grade 10 27.7 (23.7-32.1) 1508
Grade 11 28.7 (25.0-32.6) 1508
Grade 12 25.9 (22.2-30.1) 1601
Grade 9 females 22.8 (16.2-31.0) 856
Grade 10 females 24.8 (19.1-31.7) 823
Grade 11 females 24.9 (20.0-30.6) 842
Grade 12 females 20.6 (17.2-24.4) 883
Grade 9 males 31.5 (26.2-37.2) 776
Grade 10 males 30.4 (24.8-36.8) 685
Grade 11 males 32.2 (26.2-38.8) 666
Grade 12 males 30.6 (25.0-36.9) 718
2013
% (95% CI) n
Overall 26.1 (24.2-28.0) 5994
Females 22.4 (20.2-24.6) 3381
Males 29.6 (26.6-32.7) 2613
Grade 9 24.0 (21.2-27.1) 1476
Grade 10 27.8 (23.8-32.1) 1506
Grade 11 28.9 (25.3-32.8) 1534
Grade 12 24.2 (21.3-27.4) 1478
Grade 9 females 21.1 (17.5-25.1) 850
Grade 10 females 24.2 (20.8-27.9) 842
Grade 11 females 25.2 (20.3-30.8) 884
Grade 12 females 19.7 (16.3-23.7) 805
Grade 9 males 26.9 (22.1-32.3) 626
Grade 10 males 31.2 (24.8-38.3) 664
Grade 11 males 32.5 (27.7-37.7) 650
Grade 12 males 28.1 (24.2-32.3) 673
p value for p value for
linear trend quadratic
(2003-2013) trend
(2003-2013)
Overall 0.022 0.781
Females <0.001 0.924
Males 0.935 0.774
Grade 9 0.564 0.416
Grade 10 0.094 0.986
Grade 11 0.008 0.949
Grade 12 0.788 0.884
Grade 9 females 0.139 0.875
Grade 10 females <0.001 0.446
Grade 11 females 0.030 0.676
Grade 12 females 0.092 0.970
Grade 9 males 0.749 0.246
Grade 10 males 0.660 0.570
Grade 11 males 0.114 0.809
Grade 12 males 0.418 0.841
Note: IOTF defined, International Obesity Task Force
body mass index cut-offs; CI, confidence interval.
2003-2007 cycles based on half samples; sample sizes
are unweighted; prevalence rates are weighted
estimates; trend analyses are based on logistic
regression modeling linear and quadratic time
effects with sex and grade covariates.
Figure 1. Prevalence of overweight/obesity
(based on International Obesity Task Force
cut-offs) among Ontario middle and high school
students, Ontario Student Drug Use and Health
Survey (SDUHS), 2013
Female Male
Middle school
Grade 7 15.8 26.2
Grade 8 17.3 26.6
High school
Grade 9 21.1 26.9
Grade 10 24.2 31.2
Grade 11 25.2 32.5
Grade 12 19.7 28.1
Note: The red line at 25.1% represents the baseline prevalence
of overweight/obesity among 7th-12th grade students in the 2013
OSDUHS.
The green line at 20.1% represents the 20% decrease (from 2013)
that the Ontario Government is attempting to achieve by 2018.
Note: Table made from bar graph.
