Obesity in Canada – Prevalence among children and youth

Prevalence Among Children and Youth

Many of the physical and psychological complications and comorbidities of obesity may begin during childhood.^{Footnote 21} According to the 2006 Canadian clinical practice

guidelines on the management and prevention of obesity in adults and children, it can be more challenging to identify obesity among children and youth than among adults, as body composition and anthropometric indicators change with normal growth and maturation.^{Footnote 22} The calculation of BMI is the same as for adults, but the cut-offs for weight status vary by age and sex.^{Footnote 22} For example, using the International Obesity Task Force (IOTF) system the BMI cut-off for the obese class would be 21.22 kg/m² for a 12-year-old boy and 26.02 kg/m² for a 12-year-old girl.^{Footnote 23}

There are also different systems of BMI cut-offs, and obesity estimates can vary among systems. For example, using the IOTF system obesity among children and youth aged 2 to 17 in the 2004 CCHS was 8.2%. However, obesity in this age group was 12.7% based on the WHO child growth standards (0-5 years) and growth reference (5-19 years), or 12.5% based on US Centers for Disease Control and Prevention (CDC) cut-offs. The size of the difference between estimates also appears to vary by age group.^{Footnote 24}

Estimates of obesity cited in this report, derived from CCHS and CHMS data for the population 18 and under, were produced using age-specific IOTF cut-offs.

Among children and youth aged 6 to 17, the prevalence of obesity was 8.6% according to the 2007-2009 CHMS.^{Footnote 25} Measured obesity by age and sex for the CHMS as well as for CCHS 2004 is shown in Table 1. Obesity is similar by sex in the youngest age group, but in older age groups it appears to be more common among males than females. The prevalence of obesity tends to increase by age group, as was the case for adults.

Source: Canadian Community Health Survey 2004 sourced from Shields,^{Footnote 26} Canadian Health Measures Survey.^{Footnote 25}

Change over time

The prevalence of measured obesity was 2.5 times higher in 2004 than 1978/79 among children and youth aged 2 to 17.^{Footnote 26} In particular, among youth aged 12 to 17 obesity tripled from 3% to 9.4%.^{Footnote 26} Increases in childhood obesity have been reported using BMI,^{Footnote 26} waist circumference and skin fold measurements.^{Footnote 27} Further, results from the CHMS suggest that increases in BMI among children and youth are associated with greater adiposity, rather than greater muscularity.^{Footnote 27}

While measured obesity has increased in the last decades, between 2000 and 2008 self-reported obesity among youth aged 12 to 17 has been relatively stable (Figure 7). As is the case with adults, self-reported obesity prevalence tends to be lower than measured estimates.

Figure 7: Prevalence of Self-Reported Obesity by Sex, Ages 12 to 17, 2000-2007/08

Source: Analysis of the 2000, 2003, 2005 and 2007/08 Canadian Community Health Surveys, Statistics Canada.

Key points

• Measured obesity is 8.6% among children and youth aged 6 to 17, and earlier estimates suggest that 6.3% of children aged 2 to 5 are obese.
• Measured obesity has increased 2.5 times in the last decades.
• Studies suggest that these increases in obesity may reflect increases in adiposity, rather than increases in muscularity.
• Self-reported obesity has been stable among youth aged 12 to 17 in the last few years.
• As with adults, self-reported obesity is lower than measured values.
• In most age groups of children and youth, according to self-reported and measured data, obesity is more prevalent among boys than girls.
• There are a number of research gaps and methodological challenges in studying obesity in this population, including different systems for defining overweight and obesity at different ages and the study of prevalence among very young children.
• The development of improved measurement, ongoing surveillance and longitudinal studies could help to enhance the understanding of obesity in children and youth.