Potential Confounders

The etiology of obesity in childhood is complex. Socio-demographic factors, such as sex, ethnicity, household income, household education, and household food security status have been associated with obesity in children. In addition, sedentary and physical activity behaviours have been related to the development of obesity in children. Each of these factors will be briefly reviewed here.

In a longitudinal study on children’s nutrient intake and weight, Skinner et al. found that girls were more likely to have higher percent body fat than boys (Skinner, Bounds, Carruth, & Ziegler, 2003). This study was among white children 2 months until 8 years, and mostly from middle- to upper socio-economic status (Skinner et al., 2003). However, CCHS 2.2 data showed no sex difference in the prevalence of obesity among 2 to 5 year olds or 6 to 11 year olds

(Shields, 2006). Girls 12 to 17 years old had a significantly lower prevalence of overweight and obesity (combined) than boys of the same age (Table 2.2) (Shields, 2006).

Taveras et al. (2010) examined ethnic differences in early life focusing on known risk factors for obesity. This study was based in the US, and used three major ethnic groups: White, Black, and Hispanic. They found that Black and Hispanic children were more likely to have a higher intake of sugar sweetened beverages compared to White children (OR 4.11 Black, 2.48 Hispanic) and these ethnic groups had higher prevalence of BMI-for-age >95th percentile among children 3 years old (Taveras et al., 2010). Among Canadian children 2-17 years, those of Southeast/East Asian descent had lower prevalence of overweight and obesity (combined) compared to White children, however there was uncertainty in this estimate (Shields, 2006). Canadian Aboriginal off-reserve children had a higher prevalence of overweight and obesity (combined) compared to White children (Shields, 2006). Despite oversampling of Aboriginal Canadians in CCHS 2.2, some authors state that indigenous populations included in national surveys is inadequate (Ruben, 2009). Data on the prevalence of overweight and obesity among on-reserve Aboriginal children is often limited to specific communities and thus not

representative of Canada (Willows, 2005).

Socio-economic factors have also been associated with childhood overweight and obesity. Murasko et al., using NHANES 1999-2006 data, found an inverse relationship between family socio-economic status and prevalence of childhood overweight and obesity among 2-19 year

olds, where those with higher income (adjusted for inflation) had lower risk of overweight and obesity (Murasko, 2009). Similar results were found where high parental income and education was associated with lower body weight among young children (Bhargava, Jolliffe, & Howard, 2008). Some have found that the prevalence of overweight and obesity is increasing at a faster rate among US children living in low-socio-economic households compared to the total population (Singh, Siahpush, & Kogan, 2010). Among children in Canada, those who lived in households with income that was considered low-middle, middle, or upper-middle had a higher prevalence of overweight and obesity (combined) compared to children in high income

households (Shields, 2006). In addition, Canadian children living in households where the highest level of education was less than secondary school graduation had higher prevalence of overweight and obesity compared to those children living in higher education households (Shields, 2006).

Food security “exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life” (Agriculture and Agri-Food Canada, 1998). Food insecurity is the absence of food security. In Canada, 13% of households with children less than 6 years old experience food insecurity, and 15% of households with three or more children experience food insecurity (Health Canada, 2007b). Food insecurity often occurs when food is difficult to access during times of limited finances but does not necessarily mean that people are hungry, rather they may compromise their food choices and thus nutrient adequacy (Kirkpatrick & Tarasuk, 2007). However, caregivers who experience food insecurity often protect their children from food insecurity by sacrificing their own dietary intake (McIntyre et al., 2003). Despite this, food insecurity has been associated with overweight among children, especially girls 2 to 5 years of age (Metallinos-Katsaras, Sherry, & Kallio, 2009). Others have found no relationship between overweight and food insecurity among children (Bhargava et al., 2008; Gundersen, Lohman, Garasky, Stewart, & Eisenmann, 2008), and adolescents (Lohman, Stewart, Gundersen, Garasky, & Eisenmann, 2009).

Physical and sedentary activity levels are important considerations when examining the overweight and obesity among children. Skinner et al. (2003) completed a longitudinal study on children 2 months until 8 years old, and found that sedentary activity was positively related to percent body fat. National level data from the US between 1999-2006 have shown that sedentary

activities such as television viewing or computer use were more common among overweight or obese youth (Fulton et al., 2009). Similarly, among Canadian children 6 to 11 years, those who spend more than two hours per day at a computer or watching television have a higher

prevalence of overweight and obesity compared to children who have less than or equal to one hour of screen time (Shields, 2006). Among adolescents 12-17 years, those who spent more than 20 hours per week in front of a screen (television or computer) had a higher prevalence of overweight and obesity compared to those who had less than 10 hours per week of screen time (Shields, 2006). The prevalence of overweight and obesity among 6 to 11 year olds was not significantly different between children who had different levels of physical activity (Shields, 2006).