Trends similar, details different
What made this study unique was their use of harmonized measures of SES – which allowed the researchers to make comparisons across countries – as well as their comparison of relative and absolute risk. Relative risk compares the risk of overweight/obesity of the low SES group to that of the high SES group. Absolute risk goes one step further by considering the percentage of these higher and lower SES groups within the population. There may be a higher relative risk (more obesity among those with low household income) but a lower absolute risk because there are fewer people overall in the low household income group compared to the entire population.
Although the trends between maternal education and household income to childhood overweight/obesity were present across all seven cohorts, the strength of the association differed between jurisdictions. McGrath points out that Quebec and Canada, for instance, have similar prevalence rates of childhood overweight (25.9 per cent, 26.6 per cent) and obesity (6.5 per cent, 7.8 per cent). However, differences were more apparent when comparing the relative and absolute risk: For relative risk, Quebec children of mothers with low educational attainment relative to those with higher education attainment at birth were about three times more likely to be obese at age 10, compared to only 1.5 times for Canadian children. Yet, when accounting for distribution of socioeconomic status across the population, Canadian children of mothers with low educational attainment or household income at birth had a higher absolute risk of being either overweight or obese at age 10. This absolute risk for Canadians was double that of Quebec children.
To solve this and other puzzles the researchers found in the data, they considered social policies that existed across provincial jurisdictions. Quebec’s generous paid parental leave programs for both mothers and fathers, higher levels of female employment, subsidized day care and lower levels of poverty may have been factors in the results, McGrath says.
Harmonized data leads to clearer understanding
“The EPOCH Collaborative Group embarked upon an ambitious project to compare birth cohorts of children across countries,” White adds. It’s a challenging task to coordinate an international collaboration and the investment yielded insightful perspectives. The EPOCH Group was especially unique because it harmonized the definition of socioeconomic variables and used identical statistics across all cohorts.”
According to White, this sets apart their findings from other studies that compare health inequalities between countries[AF1] Because they try to make sense of individual studies that used different definitions.
“Our study showed that inequality in childhood overweight and obesity varied by country when data were harmonized. This is important because it indicates that health inequality in childhood is susceptible to policy differences in countries and cannot be solely attributable to differences in the study methods,” White explains. It’s also clear that a country can be successful in reducing obesity prevalence, like the Netherlands, despite having high levels of social inequality. These findings suggest that reducing obesity in low SES children might require specific targeted policies other than those directed towards the general population.
McGrath, who holds the Chair in Childhood Preventive Health and Data Science at the PERFORM Centre, is also co-founder of the EPOCH Group.
“We’ve been investigating a series of health outcomes to see how socioeconomic circumstances and inequalities influence health early in a child’s life,” she says. “If we can identify emerging trajectories of socioeconomic inequalities already apparent in early childhood, we can think about how, when and where to target policy programming that can be implemented to optimize health and well-being and avoid health disparities later on.”
This study was partially funded by the Canadian Institutes of Health Research.
Read the cited paper: “Household income and maternal education in early childhood and risk of overweight and obesity in late childhood: Findings from seven birth cohort studies in six high-income countries.”