Last week, while attending the Canadian Obesity Network’s biennial Summit, I attended a lecture about childhood obesity and physical activity. One of the slides presented demonstrated a strong correlation between weight and inactivity – and the thrust of the lecture was that there was likely a strong element of causality to it.
That correlation certainly fits with the findings of the Coca-Cola funded ISCOLE trial, which examined the relationships between lifestyle and weight among over 6,000 9-11 year olds from 12 different countries and found the strongest correlation with weight was with physical activity.
But I do wonder about directionality.
Working for the past 4 years with the parents of children with obesity, I can tell you that it’s an incredibly common story to hear about the kid who used to love dance, or hockey, or soccer, or swimming – who suddenly stopped wanting to participate. Why’d they stop? Maybe because they no longer felt comfortable.
What do I mean? Take a moment and consider how you might feel about physical activity as a child if:
- Someone had made fun of how you looked in your gym clothes or uniform
- Someone had laughed at how you jiggled when you ran
- Whether anyone had ever said anything, you were self-conscious about those two points above
- You had experienced weight-related bullying in the past that made the likelihood of being bullied while exercising a credible possibility
- You were one of the slowest kids on your team, or on the track, or in the pool
- No one ever passed the ball to you
And that’s just regarding organized play and sport. The same questions would apply to active play, and so too would the question of whether or not you had friends to play with, as sadly, especially among kids with the highest weights, many don’t.
Research on the impact of childhood bullying on physical activity exists, but it’s scant. That said, it definitely supports the notion that children who are victims of bullying are less likely to be physically active (Study 1, Study 2, Study 3). Given that weight is the number one source of childhood bullying (by a substantial margin), I would love to see bullying explored as a co-variable in studies like ISCOLE, where their findings are often utilized to infer that inactivity leads kids to develop obesity, and not that obesity leads kids to become inactive. That latter directionality was found in the study Fatness predicts decreased physical activity and increased sedentary time, but not vice versa: support from a longitudinal study in 8- to 11-year-old children, which concluded,
“Our results suggest that adiposity is a better predictor of physical activity and sedentary behavior changes than the other way around.“
The ISCOLE trial, in its introduction, speaks to the existence of bullying consequent to childhood obesity, as well as obesity related social isolation – but neither are considered by the authors as possible confounding variables when it comes to inactivity. In fact, in the study’s entire discussion, this is the only mention of correlation not necessarily representing causation (for any of the examined associations)
“Finally, given the cross-sectional study design, cause-and-effect inferences cannot be made, and we cannot exclude the possibility that unmeasured confounding variables may explain some of the observed relationships.“
But given the plausible path from obesity to inactivity, along with the impact these sorts of studies have on public health and policy discussions, I sure wish it had included a more fulsome discussion therein.