Today’s guest post comes from friend and colleague Dr Katya Herman, and describes her recent paper in the journal Preventive Medicine. This study was done using the QUALITY cohort, which is a very useful dataset for studying the relationships between sedentary behaviour/physical activity and health in the pediatric age group (this is the same dataset that we used for my recent paper on the health impact of breaks in sedentary time). You can find more on Katya at the bottom of this post.
By now we’ve all heard that being too sedentary isn’t just another way of saying we are inactive – in fact, it is possible to accumulate enough physical activity for health benefits, yet still be too sedentary, depending on what we are doing for the other 23+ hours of our day, referred to as being an “active couch-potato”. We also know that too much sedentary behaviour (including screen time, use of passive/motorized transportation, and other instances of sitting/reclining for long periods) is detrimental to our health, independently from the health benefits we might achieve from being “active” people.
On average, Canadian children spend almost 9 hours per day (over 60% of their waking hours) sedentary, including a high amount of screen time. This screen time especially has been found to be associated with weight status and obesity in children. Until now, few research studies had attempted to describe sedentary behaviour in children using both objective (accelerometers) and subjective (child self-report) information together. Hence this is what we set out to do, in young children who were at elevated risk for obesity due to having at least 1 obese parent.
What we did
A group of 534 kids ages 8-10 from the QUebec Adipose and Lifestyle InvesTigation in Youth (QUALITY) study wore an Actigraph accelerometer for 1 week to measure both their sedentary and physical activity time. They also answered questions about the number of hours/day (both weekdays and weekends) they usually watched television or movies, used the computer for fun or playing video games, did homework, read for fun and talked on the phone. Therefore we were able to calculate the proportion of their total sedentary time accounted for by the specific behaviours they reported, the association between high sedentary time and overweight/obesity, and the proportion of kids who fell into the “active couch-potato” category as well as other physical activity/sedentary combinations.
What we found
In this group of kids, only 56% of girls and 38% of boys reported 2 hours or less screen time per day, as recommended by the Canadian Sedentary Behaviour Guidelines. At the same time, only 46% of boys and a paltry 15% of girls accumulated the 60 min/day of moderate-to-vigorous physical activity recommended by the Canadian Physical Activity Guidelines. Overweight or obese kids accumulated 18 min/day more total sedentary time and reported on average 36 min/day more screen time than normal weight kids, and also had lower physical activity levels.
We found that anywhere from 19-43% of total sedentary time (measured by accelerometer) was not accounted for by the specific behaviours the children reported, and this unexplained sedentary time was highest in girls and in the most sedentary boys. The pie charts below show the breakdown of sedentary behaviours reported by the boys (top row) and girls (bottom row), according to their category of total daily sedentary time (low, medium, high) measured by accelerometers.
Some of the “missing” time is likely from under-reporting of behaviours by the children, while there were also several possible behaviours not captured by the questionnaire used (e.g. socializing, eating, passive transportation). As total sedentary time increased, screen time also increased. Also, overweight and obese kids had almost twice the likelihood of being in the highest category of total sedentary time and of reporting more than 2 hours/day screen time, compared to normal weight kids.
Finally, we found that 28% of boys and 5% of girls fit into that “active couch-potato” category: these kids achieved the recommended 60 min/day of moderate-to-vigorous physical activity, yet they also reported more than 2 hours/day of screen time. Recall that only 15% of the girls in the group achieved 60 min/day of moderate-to-vigorous physical activity to be classified as “active”, so this explains the lower percentage of girls in the “active couch-potato” group. Overall it is concerning that about 60% of all the “active” boys (and 33% of “active” girls) were none-the-less “too sedentary”.
Only 19% of boys and 10% of girls were classified as both active and non-sedentary (the ideal), while over one third of the kids were both inactive and sedentary (the worst case). Compared to normal weight kids, overweight/obese kids were far less likely to achieve that ideal of being active/non-sedentary, and more likely to be inactive/sedentary.
What we concluded
We need to recognize that active kids are not immune to being too sedentary, and on the flip side, we can’t just assume that all inactive kids are automatically also too sedentary. Overweight/obese children are more sedentary and report more screen time than normal weight children. However, a significant proportion of a child’s total sedentary time isn’t accounted for by their own self-reports of their specific behaviours, especially for the most sedentary kids. Therefore we need to continue to develop ways of gathering more detailed information in order to better describe the full nature of sedentary behavior. We also need to consider sex and weight status when devising public health strategies aimed at reducing screen time and increasing physical activity in kids.
Herman KM, Sabiston CM, Mathieu ME, Tremblay A, Paradis G. Sedentary behavior in a cohort of 8- to 10-year-old children at elevated risk of obesity. Preventive Medicine, doi: 10.1016/j.ypmed.2013.12.029. Available here.
About the author: Dr. Katya Herman is an Assistant Professor in the Faculty of Kinesiology & Health Studies at the University of Regina. Her research focuses on the epidemiology of physical activity, sedentary behaviour and obesity across the lifespan, with interests in both health-related quality of life and cardiometabolic outcomes. Outside of work, she is a former national team rower, and continues to train and compete while also an NCCP Level 3 certified coach. Her faculty web page can be found here.