I write this blog near 5pm on a Monday in early January. I was slouching so much so that my bottom was at the front of my seat and my spine was curved into a C-shape, but now I am sitting better because I am aware that you will judge me if I sit poorly. Being a physical health lecturer, and all. Because you can see me, of course!

Most of us don’t even know how to ‘sit better’. We are too tired or busy to think about it, or to try. Most of us also get in a car to go to work, sit at work, get in a car to go home and sit again at home. Pretty divergent behaviour compared to that of our Stone Age ancestors. Luckily, or rather, informedly, I ride my yellow bike (with not one, but two, baskets) to and from work.

When I say most of us, I am not just talking about the older ‘us’ who can read, I also mean young children. Imagine the life of a 5-year-old Cavechild compared to a 5-year-old Modernchild. The former would be scuttling about helping his or her Cavemum forage for food and running away from woolly mammoths.  The latter plays military computer games while his over-worked Modernmum heats up a microwave meal to be served in front of the television.

We all know that there’s an overweight and obesity ‘epidemic’. In all of us, i.e. both adults and children. Recent Australian statistics report a 2011-2012 prevalence of overweight and obesity in children aged 5-17 years of 25.3%, comprised of 17.7% overweight and 7.6% obese (Source). Such figures closely follow US obesity figures from the 2009–2010 National Health and Nutrition Examination Survey of 16.9% of children and adolescents aged 2–19 years being obese (Source).

The prevention of overweight and obesity in childhood is of particular importance because, ‘healthy habits formed early in life can follow on throughout childhood, adolescence and into adulthood. Conversely, less than healthy habits established in childhood may continue into adulthood, increasing a person's associated health risks such as cardiovascular disease, high blood pressure and Type 2 diabetes’ (Source).

What are the causes of high levels of physical inactivity/sedentary behaviour and low levels of physical activity - overall less energy expenditure - in our Modernchildren? Screen time is one big reason, as has already been inferred by our Cavechild/Modernchild scenario above. Screen time is one aspect of sedentary  behaviour and can be defined as time spent sitting in front of televisions, videos, DVDs and computers. Increased screen time not only decreases energy expenditure because it invariably involves sitting, but it is often associated with increased food consumption, e.g. snacking behaviour.

Let’s look at some recent evidence of associations between screen time and body weight in children. When looking at physical inactivity, Morley et al 2012 undertook a cross-sectional survey of Australian secondary school students aged 12-17 years and showed that those engaging in more time in small screen recreation were significantly more likely to be overweight or obese (Source). And a 2012 systematic review of 23 journal articles looking at the behaviours of preschool children aged 4-6 years showed moderate evidence for a prospective positive relationship later in childhood (<18 years) between television viewing and overweight (Source).

Similarly, physical activity is often negatively associated with weight. Evidence is strong for low levels of physical activity being associated with increased overweight and obesity (Source), and high levels of physical activity being associated with decreased overweight and obesity (Source). It’s interesting to note that the weighting (pardon the pun) attributed to physical (in)activity vs nutrition in determining human body mass is hotly contested. For example, in favour of the energy expenditure side of the weighty coin, researchers from the Australian National University studied more than 700 primary school children over four years, and found that lean children were doing far more physical activity than those who were overweight, but both groups were consuming similar energy (Source).

Decreasing physical inactivity (e.g. by decreasing screen time) and increasing physical activity are obvious preventive and treatment measures for overweight and obesity in children. Prevention of course being better than cure, as well as being more effective in children - whose habits are yet to be ingrained. A Cochrane systematic review of interventions to prevent childhood obesity states, ‘Childhood obesity prevention research must now move towards identifying how effective intervention components can be embedded within health, education and care systems and achieve long term sustainable impacts.’ (Source). Think of yourself as the home aspect of the care system if you have kids.

So, what can you do to optimise a child’s home environment with respect to physical activity behaviours? Try to decrease their physical inactivity and increase their physical activity, of course. To address the screen time aspect of the former the US National Institutes of Health provides some great tips, as well as a screen time tracking chart (Source). To increase the latter, perhaps provide active video games like dancing or standing sport ones (Source), and encourage them to engage in a sport they enjoy and/or increase their active play. A recent Canadian study suggests that in children achieving more than seven minutes of vigorous physical activity daily there is a reduced risk of overweight (Source). Finally, set a good example, like making walking or cycling the norm for short journeys, as recently recommended by NICE (Source). Oh yes, and sit up straight.

Rebecca Reynolds, PhD
University of New South Wales, Australia
rebecca.reynolds@unsw.edu.au

About the author

Rebecca Reynolds is a physical health lecturer at the School of Public Health and Community Medicine, University of New South Wales, Australia. Her background is in obesity prevention at the World Health Organization Collaborating Centre for Obesity Prevention in Geelong, Australia.