Researchers followed children from seven to 11 years old to see whether the number of hours watching TV, playing on the computer or having a TV in the bedroom influenced the risk of having higher body fat in a couple of years.
It found that, compared to children who didn't have a TV in their bedroom at age seven, children who did had a significantly higher body mass index (BMI) and body fat at the age of 11. The association was higher for girls than boys.
Although this is an interesting study with potentially useful findings, it cannot prove there is a direct connection between using screens and body weight. But it would seem plausible that at least some children who spend a lot of time staring at a screen are not meeting the recommended levels for physical activity.
Almost a fifth of UK children are obese. As the study itself puts it: "Ironically, while our screens have become flatter, our children have become fatter."
Where did the story come from?
The study was carried out by researchers from University College London (UCL) and was funded by a grant from the Economic and Social Research Council. The study was published in the peer-reviewed International Journal of Obesity.
Generally, UK media coverage on this study was accurate.
What kind of research was this?
This was an analysis of data obtained from a large prospective ongoing cohort study: the UK Millennium Cohort Study. This particular analysis aimed to assess long-term associations between television and computer use and body fat in children.
In the UK, out of all screen based media, TV remains the most popular amongst children aged five to 11. Concurrently, the prevalence of obesity in childhood continues to increase.
The researchers wanted to investigate the link between TV use and obesity in children by following children over a period of time – between the ages of seven and 11.
Cohort studies such as this are useful for evaluating potential links between exposure and outcome. However, due to the observational study design it isn't always possible to fully rule out the influence of other confounding factors such as diet and physical activity. Therefore it’s difficult to confirm direct cause and effect between the two variables.
What did the research involve?
The UK Millennium Cohort Study (MCS) has followed the lives of children born between September 2000 and January 2002 in all four countries of the UK.
The dataset is nationally representative of the UK general population and includes children from economically disadvantaged areas and different ethnic minorities.
This analysis specifically looked at the data for 12,556 children (6,353 boys and 6,203 girls) who had been followed from the age of seven until 11. Two outcome variables were assessed: use of screen based media and body fat in children.
Body fat at the age of 11 was measured using three indicators:
- body mass index (BMI)
- fat mass index (FMI) – total fat mass divided by height squared to reveal the amount of fat in the body
- overweight – based on specific International Obesity Task Force (IOTF) criteria
The use of screen-based media was measured in children at age seven. Three indicators were used:
- whether the child had a bedroom TV
- number of hours spent watching TV or DVDs
- number of hours spent playing on the computer
The researchers analysed the data to look for any associations between screen-based media use and body fat in children.
The following confounding factors were adjusted for:
- child age
- child BMI at nine months old and three years old
- breastfeeding duration
- child ethnicity
- maternal BMI
- maternal education
- family income
- bedtime at age seven
- physical activity at age seven
What were the basic results?
At age seven around half of the boys and girls in the sample (55% and 53%, respectively) had a TV in their bedroom. At the age of eleven, 25% of boys and 30% of girls were found to be overweight
Overall in this sample, children who had a TV in their bedroom at age seven had a significantly higher BMI and FMI at the age of eleven compared to those who didn’t.
The association were stronger for girls than boys.
Girls had 0.57 kg/m2 excess BMI (95% Confidence interval [CI] 0.31 to 0.84) and boys 0.29 (95% CI 0.06 to 52).
In relative risk terms this equated to girls with a TV in their room at the age of seven having around a third higher risk of being overweight at age eleven (relative risk [RR] 1.31, 95% CI 1.15 to 1.48) and boys a 21% increased risk (RR 1.21, 95% CI 1.07 to 1.36).
How did the researchers interpret the results?
The researchers concluded: "Our longitudinal analysis has shown that having a TV in the bedroom is an independent risk factor for increased body fatness in this nationally representative sample of UK children.
"Girls who had a TV in their bedroom at age 7 were at an approximately 30% higher risk of being overweight at age 11 compared to those who did not have a TV in their bedroom, and for boys the risk was increased by about 20%."
This analysis used data from the UK Millennium Cohort Study to assess for long-term associations between television and computer use and body fat in children.
It found that compared to children who didn't have a TV in their bedroom at age seven, children who did had a significantly higher BMI and FMI at the age of 11. The association was higher for girls than boys.
This is an interesting study however there are a few points to note:
- Although the researchers tried to adjust for potential confounding factors, including physical activity at age seven, it’s difficult to know that its influence was fully taken into account. An unhealthy diet and lack of physical activity are two of the biggest contributors to obesity. It's quite likely that children who spend a large amount of time in front of screen-based media don't spend quite as much time getting exercise outdoors or through team sports etc. However, without full analysis of diet and level of physical activity of these children, it’s not possible to conclude that media viewing is the direct cause of these findings.
- The difference in BMI was actually relatively small: 0.57 and 0.29 for boys. It’s difficult to know what effect this difference would have in terms of health and long-term outcomes.
- The analysis only looks at viewing age seven and weight outcomes age 11. It would be valuable to look at patterns in other ages and over the longer term.
- The dataset for the MCS represented different ethnicities but in this particular analysis 84.6% of the children were white. Genetics and cultural differences do have an impact on children's behaviours so it would have been interesting to see whether children from different ethnic backgrounds had different results.
Overall this study doesn't prove that watching TV or having a TV in your bedroom directly increases body fat. However, the link between increased sedentary time in general, along with low physical activity and poor diet, and overweight and obesity is quite well established.
Current guidelines recommend children and young people need to do at least 60 minutes of physical activity every day.
Read more about how to help your child get more active.