Tuesday March 14 2017
Screen time should be balanced out with exercise
"Children who are allowed more than three hours of screentime a day are at greater risk of developing diabetes," The Guardian reports.
In a new study, UK researchers found a link between three hours or more of screen time and risk factors for type 2 diabetes, such as higher body fat.
The study used data from almost 4,500 children aged around 10 years collected between 2004 and 2007. They found that children with more than three hours of screen time per day had higher body fat and insulin resistance compared to children with an hour or less per day. Screen time was defined as time spent watching television and using computers or games consoles.
It is unlikely that the screen time itself is causing an increase in risk; more that this could indicate a more sedentary lifestyle.
One concern is that the data was collected before the use of smartphones and tablets became widespread in children. So it could be the case that screen time use has now increased among children, but we would need further research to confirm this.
Recent US guidelines (there are currently no UK guidelines) recommend no screen time for infants under 18 months, one hour for children aged 2-5, and then older children should be assessed on a case by case basis by their parents.
The study supports current physical activity recommendations for children which say they should do at least an hour's exercise every day. Sticking to this will help reduce the risk of chronic diseases such as type 2 diabetes in later life.
Where did the story come from?
The study was carried out by researchers from the University of London and the University of Glasgow. Funding was provided by the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care (CLAHRC). Data collection was funded by grants from the Wellcome Trust, the British Heart Foundation and the National Prevention Research Initiative.
The study was published in the peer-reviewed medical journal Archives of Disease in Childhood.
There were no conflicts of interest reported by the research team.
The UK media generally reported on this study accurately, though none of the media outlets really explains why this link may have been seen or that the study can't prove that screen time itself increases risk.
The Mail Online provided a number of figures from other sources to add context to the study findings. We are unable to comment on the accuracy of these sources.
What kind of research was this?
This is a cross-sectional survey looking into association between daily screen time and risk markers for type 2 diabetes and cardiovascular disease in children aged nine and 10 years.
Type 2 diabetes and obesity are increasing in adults and children. The effect of sedentary behaviour such as watching television and using computers, known as "screen time", are a cause for concern and associations have been seen between prolonged screen time and body fatness in children.
Using data from this survey the researchers were able to identify potential risk factors, however due to the nature of this study design they would not be able to prove that one thing causes the other. The researchers say they can use their findings to design further studies to prove causation.
A randomised controlled trial would be required to prove such a link. However, a trial that randomises children to different amounts of sedentary time or physical activity and then follows them for sufficient time to observe outcomes may be neither feasible nor ethical.
What did the research involve?
This was a cross-sectional study known as The Child Heart and Health Study in England.
Researchers carried out a survey of primary school children aged nine and 10 years from London, Birmingham and Leicester. A single research team collected key information between October 2004 and February 2007. Some of the information recorded was as follows:
- ethnic origin (based on the ethnicity of both parents)
- socioeconomic status
- skin fold measurements
- fat mass
- blood glucose and insulin levels
- insulin resistance – a measurement of how the body's cells respond to insulin
- blood pressure
- pubertal status measured in girls (girls tend to start puberty earlier than boys)
On the same day as the physical measurements were taken, children completed a questionnaire asking "How many hours each day do you spend watching television or video and playing computer games?"
The children had to tick the most appropriate response, the options were:
- an hour or less
- one to two hours
- two to three hours
- more than three hours
In a sub-group of children, activity was measured using a monitor worn around the waist.
When analysing the findings the researchers attempted to account for the effects of confounding factors such as socioeconomic status, physical activity and pubertal status.
What were the basic results?
The analysis focused on the 4,495 children (2,337 girls and 2,158 boys) who had screen time data, all physical measurements and a fasting blood sample. More than 2,000 children had physical activity data collected from the waist monitor.
The most commonly reported screen time duration was one hour or less (37%), with 18% reporting more than three hours and 4% reporting no screen time at all.
Boys were more likely to have more than three hours of screen time a day, 22% compared to 14% of girls.
Differences were seen between ethnic groups, a higher proportion of black African-Caribbean children (23%) had more than three hours of daily screen time compared with white Europeans (16%) and South Asians (16%).
Children reporting more than three hours of screen time were found to have a higher level of body fat than those with an hour or less screen time.
This was as measured by ponderal index (ponderal means related to weight – the index is a measure of kg/m3; which was on average 1.9% higher), skinfold thickness (4.5% greater), fat mass index (3.3% higher) and leptin (a hormone that controls hunger – 9.2% higher).
They also had higher levels of blood insulin and insulin resistance compared to children taking one hour or less, though there was little link with blood glucose control.
How did the researchers interpret the results?
The researchers conclude: "Strong graded associations between screen time, adiposity and insulin resistance suggest that reducing screen time could facilitate early T2D [type 2 diabetes] prevention. While these observations are of considerable public health interest, evidence from randomised controlled trials is needed to suggest causality."
This cross sectional study aimed to investigate the association between markers for type 2 diabetes and the amount of screen time a child has.
The study found an association between higher levels of screen time and higher body fat and insulin resistance. However, as mentioned, this type of study is not able to prove cause and effect. It is most likely not the screen time itself that is the cause of these factors, more that this could indicate a generally less healthy and more sedentary lifestyle. A similar link might be found for children who spend more time reading books instead of taking physical activity.
The researchers have tried to adjust for physical activity and socioeconomic status that could be influencing the link. However, it is possible that some confounding remains in the model or that other important factors were missed – diet being a notable possibility. It's also possible that children who reported more screen time may have had other health conditions which were not accounted for in the analysis that could have increased their risk.
Other important limitations are that the amount of screen time was self-reported and children may not have remembered or reported this accurately. The measures of body fat and blood glucose control were also one-off measurements taken at single point in time. They don't tell us that the child will go on to develop type 2 diabetes.
Nevertheless the study suggests a reduction in screen time could be beneficial in improving health and possibly reducing the risk of type 2 diabetes and other obesity-related diseases in later life.
One pressing concern is that the data gathered in the study was taken before the use of smartphones and tablets became widespread in older children. Smartphones became commonly used around 2008 to 2010 and the first tablet (the iPad) was released in 2010. So it could well be the case that screen time has now increased in older children.
With these concerns in mind it is important that children are taught to compensate for time spent "gawping at gadgets" (as the Mail puts it) with time spent being physically active.
Guidelines for children and young people recommend that to maintain a basic level of health at least 60 minutes of physical activity every day should be taken; this could be cycling, playground activities or more vigorous activity, such as running and tennis. Exercises for strong muscles and bones are recommended three days a week such as push-ups, jumping and running.
Read more advice about encouraging children to be more physically active.