"Letting a toddler spend lots of time using screens may delay their development of skills such as language and sociability," BBC News reports.
Researchers followed over 2,000 children in Canada from birth up to the age of 5, with screen time assessments performed from age 2 years onwards.
Screen time was defined as time children spent watching or interacting with any type of screen-based devices, such as tablets, TVs or smartphones.
Overall they found that increased screen time was generally associated with poorer developmental test scores.
However, the study can't prove that screen time is directly responsible for the child's developmental test scores.
A child's development is likely to be influenced by a complex interplay of factors. It is very difficult to pull these factors apart and work out the role of a single factor like screen time.
Recent advice published by the Royal College of Paediatrics and Child Health avoided making specific recommendations on screen time limits, citing a lack of evidence.
But they say that for younger children "face-to-face social interaction is vital to the development of language and other skills, and screen-based interaction is not an effective substitute for this". They also advise "that screens are avoided for an hour before the planned bedtime".
The study was conducted by researchers from the University of Calgary and University of Waterloo in Canada. Funding for the cohort was provided by a grant from the Alberta Innovates Health Solutions Interdisciplinary Team. The study was published in the peer-reviewed medical journal JAMA Pediatrics, and is free to read online.
The UK's media reporting of the study was accurate. BBC News provided some useful additional information about the ongoing debate about screen time recommendations.
This study used data collected from an ongoing cohort study of mothers and children in Canada, to see whether reported screen time was associated with child developmental delay. The authors report that 1 in 4 children show signs of developmental delay, such as communication problems, when they start school.
The main limitation of cohort studies is that they can't prove for certain that too much screen time affects a child's development. A child's development is likely to be influenced by a wide range of factors (confounders).
The All Our Families study recruited over 3,000 pregnant women from Calgary in Canada between 2008 and 2010. They were followed up when their child was aged 4, 12, 24, 36 and 60 months.
Screen time assessments were made at the latter 3 assessments (from 24, 36 and 60 months). Mothers were asked how many hours on typical weekdays and weekends their child used certain devices/media, including watching TV, DVDs, gaming systems and other screen-based devices.
At these ages mothers also completed the Ages and Stages Questionnaire Third Edition (ASQ-3), which is said to be a widely used way to measure screen time. It also assessed development in 5 areas:
In exploring links between the two, various confounding factors were taken into account:
The study analysed 2,441 of the cohort who had completed questionnaires in at least 1 of the 3 follow-up times.
Average (mean) viewing times were 17 hours a week at 24 months; 25 hours at 36 months; and 11 hours at 60 months (5 years).
The statistical model used to analyse screen time against development was complex, but essentially showed that higher screen time was associated with poorer developmental assessments at all assessment points. They also showed, for example, that higher screen time at age 24 months was associated with poorer performance at 36 months. A similar pattern was found for higher screen time at 36 months with poorer development at 60 months.
The researchers conclude that their results support a directional link between screen time and child development. They suggest that "recommendations include encouraging family media plans, as well as managing screen time, to offset the potential consequences of excess use".
This study adds to the growing body of literature exploring the potential effects of too much screen time usage on health and wellbeing.
But by its very nature, this study can't prove that higher screen time definitely impairs development.
The main limitation remains the potential that other factors may be at play. The researchers have made careful attempts to take into account various environmental influences and other factors associated with child upbringing. But it's likely to be a complex mix of hereditary factors, interpersonal relationships, environmental and lifestyle factors that ultimately affect a child's development. It's always going to be difficult to pull apart all of these influences and assess the direct effect of a single exposure such as screen time.
Another thing to consider is that the results only show an overall trend for lower test scores with higher screen time. They don’t actually show that any children have a noticeable "impairment" or were at any disadvantage compared to other children. Despite lower test scores they may function and develop perfectly normally.
The questionnaire is said to be a valid method of assessing media use, but these are still estimates and there may be some inaccuracies.
Finally, this is a very specific population sample from one region of Canada, of mostly white ethnicity and from higher income households. The same results may not be seen in other samples.
The overall message would still seem to be that it's better for children to have a balance and perhaps limited used of screen time combined with other activities like play, reading, interaction with others and physical activity. This advice corresponds to the recent advice for parents provided by the Royal College of Paediatrics and Child Health (PDF, 191kb).