In May 2020 researchers from the USA published their review on the association of extended television viewing with obesity in adolescents. The researchers stated that on a global basis, adolescent obesity is on the rise and is associated with many different serious medical conditions, including some types of cancers, cardiovascular disease, and metabolic disorders. Obesity is the result of many factors including genetics, family history, physical environment, and engaging in activities that result in energy imbalance such as poor dietary habits or lack of physical activity. There is evidence which shows that early development of obesity is a risk factor for obesity in adulthood, therefore early prevention is key in reversing the current obesity epidemic. Recent research has looked at factors which could be modified to reduce the risk of obesity, eg dietary habits, increased physical activity as well as a reduction in sedentary screen-based activities. Screen time and the overall digital environment have gained a great deal of attention as usage rates are on the rise, and screen-based technologies are being developed at a rapid pace. In a recent study of screen time usage rates sampled in 12 countries, children who exceeded screen time guidelines (ie viewing more than 2 hours/day) ranged from 31% in India to 72% in Brazil, with an average of 54% of children not meeting recommendations. In the USA 59% of children, aged 9-11 years, did not meet screen time guidelines, with boys being less likely to meet these recommendations.
A large amount of screen time in children and adolescents has been associated with a number of adverse psychological, behavioural and health factors, including poor self-control, poorer nutritional habits, poorer academic outcome, higher risk of depressive symptoms and social-emotional delay. In addition, earlier onset of screen usage has been associated with reduced mental skills, specifically impulse control, self-control and mental flexibility. A higher amount of screen time has also been associated with poorer physical skills and movement patterns that enabled enjoyable participation in physical activities. In addition, a higher amount of screen time has been associated with higher levels of obesity in children and adolescents, a factor which underlies many other adverse outcomes.
One study found that heavy television viewing on weekend days was associated with a higher BMI three years later, which remained significant after controlling for age, gender, socioeconomic status, sleep duration, eating, exercise, and other screen usage variables, as well as BMI score at the start of the study. The persistence of the association between heavy television viewing and follow-up BMI, indicates that other variables may play a role in the weight of the child, eg organization of the family home, which includes household routines, limits/boundaries, presence of screens in the child’s bedroom, which may lead to less parental screen time monitoring. It has been suggested that excessive screen time at weekends could be replaced by more active pursuits. Although this is a logical strategy for health promotion, simply removing the sedentary screen time may be insufficient as the “displacement theory” has not received convincing support in the literature.
Energy intake appears to be a likely culprit in the rise of adolescent obesity. A review of family-based interventions to reduce screen time has indicated that television exposure was related to changes in energy intake rather than changes in physical activity. A major contributor is the consumption of unhealthy foods while viewing television, as well as the role of food marketing and advertisements in shaping preferences and building brand loyalty for highly calorie dense foods.
A limitation for any study on screen time usage is the rapid pace at which screens are changing in the hands of youth. What constitutes both television and computer usage is constantly shifting, as children use handheld computers to view prerecorded television shows and YouTube clips, many of which include food advertisements. The rapid development of screen-based devices to new formats (eg tablets and smartphones) have impacted screen time among youth and adults based on access and portability of devices, meaning not all screen time is sedentary and the classification of types of screen time is becoming blurred. A new trend in screen usage in adolescents is media multitasking, ie using more than one screen-based device or activity at the same time, which makes measurement accuracy and recall challenging. However, it does seem to be a consistent finding that as children transition to adolescence, there tends to be a sharp increase in screen usage and a reduction in physical activity which increases the risk of the child becoming overweight/obese. The next step is to identify intervention targets and to move from quantifying total screen time to capturing the quality of this screen time. Scientists, public health practitioners, and parents need to better understand the content of screen time, how children use screens to fulfill specific needs, and how their interactions with screens have an impact on their health and choices, not only during screen time but also outside of screen time. It is this that will drive solutions to reduce the risk of obesity for adolescents who are growing up in a screen-saturated environment.
Webster EK, Staiano AE. Extended Heavy Television Viewing May Impact Weight Long Term in Adolescents. J Adolesc Health. 2020 May;66(5):517-519.