This article summarizes recent findings about associations between electronic screen media and childhood overweight/obesity, hypothesized mechanisms, and mediators. Recommendations are made for parents and clinicians.
Screen time and pediatric overweight/obesity: current knowledge
Over the past 25 years, cross-sectional epidemiologic studies have demonstrated a significant and consistent relationship between time spent watching television (TV) and risk of childhood overweight/obesity. A 2008 meta-analysis of exposure to screen media and weight status found a dose-response relationship with the prevalence of overweight/obesity with increasing longer average screen-viewing durations, quantifying this relationship as equivalent to taking in an extra 100 calories per hour of TV watched. Prospective studies have shown that TV viewing is a risk factor for subsequent weight gain, and a randomized controlled trial has demonstrated that body mass index (BMI, calculated as the weight in kilograms divided by height in meters squared) can be reduced by decreasing TV viewing. Although the relationship between screen time and overweight/obesity was first described in the United States, it has been found around the world. However, the relationship is not always as robust nor as reliable in other countries, suggesting that there may be factors that make TV viewing more “fattening” in certain cultures than in others.
A screen-rich environment
Several studies examining the effects of media on childhood weight status have investigated TV as the primary medium of concern and measured screen time, the duration of TV viewing, as the key independent variable. TV was the first widely used electronic screen medium and is still the medium used for the greatest number of hours by most American children, so the effects of TV screen time have been the longest and best studied. However, the past decade has seen the development of a wide variety of screen media technologies that are used to communicate a plethora of messages in many different ways. Because media devices have evolved, researchers have become increasingly interested in the relationships between uses of emerging media types and childhood overweight/obesity. Studies of relationships between video games and overweight/obesity have provided an opportunity to examine the pros and cons of screen time with different content, compare more active engagement with and contexts of using screen media, and investigate how the effects of exposure to different content can interact with childhood overweight/obesity. For example, a 2009 study on video game use found that the length of game play time in a single sitting, frequency of video game playing, and years of video game playing were each correlated with less exercise and higher BMI, which was consistent with previous findings about the relationship between video game use and childhood overweight/obesity. However, these results are not always consistent, with some studies finding no relationship between video game play and increased BMI. The 2008 meta-analysis of screen time and overweight found that there was no relationship between video game use and BMI but that video game use nevertheless was associated with an increased energy intake, equivalent to 92 calories per hour played, that exceeded energy output. Other research shows that the type of game played is much more predictive than exposure to video games per se. Exergames, interactive video games that require players to be highly active during game play, have very different content and elicit very different metabolic processes than passive games. Exergames have been proposed as a potential alternative to reducing screen time for increasing children’s physical activity. Several studies have shown that exergaming can increase metabolic rate and expend more energy than watching TV or playing a hand-controlled video game but still falls short of the energy expenditure required to actually play the sports that exergaming emulate.
Associations between computer screen time and childhood overweight/obesity have been found but are neither as robust nor as consistent as TV screen time. Similar to TV, computers target children with advertising, both through banner advertisements on child-oriented sites and through dedicated Web sites offering advergaming, engaging electronic games branded for sugared cereals, candy, or other calorie-dense nutrition-poor foods. Uniquely, computer capabilities of operating multiple programs in separate windows simultaneously make media multitasking with a single device not only possible but also a routine for young people, who can simultaneously do homework, download music, interact via social media, play games, surf the web, and use traditional media such as listening to music and watching TV programs. For the most part, researchers are yet to catch up with the capabilities of computers. When investigating computer use, children are very rarely asked about the actual activities in which they are engaged while using the computer and are only asked about the total hours of computer use. It is likely that the reason results vary among studies of computer screen time and overweight/obesity because the content and activities to which one child is exposed can differ dramatically from the exposures of another child with the same cumulative computer screen time.
Because smartphone technology is evolving rapidly and can be used for a variety of different tasks, there is little research so far on associations between cell phone screen time and overweight or obesity. One study linked cell phone use to poor sleep habits, an established risk factor for childhood overweight/obesity. Another study found that playing electronic games, but no other activities, on cell phones was associated with increased BMI, demonstrating that, as with other screens, the content to which users are exposed is heterogeneous and of variable risk for overweight/obesity. Most of the research on cell phones and overweight/obesity has been focused on developing interventions, such as using cell phone gaming or social networking to reduce BMI.
Current research on screen media is indicating that as technology evolves and media content converges, device-based research is becoming increasingly obsolete. Mixed research findings, particularly on devices such as computers and cell phones, which can present a variety of content and formats, emphasize the need to measure contexts of use and exposure to content, rather than simply estimating the time one is in front of specific types of electronic screens. As screen media technologies emerge and new applications are developed, with programming and advertising becoming available on cell phones, computers, video games, and even uninvestigated screens such as global positioning system devices, it is increasingly clear that screens are most important as delivery mechanisms for content. Caloric intake, activity levels, and eating behaviors have been found to vary across content used and the ways in which that content is used. It is not the duration of exposure to screen media that increases risk but the nature of exposure. It is how one uses screen media, the content to which one is exposed, and the contexts in which those exposures occur that drive the relationships between screen media and overweight/obesity. As an example of context rather than duration being critical to overweight/obesity outcomes, children who have TVs in their bedroom are more likely to be overweight than those who watch the same amount of TV but do not have a set in their bedroom. Investigating the mechanisms underlying relationships between screen time and childhood overweight/obesity is critical to understanding and responding to risk in a constantly changing media environment.
A screen-rich environment
Several studies examining the effects of media on childhood weight status have investigated TV as the primary medium of concern and measured screen time, the duration of TV viewing, as the key independent variable. TV was the first widely used electronic screen medium and is still the medium used for the greatest number of hours by most American children, so the effects of TV screen time have been the longest and best studied. However, the past decade has seen the development of a wide variety of screen media technologies that are used to communicate a plethora of messages in many different ways. Because media devices have evolved, researchers have become increasingly interested in the relationships between uses of emerging media types and childhood overweight/obesity. Studies of relationships between video games and overweight/obesity have provided an opportunity to examine the pros and cons of screen time with different content, compare more active engagement with and contexts of using screen media, and investigate how the effects of exposure to different content can interact with childhood overweight/obesity. For example, a 2009 study on video game use found that the length of game play time in a single sitting, frequency of video game playing, and years of video game playing were each correlated with less exercise and higher BMI, which was consistent with previous findings about the relationship between video game use and childhood overweight/obesity. However, these results are not always consistent, with some studies finding no relationship between video game play and increased BMI. The 2008 meta-analysis of screen time and overweight found that there was no relationship between video game use and BMI but that video game use nevertheless was associated with an increased energy intake, equivalent to 92 calories per hour played, that exceeded energy output. Other research shows that the type of game played is much more predictive than exposure to video games per se. Exergames, interactive video games that require players to be highly active during game play, have very different content and elicit very different metabolic processes than passive games. Exergames have been proposed as a potential alternative to reducing screen time for increasing children’s physical activity. Several studies have shown that exergaming can increase metabolic rate and expend more energy than watching TV or playing a hand-controlled video game but still falls short of the energy expenditure required to actually play the sports that exergaming emulate.
Associations between computer screen time and childhood overweight/obesity have been found but are neither as robust nor as consistent as TV screen time. Similar to TV, computers target children with advertising, both through banner advertisements on child-oriented sites and through dedicated Web sites offering advergaming, engaging electronic games branded for sugared cereals, candy, or other calorie-dense nutrition-poor foods. Uniquely, computer capabilities of operating multiple programs in separate windows simultaneously make media multitasking with a single device not only possible but also a routine for young people, who can simultaneously do homework, download music, interact via social media, play games, surf the web, and use traditional media such as listening to music and watching TV programs. For the most part, researchers are yet to catch up with the capabilities of computers. When investigating computer use, children are very rarely asked about the actual activities in which they are engaged while using the computer and are only asked about the total hours of computer use. It is likely that the reason results vary among studies of computer screen time and overweight/obesity because the content and activities to which one child is exposed can differ dramatically from the exposures of another child with the same cumulative computer screen time.
Because smartphone technology is evolving rapidly and can be used for a variety of different tasks, there is little research so far on associations between cell phone screen time and overweight or obesity. One study linked cell phone use to poor sleep habits, an established risk factor for childhood overweight/obesity. Another study found that playing electronic games, but no other activities, on cell phones was associated with increased BMI, demonstrating that, as with other screens, the content to which users are exposed is heterogeneous and of variable risk for overweight/obesity. Most of the research on cell phones and overweight/obesity has been focused on developing interventions, such as using cell phone gaming or social networking to reduce BMI.
Current research on screen media is indicating that as technology evolves and media content converges, device-based research is becoming increasingly obsolete. Mixed research findings, particularly on devices such as computers and cell phones, which can present a variety of content and formats, emphasize the need to measure contexts of use and exposure to content, rather than simply estimating the time one is in front of specific types of electronic screens. As screen media technologies emerge and new applications are developed, with programming and advertising becoming available on cell phones, computers, video games, and even uninvestigated screens such as global positioning system devices, it is increasingly clear that screens are most important as delivery mechanisms for content. Caloric intake, activity levels, and eating behaviors have been found to vary across content used and the ways in which that content is used. It is not the duration of exposure to screen media that increases risk but the nature of exposure. It is how one uses screen media, the content to which one is exposed, and the contexts in which those exposures occur that drive the relationships between screen media and overweight/obesity. As an example of context rather than duration being critical to overweight/obesity outcomes, children who have TVs in their bedroom are more likely to be overweight than those who watch the same amount of TV but do not have a set in their bedroom. Investigating the mechanisms underlying relationships between screen time and childhood overweight/obesity is critical to understanding and responding to risk in a constantly changing media environment.
Proposed mechanisms
Although the significant dose-response relationship between TV screen time and childhood overweight/obesity has been demonstrated at a population level, associations are less consistent with other electronic screen media use or at an individual level. For exposure to electronic screen media to be a risk factor for overweight/obesity, effects of screen-viewing experience on human physiology, of screen content on human psychology, or of screen use contexts on human behavior must create conditions in which the child’s energy intake exceeds energy expenditure. For screen time to increase risk of overweight/obesity, evidence must indicate that features of screen media use contribute to decreased activity, increased consumption, or both.
Decreased Energy Expenditure
Because it seems as if the only time that children sit still is when they are in front of a screen, the first and most extensively investigated proposed mechanism for screen time’s promoting overweight/obesity is decreased energy expenditure due to the sedentary nature of screen viewing. Findings of one early study indicated that basal metabolic rate might be lower while watching TV than during rest or even sleep, suggesting that TV uniquely slowed human metabolism. Although this mechanism has face validity for anyone who has spent too many sedentary hours in front of a TV, none of the several follow-up studies have been able to replicate the original findings; energy expenditure while watching TV was found to be 18% higher than during rest, similar to that of other sedentary activities.
Although energy expenditure while watching TV is not less than when resting, it is less than when engaged in strenuous physical activity. The most commonly accepted mechanism, that sedentary screen time displaces strenuous physical activity, is based on the assumption that if children were not watching TV, they would be running around and playing outside. However, studies have shown that this assumption is not accurate; children whose TV watching is curtailed replace it with other sedentary behaviors rather than strenuous physical activities. Although they are not more active, the weight status of children does improve. Research into communication media, such as texting and social networking Web sites, has shown that children are as sedentary when using these media as when they are watching TV, despite media devices becoming increasingly mobile.
Neither screen time nor other sedentary behaviors have a clear relationship with physical activity. Research has demonstrated that, when comparing people who viewed TV for a long time with those who viewed for a short time, there is no significant difference in physical activity. Other sedentary behaviors, such as reading, have been associated with higher levels of physical activity among children; others had no relationship with weight status at all. This lack of supportive evidence for sedentary behavior as the mechanism of increased risk for overweight/obesity has also been demonstrated indirectly through inconclusive research on screen time using video games, computers, and other media platforms. A methodological problem with some of the studies that have linked screen time and overweight/obesity is that they use screen time (usually TV, sometimes computer use as well) as a proxy for sedentary behavior without examining other types of inactivity. Using screen time as an independent variable does not demonstrate that sedentary behavior is the mechanism of action but simply reaffirms the relationship between exposure to screen and childhood overweight/obesity.
Increased Consumption of Calories
Research has also examined whether watching TV and using other screen media influence children to eat more or eat differently than they might without screen media use. Increased screen time has been associated with more energy-rich nutrition-poor diets in children. The relationship between obesogenic diets and screen media has been explained by 2 different, but complementary, pathways: eating while watching TV and exposure to food advertising.
Eating in front of a screen
A systematic review has shown increased consumption of snack foods, sugar-sweetened beverages, and food that lacks proper nutrients while watching TV and decreased consumption of fruits and vegetables with increases in TV viewing. Children have been found to snack more in proportion to how much TV they watch. A 2004 randomized controlled trial investigated whether eating habits while watching TV varied from eating habits while listening to a book on tape or with no media use. Researchers found that people who ate while watching TV or listening to a recorded story ate larger meals but did not report more satiety, more palatable food, or reduced feelings of hunger compared with eating without any stimulus. Laboratory research found that participants ate more while watching TV than in the absence of a TV screen. A 2005 study in which obese adolescents were given camcorders to document their day-to-day experiences revealed what investigators termed unconscious eating when eating in front of a screen. Children consumed “high-sensation” foods and salt-, sugar-, and fat-containing choices that stimulated their taste buds because their eyes and ears were stimulated by the media they were using. Children took whole bags of snacks, containers of ice cream, or serving bowls of pasta and ate until the containers were empty, completely focused on screens. These observations, coupled with laboratory findings on consumption and auditory/visual stimulation, showed that eating while in the presence of an engaging stimulus such as screen media may lead to a disconnect from physiologic cues of hunger and satiety, leading to unconscious consumption of supraphysiologic calories.
These results are consistent with other research showing that children’s eating while watching TV is more affected by different types of screen stimuli than by hunger. A recent study on computer use found that when children were distracted by a computer game, they ate more and felt less full after eating than children who did not play a game. Although children have shown signs of unconscious eating in controlled trials involving video games, the type of game played affected this behavior. In one trial of game play, boys ate more while playing only fighting games but not puzzle games, and girls ate less when playing video games than when just sitting around in a control environment. Children do not eat consistently in front of every screen type, and the results of comparable studies have not been consistent from country to country, which provides further evidence that sedentary behavior is not the only, or even the predominant, mechanism by which screen time promotes overweight/obesity but that the contexts of media use and content of the media used may be more important than the duration of use.
Food advertising and product placement
Food is advertised very aggressively to children, despite the fact that children themselves do not actually make household food purchases. The food advertised is most frequently energy-dense nutrition-poor sugared cereals, snack foods, and candy. TV advertising directed toward children is very effective. Children exposed to advertising show clear preferences for the advertised foods and choose branded food products over identical but nonbranded products whether or not it is a known or recognizable brand. Parents want their children to eat better and often buy food items that children request so that they will eat something; thus food sales often parallel effective commercial campaigns. In young children, even an exposure as short as 30 seconds has been shown to significantly influence food preferences. Food advertisements, when compared with advertisements for nonfood produces, have an immediate effect, increasing food consumption at the time of exposure, and there is some evidence that the unconscious eating in front of the screen may be motivated by advertising.
Advertising is ubiquitous on TV and Internet. Successful advertising requires only brief exposure and a low level of comprehension to be effective. One study found that even when viewers fast-forward through advertisements on digital video recorders (DVRs), they absorb advertising messages as if they were watching them at their normal speed. Children younger than about 7 years do not yet have the neurodevelopment to discern persuasive intent ; often they do not perceive any difference between programming and commercials, viewing advertising for candy from the same perspective as a lesson about dinosaurs: more information about something interesting. However, even a child who is media literate, able to deconstruct the persuasive messages of advertising, is not immunized against finding advertised food products desirable. Obese children have proven to be better able to recognize food cues in advertising than nonobese children, suggesting that increased education and heightened awareness about food advertising is not an effective technique for decreasing the impact of advertising on food consumption among children. Increasing children’s media literacy and ability to discern persuasive intent has been shown not to protect them against advertising influence but may actually have a boomerang effect in which they believe that if advertisers have gone through so much trouble and expense to let them know about a product, it must be really good (Chervin A. The relationship between children’s knowledge of persuasive intent and persuasion: the case of televised food marketing. Unpublished doctoral dissertation, University of Pennsylvania. 2007: Paper AAI3292015).
Content analyses of food advertising consistently show that the food advertised on TV, in some research, specifically food advertisements directed toward children, is unhealthy, often high in sugar and fat, and does not represent the necessary parts of a balanced diet, such as sufficient amounts of fruits and vegetables. The amount of food advertising on TV has been highly correlated with rates of childhood overweight/obesity in international comparisons. Advertising is so highly related to overweight/obesity so that 1 analysis predicted that, had their exposure to TV advertising been limited, as many as 1 in 3 obese children in the United States would have a healthy weight.
Because commercials are often skipped by leaving the room or fast-forwarding a DVR, an increasingly prevalent variation on food advertising is product placement, the insertion of specific products or advertising for those products into the programming itself. Although the Federal Communications Commission has set limitations on the amount of advertising that can occur during breaks in children’s TV programming, it does not have any restrictions for advertising products within program content or any restrictions for advertising on primetime TV, which many children watch. A review of the most-watched TV shows in 2005 found that product placement is extremely common; in 2005, the number 1 show American Idol had more than 3000 counts of product placement. Product placement is also common in movies, with nearly 70% of the movies in the box office top 20 from 1996 to 2005 containing product placement for food, beverage, or food retail establishments. The Internet was built on commerce, with products being featured and sold on many sites, banner advertisements for products supporting even unrelated Web sites, and products deeply embedded in the content of seemingly noncommercial sites. The most overt example of this is the relatively recent phenomenon of advergaming. Cereal, candy, and other companies have created Web destinations for children, which feature engaging games that are branded with the company’s products and logos, offer discounts or other deals, and provide the opportunity for young consumers to share these games with their friends. However, to date there is little research on the effects of advergaming and product placement on eating behaviors and weight outcomes in children.
What distinguishes food advertising and product placement from other possible mechanisms influencing childhood overweight/obesity is that the hypothesized obesogenic effects are driven by exposure to screen content rather than energy imbalance while using screen media . Screen media content, in the forms of food advertising and product placement, has been shown to be a robust predictor of BMI. Longitudinal research has shown that educational programming, with no commercials, does not have the positive relationship with childhood overweight/obesity that commercial programming has. Distinctly different relationships between screen time and childhood overweight/obesity observed in different countries may be the result of different regulations and practices regarding broadcast of food advertising and product placement.
Environmental and cultural moderators
Childhood overweight and obesity, an epidemic in the United States and other developed countries, is clearly multifactorial in origin and varies among individuals and across cultures, developing and continuing because of an array of lifestyle expectations and choices (of which screen media use is one). To date, there have been no studies investigating the relative contributions of different mechanisms by which exposure to screen media may influence risk of overweight/obesity. Empirically, it is most likely that there are multiple mechanisms by which screen media use affects risk of overweight or obesity in each individual. Sedentary screen-viewing behavior combined with exposure to obesogenic content and unconscious eating may cumulatively contribute to overweight/obesity in individuals or groups for whom each mechanism alone may not predict risk. Although the dose-response relationship between TV viewing and childhood overweight/obesity has been consistently demonstrated at the population level, insufficient power of each mechanism combined with individual and cultural moderators may explain variations among individuals and subgroups.
Relationships between screen time and childhood overweight/obesity vary around the world, modified by socioeconomic status (SES), local broadcast standards, and cultural customs of media use, eating, and activity. A 2003 study in China, in which household TV was not common before 1997, children’s screen time was about one-fourth of that of American children, and statutory guidelines regulate advertising to children, failed to find any significant relationship between screen time and weight status. Subgroups within countries can also show variation; a 2009 multivariate analysis of health behaviors among children in US racial and ethnic subgroups found screen time not to be related to overweight/obesity among black and Hispanic children, suggesting that reducing screen time among these subgroups does not affect their weight status. A recent study showed that although Hispanic and black adolescent women had significantly higher BMIs than their white counterparts, a relationship between TV screen time and BMI was found only among whites.
Within-group differences can sometimes be attributed to factors such as family environment or SES. Eating dinner routinely with one’s family has been shown to be a protective moderator between overall exposure to screen media and childhood overweight/obesity ; eating family meals while the TV is on erases this protective effect. An Australian study associated children’s weight and screen time with their mothers’ employment status; children of mothers who worked part-time watched less TV and were not as overweight as those whose mothers worked full-time or were unemployed, indicating nonlinear modification by lifestyle or SES of the screen time–overweight/obesity relationship. Children whose parents perceived their neighborhoods to be unsafe played outside less, watched TV more, and had higher BMIs. Because lower SES predicts both perception of neighborhood safety and length of parental work days, it seems to be an important moderator of the findings that children of families with low SES watch more TV and have higher BMIs.
Children who have TVs in their bedrooms have been consistently found at greater risk for overweight/obesity than those who do not, an association that led one Centers for Disease Control and Prevention expert panel to make removing TVs from bedrooms a leading recommendation for combating childhood overweight/obesity. Children with TVs in their bedroom watch more TV overall, and their viewing is less supervised; so they are likely exposed to greater amounts of food advertising and product placement as well as content that might contribute to nightmares or other sleep disturbance. A randomized controlled trial has shown that both evening TV viewing and exposure to violent programming disrupt children’s sleep patterns but nonviolent daytime TV does not. Sleep may be an important moderator of the screen media–overweight/obesity relationship. TV viewing has repeatedly been associated with getting less or poorer-quality sleep, and getting sufficient sleep has been associated with healthier weight. A longitudinal study of young children who were controlled for initial BMI and a variety of sociodemographic risk factors (but not screen media) found a dose-response relationship between hours of sleep and risk of overweight/obesity, with each additional hour of sleep per night coming to an associated 0.56 decrease in BMI. Another study found that preschool children who had screen media limits, got adequate sleep, and ate meals as a family had approximately 40% lower risk of obesity than those who had none of these routines.
Because individuals filter media messages through their own experiences and perspectives, children’s gender can influence the effects of exposure to screen media on their risk of overweight/obesity. However, in the limited research that has been stratified by gender, the direction of gender-specific influences is mixed. Among US high school students, boys and girls who watched TV for less than 1 h/d had no increased risk of overweight/obesity, and boys only had increased risk when they watched more than 4 h/d combined with low levels of moderate physical activity. For girls, moderate physical activity for 3 to 5 d/wk combined with less than 1 h/d TV viewing seemed to be protective, but more than 4 h/d TV viewing increased risk of overweight/obesity in an inverse dose-response relationship to their level of physical activity. Similarly, a study in France found screen time to be associated with overweight among girls but not among boys. Conversely, a US study found that a TV in a child’s bedroom, often used as a proxy for increased screen time, was associated with overweight among boys but not girls.
Because of cultural ideals and gender-related expectations, exposure to food-related screen media content can affect girls in different ways than it affects boys. When 8- to 12-year-old boys and girls watched movies with food commercials or nonfood commercials, boys who watched food commercials ate more than those who watched nonfood commercials, but girls who watched food commercials ate less than those who watched nonfood commercials. A Dutch study of emotional eaters found that boys snacked while watching TV, whereas girls did not. Screen media, even for young children, have portrayed and promoted a thin body ideal for women that can become internalized and lead to girls’ dissatisfaction with their bodies and subsequent weight loss behaviors. The difference between how TV sitcoms criticize overweight female characters and have fun with overweight male characters is one example of how different media portrayals may contribute to different eating habits between the genders. Although gender clearly plays a moderating role in how children receive and respond to media messages, the directions of children’s weight-related responses and mechanism of influence require more extensive research to clarify.
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