Background

Television Exposure

A systematic review in 2006 reported that young people watched on average 1.8-2.8 hours of TV per day, however 28% watched more than 4 hours and these were more likely to remain in the high viewing category at older ages.(1) Despite the development of various media technologies over the past 10 years, television content remains at the forefront of total media exposure in young people. It is now accessible through live and scheduled broadcasting, 'On Demand', recorded time shifted programming, online content via computers, mobile phones or other portable devices. More recent statistics have shown that television content exposure accounts for a daily average of 4 hours and 39 minutes across all these platforms. (2)

In the UK there are an average of 2.4 televisions per household,(3) which has risen over the last 10 years, with over 96% of homes having access to digital television.(4) In 2002 58% of UK children aged between 4-9 years had a television set in their bedroom, which rose to 79% of those aged 10-15 years old.(5)

Effects of television

Studies have shown that television viewing in adolescence can provide information on safe health practices, encourage social connections and behaviours. However there are concerns about its effects on aggression, sexual behaviour, substance use, self-image, social behaviour, physical health, life satisfaction and academic attainment. It has been recognised that television viewing does not require any special physical or cognitive abilities and does not require coordination with other people, therefore has a low or non-existent entry barrier compared to other leisure activities. It provides entertainment which is seen as an immediate benefit and the immediate costs appear negligible or are not predicted at all. Many of the associated costs do not result immediately, rather they take longer to appear for example the effects on sleep, material aspirations and consequences of a lack of investment in social contacts, education or career.(6)

Much of the knowledge we obtain about the world is indirect, through fictional or true accounts and experiences of others on television rather than our own experiences.(7) It has been suggested through Cultivation theory that messages obtained through television exposure on a frequent basis, whether accurate or not, makes up an individual's knowledge and affects their perceptions and behaviours.(7-9) Children and adolescents are particularly vulnerable to these messages, which can comprise of violence, sexuality, body image distortion, objectification and adverse health messages including alcohol, tobacco and illicit substance use, and it is more difficult for them to discriminate between what they see and reality.(10-13) However, children and adolescents are also able to learn pro-social content from television viewing and then generalise that learning to real-life situation, to produce helping behaviour, friendliness, imagination, racial and ethnic tolerance and respect for elders.(14-16)

A high amount of television viewing also displaces time spent in important developmental activities such as reading, problem-solving, homework, hobbies and interactions with parents, siblings and friends, and shown to be associated with attachment problems, social ability issues and attention issues.(17) In adults, it is suggested that excessive television viewing promotes social isolation and therefore hinders the development of social support networks and coping abilities, affecting mental health of individuals.(18)

Effects on mental health and behaviour

One longitudinal study has shown an association between television exposure in adolescence and increased depressive symptoms in young adulthood.(19) Television was most closely linked to depression compared to other media content such as videocassettes, computer games or radio, however this study did not adjust for physical activity.(19) Depressive symptoms have been associated with increased television viewing in other studies, although data shows that physical activity can be unrelated to depressive symptoms,(20) whereas it has also shown to be a protective factor.(21) In children, one study has shown that a greater amount of television viewing was associated with psychological difficulties irrespective of physical activity or sedentary time.(22)

Adolescents with a television set in their bedroom were shown to have fewer family meals, poorer school performance and had higher screen time exposure.(23) This exposure is negatively associated with health-promoting behaviours such as life appreciation, health responsibility, social support and exercise behaviour(24) and a risk factor for school life dissatisfaction and anxiety.(21) Anxiety and symptoms of psychological trauma has also been seen in children with greater television exposure.(25) A greater percentage of nightmares and separation anxiety was experienced in children witnessing distressing content on television, with 38% of them experiencing an increase in distress symptoms.(26) Several studies have shown that an increase in television viewing and in particular before going to bed affected sleep times, disturbances and sleepiness in children,(10, 27-30) which may contribute to mental and cognitive dysfunction.(31)

It is proposed that unrealistic ideals of attractiveness are transmitted through the media resulting in body dissatisfaction; a study concluded that idealised commercials led to an immediate impact on negative mood and appearance comparison for both sexes, with an increased body dissatisfaction for girls.(32) These recurrent episodes of dissatisfaction may accumulate over time leading to a longer-term body image dissatisfaction.(33) Music videos in particular have a high content of visual and auditory messages and have shown to bring about body dissatisfaction.(12) A meta-analysis by Groesz showed that body image was more strongly negative for female adolescents after viewing slender ideals in the media.(34) Another study showed that those who watched television content about cosmetic surgery wanted to alter their own appearance using the similar methods more than those not exposed to this content.(35)

High levels of television viewing leads to crowding out of activities which have a positive effect on happiness, such as time spent with friends and collegues.(36) In adults, it has been associated higher levels of loneliness, hopelessness, shyness, feelings of failure and guilt, depression and eating disorders; in addition to lower levels of self-esteem, weight satisfaction, perceived attractiveness and life satisfaction.(30,37) Particular television content also appears to directly affect mental health, especially news content which individuals are exposed to frequently,(38) which have shown to intensify depressed moods.(39) Heavy television viewers tended to overestimate crime rates, show more anxiety,(40) have less trust in others,(41,42) overestimate the affluence of others,(43) have higher material aspirations(44) and rate their own relative income lower,(46) leading to a lower subjective well-being.(47)

In adults who are experiencing stress, mood management theory predicts television is used to ameliorate moods or block anxious thoughts.(39,48) Stress is associated with an increase in self-reported television viewing in and adults(48) and in adolescents as a coping strategy.(49) In children, stress has been associated with an increased amount of television viewing in children who usually watched a greater amount of television.(50)

Effects on physical health

Television viewing in children and adolescents has shown to be associated with poor fitness, being overweight, smoking and raised cholesterol in adulthood, thus having long-term adverse effects on health.(51) Those adolescents with a television set in their bedroom undertook less physical activity, and had poorer dietary habits including higher consumption of foods containing sugar on a daily basis while watching television or as a result of advertisements.(23,52) The act of sitting itself had been studied and has been shown to lead to changes in resting glucose levels, blood pressure and biomarkers of cardiovascular disease and cancer.(53)

Anti-social behaviour

It has been shown that media exposure is associated with increased violence and aggressive behaviour, more high-risk behaviours such as substance use and earlier onset of sexual activity.(54) In children as young as three years of age, television exposure has shown an increased tendency to exhibit aggressive behaviour.(25,55) A television violence study has shown that nearly two-thirds of all programmes contained violence, with children's shows containing the most.(56) A longitudinal study found that watching violent television content as a young child was also associated with antisocial behaviour several years later in boys 7-10 years old.(57) One RCT showed that an intervention to reduce television viewing decreased aggressive behaviour in school children, supporting the causal influences of television content on aggression.(58) In adolescents the time spent viewing television content increased the likelihood of subsequent aggressive acts against others.(59) Nearly a quarter of music videos portrayed violence and weapon carrying,(60) and higher alcohol consumption and violent behaviour has been observed in teens from the effect of music videos, particularly from violent lyrics.(61,62) However, studies are not entirely consistent and some show no association between television violence and youth violence and aggression.(63,64)

Aims:

1. To examine the association between amount of television viewing in childhood/adolescence and depression in adolescents.

2. To examine the association between amount of television viewing in childhood/adolescence and antisocial behaviour in adolescents.

Hypotheses:

We hypothesise that adolescents who watched a greater amount of television in childhood or adolescence are more likely to show depressive symptoms and exhibit antisocial behaviour in adolescence. There are likely to be multiple reasons for the association of depression with television viewing including the displacement of time from more important developmental and social activities, certain television content causing distress/anxiety and poor sleep, unreal ideals of attractiveness and life dissatisfaction. Television viewing may also be used to ameliorate mood, block anxious thoughts or as a coping mechanism for stress. Regarding antisocial behaviour, the Cultivation theory predicts that through television content, frequent exposure to messages of violence can affect perceptions and behaviour in children and adolescents.

Exposure and outcome variables:

Exp: Self-reported television viewing at age 16

Out: Depressive symptoms and anti-social behaviour at age 18

Exp: Self-reported television viewing at ages 14 and 16

Out: Depressive symptoms and antisocial behaviour at ages 16 and 18

Exp: Depressive symptoms and antisocial behaviour at ages 14 and 16

Out: Self-reported television viewing at age 16

Exp: Parent-reported television viewing at ages 4, 5, 6, and 9 - Weekday, weekend, school day and holidays to create daily average

Out: Depressive symptoms and antisocial behaviour at ages 14, 16 and 18

Confounding variables:

Physical activity, BMI, previous depression, socio-economic indicators, major life events, substance misuse, gender, maternal depression, completion of school and educational achievement, parental education, neglect, parental abuse, early violence, neighbourhood violence, early antisocial behaviour.

Analysis

The main outcomes could be treated either as a binary or continuous variable. However, both depressive symptom scores and antisocial behaviour do not have normally distributed frequencies so our primary analysis will use logistic regression with binary outcomes. We will use the logistic regression model to adjust for confounding variables.

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