In this issue of Attention Research Update, I review an interesting study on whether excessive exposure to television in early childhood may contribute to the development of ADHD symptoms later on.  This study has been widely publicized in the media, and some of the reports I have seen appear to oversimplify a complex issue.  Results from this study are important because they highlight the important role that experiential factors may play in the development of ADHD, even though genetic influences are known to be quite important.

Because the study below is about the risks associated with excessive TV viewing, and this is an issue that parents and children often struggle with - at least in my house - I want to let you know about a device that has been very helpful in our family.  It is called the Time Scout, and I have found it to be a terrific way to limit TV viewing without the arguments and without having to carefully monitor how much my daughter has watched.  You can learn about this at http://www.time-scout.com

DOES EARLY TELEVISION EXPOSURE LEAD TO ADHD?

Although prior research has clearly shown that genetic factors are an important contributor to the development of ADHD, most experts agree that genetic factors are not the sole cause of the disorder.  Some researchers have suggested that early childhood experiences also contribute to attention difficulties and other ADHD symptoms, and that that the combination of genetic factors and environmental experiences may be critically important in the development of ADHD, as well as in its severity and progression.

One particular experience that has been suggested to contribute to the development of ADHD symptoms is excessive television viewing, particularly at early ages.  Television is characterized by rapidly changing images and scenes that unfold at a considerably faster pace than events in the real world.  Although this can make TV highly stimulating and attention grabbing, it has been hypothesized that this may reduce children's attention spans for real-world activities that unfold at a slower pace.

There is considerable evidence that children's experience during their early years can influence the development of their central nervous system.  Thus, the types and intensity of early visual and auditory experiences may exert a significant influence on their brain development.  In fact, the American Academy of Pediatrics recommends that parents exercise caution in letting children under age two watch television, in part because of concerns about how this may affect early development of the central nervous system.

The important question of whether excessive television viewing in early childhood contributes to the development of ADHD symptoms was examined in a study published in the April 2004 issue of Pediatrics (Christakis, D., et al. 2004. Early television viewing and subsequent attentional problems in children. Pediatrics, 113, 708-713).  Results from this study are based on over 1200 6-8 year-old children drawn from the National Longitudinal Survey of Youth (NLYS).

This study began in 1979 with a nationally representative sample of over 12,000 14-22 year-olds who were interviewed annually or biennially on a wide range of health related topics.  In 1986, data collection began on the children of the female members of this sample.  In the current study, mothers rated their child's ADHD symptoms at age 7 using items from a standardized behavior rating scales.  These ratings were then examined in relation to information about the child's exposure to television that had been collected during prior waves of the survey, when children were ages 1 and 3.  Thus, the researchers could examine whether children who had watched more TV at 1 and at 3 had higher ADHD symptom ratings when they were 7.

It is important to understand how ADHD symptoms were measured in this study.  This was done by having mothers rate whether each of the following 5 behaviors were either often/sometimes true of their child vs. not true of their child.  The behaviors rated by mothers were:

1) has difficulty concentrating;

2) is easily confused;

3) is impulsive

4) has trouble with obsessions;

5) is restless;

The number of items endorsed as either often or sometimes true was summed and children whose total scores fell in the highest 10% of the sample were classified as having attention problems.  As the authors note, this can certainly not be viewed as equivalent to a confirmed diagnosis of ADHD.  Instead, children with high scores on this scale can be regarded as having characteristics that are frequently seen in children with ADHD.  It should also be noted, however, that 2 of the items on this scale - "is easily confused" and "has trouble with obsessions" - are not directly related to any currently recognized ADHD symptoms  (For a review of ADHD diagnostic criteria, visit

http://www.helpforadd.com/criteria.htm ).

Thus, although it is reasonable to describe children in the top 10% on this scale as demonstrating higher levels of ADHD symptoms than the other children, they should not be regarded as having an actual ADHD diagnosis.

To assess children's exposure to television when they were 1 and 3, mothers were asked how many hours of television their children watched on a typical weekday and a typical weekend day.  These figures were used to compute an average number of hours viewed per day for each child.   It is important to emphasize that these data were not retrospective estimates obtained when children were 7.  Instead, hours of TV viewing were collected during earlier interviews with mothers when their child was both 1 and 3.  This is an important strength of the study, as estimates collected when children were young are likely to be more accurate than if retrospective estimates had been used.

RESULTS

Did children who watched more TV in early childhood show higher levels of ADHD symptoms at age 7?

To address this question, the authors examined whether children scoring in the top 10% on the ratings of ADHD symptoms had watched more TV than children scoring below this cutoff.  In conducting their analysis, the authors controlled for a number of other variables that they felt might be associated with greater ADHD symptoms.  Among the factors they controlled for were gender, ethnicity, child's gestational age at birth, maternal use of alcohol or tobacco during pregnancy, measure of cognitive stimulation and emotional support in the home during early childhood, mothers' education, number of young children in the home, maternal depression, and 1 vs. 2 parent family.  By controlling for these variables, the authors were able to test whether more early television viewing was associated with more ADHD symptoms at age 7, even after differences in ADHD symptoms that might be related to these other factors were taken into account.

The amount of television that children were reported to have watched as 1 and 3-year-olds was quite high: an average of 2.2 hours/day at 1 and 3.6 hours/day at 3.  About 15% were reported to watch more than 5 hours per day when they were 1 and about 15% were reported to watch more than 6.5 hours/day at age 3.  Some mothers reported that their child watched more than 16 hours/day.

Consistent with the authors' prediction, the more TV children had watched the more likely they were to be in the top 10% on ADHD symptom ratings.  Children whose television viewing was in the top 15% of the sample at age 1 - these children watched at least 5 hours/day - were 28% more likely than other children who watched the average amount of TV to be in the high ADHD symptom group at age 7.  This means that rather than having a 10% chance of being in the high ADHD symptom group, these children had about a 13% chance.  The same pattern was found for television viewing at age 3.  Thus, consistent evidence was obtained for a link between high levels of TV viewing in early childhood and high levels of ADHD symptoms in early elementary school.

SUMMARY AND IMPLICATIONS

Results from this study indicate that children with high levels of early television viewing were more likely to have high levels of ADHD behaviors at age 7, even after controlling for a number of other factors that may be associated with attention problems.  This is the first longitudinal study using a large and nationally representative sample to demonstrate such an association and the authors believe that the magnitude of the risk associated with excessive television viewing was large enough to be clinically meaningful.

The authors acknowledge several limitations to their study that must be considered.  First, as discussed above, their measure of ADHD symptoms is not the same as a confirmed diagnosis of ADHD.  In particular, the absence of any information from teachers is an important limitation.  Thus, although results from this study suggest that excessive early TV viewing may lead to higher levels of ADHD-like behaviors, it does not provide a basis for concluding that excessive early television exposure contributes to the actual development of ADHD.

It is also the case that this study cannot prove that it excessive television actually caused the development of ADHD-like behaviors.  Proving such a causal relationship requires a true experiment in which children would be randomly assigned to high vs. low early TV exposure.  Of course, this would not be ethical and could never be done.  By controlling for a number of other variables that might have increased ADHD symptoms, however, the authors did they best they could at eliminating alternative explanations for their findings.  Thus, their results provide strong suggestive evidence that it was excessive early TV viewing that contributed to the development of later ADHD symptoms.  Of course, it would be important to replicate this result in an independent sample, as this would enable one to have greater confidence in the findings.

The authors also note that they collected no data on the content of what children watched.  Some research has indicated that educational programming such as Sesame Street may, in fact, promote attention and reading among school-age children.  Thus, it is not clear whether it is simply the amount of early TV exposure that is problematic, or whether the impact on subsequent attention difficulties also depends on what children are watching.  This would be an important issue to address in subsequent research.

Finally, this study provides no basis for determining whether excessive TV viewing at later ages may also contribute to the development or worsening of ADHD-like behaviors.  The authors' decision to focus on early television viewing was based on research indicating that early experience can alter central nervous system development, and their hypothesis that early TV viewing might alter that development in ways that contributed to attention problems later on.  Whether similar processes might occur at later ages, however, is unknown.  Of course, it is also the case that the authors did not directly examine whether excessive early TV viewing contributed to changes in central nervous system development that they suggest underlies the increased risk for ADHD behaviors.

Regardless of the important questions that remain to be examined in subsequent research, results from this study suggest limiting young children's exposure to TV during the formative years of brain development - which is consistent with recommendations from the American Academy of Pediatrics - may possibly reduce the subsequent risk of attention difficulties and other ADHD-like behaviors.  One hopes that results such as this will encourage researchers to examine whether modification of other kinds of early experience may also have the potential to reduce the risk of children developing such difficulties.  This is an area that has seen very little research, and investigations geared towards examining how ADHD may possibly be prevented could make a significant contribution to public health.

One final but important note.  As I hope is clear in the above discussion, this study does not demonstrate - as has been suggested in some media reports - that television viewing causes ADHD.  Instead, it suggests that excessive TV viewing in early life may be one factor that increases the risk of subsequent difficulties with attention and hyperactivity.  There is thus no basis for parents to blame themselves for the child having ADHD if they let their child watch TV as a toddler, or to feel that by letting their child continue to watch a reasonable amount age-appropriate TV they are making things worse for their child.  Such conclusions would represent - in my opinion - an important misinterpretation of the study's results and create unfortunate and uncecessary difficulties within families.

Thanks again for your ongoing interest in the newsletter. I hope you enjoyed the above article and found it to be useful to you.

Sincerely,

David Rabiner, Ph.D.
Senior Research Scientist
Center for Child and Family Policy
Duke University