Poor sleep 'causes ADHD'

“Too little sleep 'can make children hyperactive'” according to The Daily Telegraph. The newspaper says that a new study suggests that a lack of sleep makes it more likely that children will “develop behavioural problems and become hyperactive”.

This study of 280 seven and eight-year-olds from Finland looked at whether how long they slept affected their levels of symptoms of attention deficit hyperactivity disorder (ADHD). It found that children who slept for less than 7.7 hours on average scored higher on tests of hyperactivity and impulsivity than those who slept for longer.

It is important to remember that this study looked only at levels symptoms associated with ADHD, and that it was unclear whether any of the children would actually have been medically considered to have ADHD. Another major limitation was that it measured sleep duration and ADHD symptoms during the same time period and therefore could not determine whether shorter sleep times might cause ADHD symptoms or vice versa. This and other limitations mean a causal link between sleep duration and ADHD symptoms has not been proven by this study.

Where did the story come from?

Dr E Juulia Paavonen and colleagues from the University of Helsinki and other research centres in Finland carried out this research. The study was funded by various organisations including the Academy of Finland, the European Science Foundation and the Finnish Foundation for Pediatric Research. The study was published in the peer-reviewed medical journal Pediatrics.

What kind of scientific study was this?

This was a cross-sectional study on the relationship between sleep duration and levels of behavioural symptoms of attention-deficit/hyperactivity disorder (ADHD) in children.

The participants in the study were recruited from a cohort of 1,049 children born from March to November of 1998 in Helsinki, Finland. In 2006, the researchers invited 413 of these children and their parents to participate in the current study, and 321 agreed.

The researchers excluded children with neurological conditions that might affect sleep or behaviour.

To assess their sleep the children were asked to wear a monitor called an actigraph on their wrist for seven days. Parents were also asked to record when the children went to bed, got up, took off the monitor, and if the children experienced any problems or conditions that might affect sleep during the monitoring period.

The researchers excluded data from any nights when the actigraph was not used, when information about bedtime or other factors was not available, when the parental report of bedtime and the actigraph recordings did not agree, or when the parent reported that the child’s sleep pattern was significantly different from usual (e.g. due to travel or illness).

The children’s parents were given standard questionnaires about the children’s sleep patterns and their levels of symptoms associated with ADHD. This symptom questionnaire measured levels of hyperactivity/impulsivity and inattention, and these scores were added to give a score indicating the overall level of ADHD symptoms, known as the ‘ADHD total symptom score’.

In their final analysis, researchers included 280 children (146 girls and 134 boys with an average age of 8.1 years), who provided complete data. The researchers defined the children as:

• short sleepers, whose sleep duration was in the bottom 10% of recordings (an average of less than 7.7 hours       a night),
• average sleepers (between 7.7 and 9.4 hours a night), or
• long sleepers, whose sleep duration was in the top 10% of recordings (an average of more than 9.4 hours or less    a night).

The researchers used statistical methods to compare behavioural symptoms between these groups of children. Some of their analysis took into account other factors that might affect duration of sleep (potential confounding factors), such as age, sex, parental level of education, height, body mass index, mother’s age, and neurologic and other illnesses such as dyslexia, dysphasia and eczema.

What were the results of the study?

Using data on sleep length collected by the actigraph, the researchers found that children who slept for the least amount of time (less than 7.7 hours a night) scored higher on both the hyperactivity/impulsivity and ADHD total symptom scales when compared with children who slept for longer. There was no difference in inattention score between children who slept less than 7.7 hours a night and those who slept more.

After taking into account all of the potential confounding factors, only the link between shorter sleep and higher hyperactivity/impulsivity symptoms remained significant. When the researchers looked at parent-reported sleep duration rather than actigraph readings, they found no significant association with ADHD symptom scores.

What interpretations did the researchers draw from these results?

The researchers concluded that “short sleep duration and sleeping difficulties increase the risk
for behavioral symptoms of attention-deficit/hyperactivity disorder” in children. They also recommend that intervention studies be performed to confirm the causality.

What does the NHS Knowledge Service make of this study?

The main limitations of this study relate to the difficulties measuring sleep or symptoms of ADHD and in proving that one factor is actually causing the other:

• The study was cross-sectional, which means that both sleep length and ADHD symptoms were measured in the same time period. This means that it is not possible to say whether children’s sleep patterns could have caused their ADHD symptoms, as the study does not show which of these characteristics developed first. It is possible that higher levels of ADHD symptoms lead to children sleeping less, rather than the other way around.
• The study measured levels of ADHD symptoms, not clinical ADHD diagnoses. It was unclear whether any of the children in the study would have been clinically diagnosed as having ADHD.
• Although scores were higher in the short sleepers, it is also unclear whether the differences seen (about two points on the hyperactivity/impulsivity scale) would be large enough to be important to the child or parent.
• The children in this study were generally healthy. Results may not apply to children who are less healthy.
• Actigraphs measure movement rather than sleep (period at rest), therefore these readings may not accurately reflect sleep duration.However, studies have suggested that actigraph readings corresponded well with measurements taken in a sleep laboratory.
• To interpret the actigraph readings, the researchers used the bedtimes reported by parents and inaccuracies in these reports may also have affected results.
• Children’s sleep patterns over the measurement period may not have been representative of their usual sleep duration.
• Many statistical comparisons were carried out in this study and this increases the likelihood that significant results may be found by chance. After full adjustment for all potential confounders, the link between sleep duration and hyperactivity/impulsivity was only just statistically significant (p value of 0.0498). If the researchers had taken into account the multiple comparisons, this value may have become not significant.

Getting a sufficient amount of sleep is important in both children and adults. It will require further studies looking at children’s sleep patterns over time and any subsequent development of diagnosed ADHD in order to determine whether there is a causal link with this disorder.