Children who have problems in breathing during sleep tend to score lower on tests of mental development and intelligence than do other children their age, according to two studies funded by the National Institutes of Health (NIH). Both studies appear in the October issue of 'Journal of Paediatrics.'

The first study, funded by the National Institute of Child Health and Human Development (NICHD), found that at one year of age, infants who have multiple, brief breathing pauses (apnea) or slow heart rates during sleep scored lower on mental development tests than did other infants of the same age. The second study was funded primarily by the National Heart, Lung, and Blood Institute (NHLBI). Results show that 5-year-old children who had frequent snoring, loud or noisy breathing during sleep, or sleep apneas observed by parents scored lower on intelligence, memory, and other standard cognitive tests than other children their age. They were also more likely to have behavioural problems.

"The findings from these studies support other research that has shown that breathing problems during sleep are associated with serious health consequences in children," said Carl E Hunt, director of the NIH National Centre on Sleep Disorders Research (NCSDR). He added, "However, at this point we don't know if the sleep problems during these episodes cause the decline in test scores or if the sleep episodes and the lower test scores are both related to some common underlying mechanism."

More than 10 per cent of young children have habitual snoring, the mildest form of sleep-disordered breathing (SDB). One to three per cent of children have obstructive sleep apnea, a more severe form of SDB in which breathing stops briefly and repeatedly during sleep. SDB is thought to be more common in toddlers and younger children than in older children because the younger ones are more likely to have large tonsils and adenoids, which can briefly block the airways in the back of the throat during sleep. African American children are twice as likely to develop SDB compared to white children. Children who are overweight or obese are also more likely to develop SDB.

In the first study, researchers evaluated 256 full-term and preterm infants at one year of age with a standardized test that measured physical and mental development. The infants were part of the multi-center Collaborative Home Infant Monitoring Evaluation (CHIME) study. The CHIME study sought to identify factors that could put infants at risk for sudden infant death syndrome (SIDS).

Participants included healthy infants as well as those at increased risk of SIDS because they had a history of prematurity, a life-threatening event during sleep, or a sibling who had died from SIDS. The infants' breathing, heart rates, and blood oxygen levels were monitored electronically at home for the first 4-6 months of age.

The second study involved 205 children at 5 years of age. Researchers at Boston University School of Medicine compared neurocognitive function and behaviour of 61 children with SDB symptoms to 144 children without symptoms. Symptoms of SDB, as reported by parents, included frequent snoring; heavy, loud, or noisy breathing during sleep; or observed apneas during sleep. An overnight sleep test (polysomnogram) was also performed to objectively measure the severity of SDB.

The study found that children with SDB symptoms scored lower on standard tests measuring executive function (attention and planning), memory, and general intelligence. These children also had significantly more behavioural problems than children without SDB symptoms, based on parental survey scores.

"One of the more remarkable findings in this study was that the neurocognitive effects were significant even among the children who had mild symptoms of sleep-disordered breathing but no actual sleep apneas," Daniel Gottlieb, lead author of the study said adding, "Parents need to be aware that their child's snoring could signal serious problems."

The mild SDB symptoms associated primarily with snoring in these children result in frequent arousals and fragmented sleep, leading to poor sleep quality and hence to sleep deprivation. Today's findings are similar to other studies of children and adults that link poor sleep or sleep deprivation to problems with school (or job) performance, difficulties with memory and concentration, increased risk of injuries, and trouble controlling impulses, emotions, and behaviour, especially in children.

"Unfortunately, the effects of poor sleep are often overlooked or misinterpreted in children. Rather than appearing sleepy like adults who are sleep deprived, children may in fact seem to be more active or even hyperactive," comments Hunt.

In addition, other researchers have reported that the effects of SDB appear to have long-term consequences for children. For example, a University of Louisville study found that young children who snored loudly and frequently were more likely to have lower grades in middle school even several years after the breathing problem was treated or resolved.

"These two new studies point to the need for parents and paediatricians to be on the watch for what might appear to be less serious breathing problems in their babies and young children when they sleep," notes Hunt. "If we can identify these children before the effects on mental development have occurred, the challenge then will be to identify possible ways to intervene and prevent any reduced potential for doing their best in school," he added.

The health consequences associated with SDB in children are gaining increasing recognition. In April 2002, the American Academy of Paediatrics established clinical practice guidelines on obstructive sleep apnea in children. The guidelines call for all children to be screened for snoring and for children diagnosed with obstructive sleep apnea to be treated.