Children who snore, or who have other night-time breathing conditions, are at risk from behavioural problems, according to a study.Sleep apnoea and snoring made conditions such as hyperactivity more likely later on, researchers said.The study, published in the US journal Pediatrics, looked at data on 11,000 children living in the UK.Lead researcher Dr Karen Bonuck said the sleep problems could be harming the developing brain.One estimate suggests one in 10 children regularly snores and 2% to 4% suffer from sleep apnoea, which means the breathing is obstructed and interrupted during sleep.Often enlarged tonsils or adenoids are to blame for the conditions.In adults, the result can be severe day-time tiredness, and some studies have hinted that behavioural problems such as attention-deficit hyperactivity disorder might be linked to the condition in children.The latest study is sufficiently large to offer a clearer view of this.Oxygen supplyParents were asked to fill in a questionnaire in which both the level of snoring and apnoea were recorded in the first six or seven years of life, and contrasted with their own assessment of the child's behaviour.Dr Bonuck, from the Albert Einstein College of Medicine at Yeshiva University in New York, said that children with breathing issues during sleep were between 40% and 100% more likely to develop "neurobehavioural problems" by the age of seven.She believes that the sleep breathing issues could cause behavioural problems in a number of ways - by reducing the supply of oxygen to the brain, interrupting the "restorative processes" of sleep or disrupting the balance of brain chemicals.She said: "Until now, we really didn't have strong evidence that sleep-disordered breathing actually preceded problematic behaviour such as hyperactivity."But this study shows clearly that symptoms do precede behavioural problems and strongly suggests that they are causing these problems."Marianne Davey, from the British Snoring and Sleep Apnoea Society, said that sleep problems in the young were an under-recognised reason for poor behaviour.She said: "Often parents won't make the connection and mention them to the GP, so this label of ADHD is given to the child, and sometimes they are even given drugs."This is wrong, as if the sleep problem is addressed, the behaviour will improve almost immediately."