Obese children often suffer from undetected sleep disorders which could be affecting their performance at school, researchers have warned.
Sleep disorders are linked with being overweight
Researchers from the Royal London Hospital studied 63 children diagnosed as very obese.
They told a British Thoracic Society conference that 54 had a condition called obstructive sleep apnoea (OSA) - a severe form of snoring.
The researchers say all obese children should be checked for the condition.
Most of the OSA cases were mild, but 14 had a moderate or severe form of the condition.
In OSA, airflow is restricted during sleep, leading to a fall in oxygen levels in the blood.
Obesity nearly doubled among youngsters aged two to four between 1989 and 1998 from 5% to 9%.
Amongst children aged six to 15, obesity rates trebled from 5% in 1990 to 16% in 2001.
'Chronic lack' of specialists
One of the Royal London researcher team said: "Obesity and obstructive sleep apnoea is an area which is under studied, particularly among children.
"Awareness of OSA is limited and often undiagnosed.
"Left untreated, these children may suffer daytime sleepiness resulting in poor concentration and leading to poor performance at school."
He added: "Currently, resources in district general hospitals are insufficient to diagnose and treat obstructive sleep apnoea but we need to be able to establish the best way to investigate and treat obese children with OSA if they can't lose weight, which many can't."
Melissa Hack, of the British Thoracic Society, said: "Sleep apnoea is a debilitating condition and left undiagnosed this can seriously affect the day-to-day lives of children.
"There is a chronic lack of lung specialists and 'diagnostic sleep centres' in the UK, which is hampering fast referrals for diagnosis and treatment.
"As a first step to tackling this problem we strongly urge the Government to carry out a national review of sleep services in the UK."
Figures published by the Liberal Democrats also showed that the number of children receiving hospital treatment for obesity-related sleep apnoea had increased 15-fold since 1997.
Data presented in response to a parliamentary question showed that in 1997/98 there were just three cases of paediatric treatment for the condition in England.
But in 2002/03, 48 youngsters received hospital treatment for sleep apnoea.
Liberal Democrat health spokesman Paul Burstow said the rise was "deeply worrying".
"Cases of children with obesity related sleep apnoea are on the rise but treatment for the condition on the NHS is patchy.
"The solution is to tackle the causes of the disease, and combat childhood obesity."
Dr Ian Campbell, chief executive of the National Obesity Forum, said: "Sleep apnoea is a disease that often goes undiagnosed.
"This reminder that it affects overweight and obese children is concerning."
He added: "Children who are overweight or obese have a hard enough time at school.
"But if they are unable to perform to their maximum potential, it is worrying for their future, not just for their health, but also for their social and educational achievements."