Cases of ear infections have also increased in recent years. Children who regularly develop ear infections may have an increased risk of asthma, a study suggests.

Doctors in the United States examined the medical records of 7,538 children between the ages of two and 11.

They found that children with a history of multiple ear infections were twice as likely to develop asthma compared to those who had never had an infection.

Writing in the journal Chest, they called for more research to see if there really is a link.

As many as 150m people around the world have asthma and the numbers are rising fast. It causes 180,000 deaths each year.

Scientists do not know why so many people are developing the condition. However, a number of theories abound, one of which is that illness in childhood increases the risks.

This latest study suggests that there may be a link with ear infections.

Higher risk

Researchers at the University of Illinois at Chicago found that 72% of the children they looked at had suffered at least one ear infection. Overall, 9% had asthma.

They found that the risks of developing asthma increased with each infection.

Further research is clearly needed

Professor Martyn Partridge,
Asthma UK

Children with three or more infections were twice as likely to have asthma compared to those who had never had an infection.

"The prevalence of ear infections has increased significantly over the years, paralleling the rise in asthma rates," said Kamal Eldeirawi, one of those involved in the study.

"Our study confirms the association between the two conditions, showing that ear infections in early childhood may lead to asthma later in life," he said.

"It is possible that specific viruses or bacteria that cause recurrent ear infections may play a major role in the development of asthma.

"It is also possible that antibiotics that are commonly used to treat ear infections increase the risk of asthma, but more research is needed in this area."

Dr Richard Irwin, president of the American College of Chest Physicians, backed the call for more research.

"Determining the relationship between ear infections and asthma may help to identify or even anticipate health problems in children, while enabling physicians to provide more effective treatments for these conditions," he said.

Further research

Asthma UK's chief medical adviser Professor Martyn Partridge said much more research is needed.

"This is an interesting association but there is too little to suggest that one disease has caused the other.

"If the association is not by chance alone then there is a possibility that greater use of antibiotics is in some way associated with the subsequent asthma," he said.

"The other alternative is that infection of one or other type is associated with the onset of asthma and there have been previous studies suggesting an association between the bacteria mycoplasma pneumoniae and subsequent development of asthma.

"As the authors of this latest study say, further research is clearly needed."