Our results do indicate that the psychological environment of the child may play a role in the development of asthma

Dr David Mrazek

They found that children whose parents struggled to come to terms with the responsibilities of looking after a child were more than twice as likely to develop asthma.

Parenting difficulties included maternal depression, relationship conflicts and a lack of social support.

Asthma is an allergic condition that causes laboured breathing and can be life-threatening.

It is the most common chronic illness of childhood, and the number of cases has risen sharply over the past decade.

Researchers from the National Jewish Medical and Research Center, Mayo Clinic and Colorado Allergy and Asthma Centers studied genetically at-risk children between the ages of six and eight.

They focused on the impact of parenting during the child's first three weeks of life.

Lead researcher Dr Mary Klinnert said: "Asthma is a complex disease with many contributing factors.

"Many of the children in our study with well-adjusted, caring, effective parents still developed asthma.

"But our results do indicate that the psychological environment of the child may play a role in the development of asthma."

Emotions

Of the 150 children studied, 28% had developed asthma by the time they were between six and eight years of age.

Dr David Mrazek, chair of the Mayo Clinic's Department of Psychiatry and Psychology, said that the research emphasised just how powerful human emotions can be.

He said: "This study shows that emotional distress experienced early in life can have long-term health consequences.

"It's important not to blame parents, but to support them in doing their best to provide a nurturing environment."

Dr Mrazek told BBC News Online that it was possible that the stress associated with parental problems caused chemical changes in the body that had an effect on the function of genes thought to be linked to the development of asthma.

Dr Martyn Partridge, chief medical adviser for the National Asthma Campaign, said: "This is an interesting speculative association, which doesn't necessarily imply cause and effect.

"The association may reflect pre-diagnosed symptoms adding to parental stress and more research is needed in this area."

The research is published in the journal Paediatrics.