Breastfeeding can be quite hard work for a baby
The sheer physical effort involved in breastfeeding may leave babies with stronger lungs well into childhood, researchers suggest.
A study of 10-year-olds on the Isle of Wight by UK and US scientists found much better lung function in those breastfed for at least four months.
The different mechanics and duration of sucking may be partly responsible, they said, in the journal Thorax.
If so, changes to the design of bottles could mimic this effect.
Studies have established that breastfeeding protects babies from respiratory problems early in life, but the relationship with lung power later in childhood is less clear-cut.
A total of 1,456 babies from the Isle of Wight were followed all the way through to their 10th year to test this.
A third of them had been breastfed for at least four months, and on average, these children could blow out more air after taking a deep breath, and could blow it out faster.
This happened regardless of whether their mother was asthmatic or suffered from allergies.
The reason for these benefits was not as obvious, the researchers said.
Other studies have suggested that immune chemicals in breast-milk may have a protective effect against asthma.
However, the scientists from Southampton University and the College of Veterinary Medicine in Michigan State University, said that the changes in lung volume they found were not completely characteristic of an asthmatic response, suggesting that other factors might be at work.
Dr Syed Arshad, from Southampton and the David Hide Asthma and Allergy Research Centre on the Isle of Wight, said that the physical effort needed to extract milk from the breast might be involved.
On average, babies needed to generate three times the sucking power compared to bottle-feeding, and feeding sessions tended to last much longer.
Dr Arshad said: "What they are doing is very similar to the kind of exercises we suggest for pulmonary rehabilitation in older patients.
"I'm not aware of anyone suggesting that this might be the reason before."
The research team has now approached a bottle manufacturer with proposals to create a bottle which mimics the effort needed to breastfeed.
He said that it was now possible to carry out lung function tests on infants, which meant that a trial to see if it made a difference could be concluded within a year.
"No-one can argue that breastfeeding is not the best for a child, but it might be possible to make a bottle for women who are unable to breast-feed."
Dr Elaine Vickers, from Asthma UK, said that the study added to the evidence that breastfeeding has "long-lasting benefits" for children.
She said: "While the results of the study don't focus specifically on asthma, the researchers were able to demonstrate that children breast-fed for four months or longer had better lung function than those who weren't breast-fed at all, or who were breast-fed for less than four months.
"We currently support advice from the Department of Health, which states that where possible, babies should be exclusively breastfed for the first six months of life."