Mothers who are asthmatic may decrease airflow by breastfeeding their baby, a study suggests.
Theresa Guilbert, from the University of Wisconsin-Madison and the Arizona Respiratory Center at the University of Arizona, noted that breastfed infants whose mums were asthmatic did not have a high lung volume compared to babies whose mothers were not asthmatic.
But in the study, published in the American Journal of Respiratory and Critical Care Medicine, she added it would be "premature" to change breastfeeding recommendations based on one study.
The research could point towards new opportunities for the infant formulation market, which in the UK alone was worth an estimated £329m in 2005. The growth is being led by companies looking to replicate the healthy profile of breast milk.
The subject of breast feeding versus infant formula is a hot topic at the moment and the Food Standards Agency is consulting on proposed changes to UK legislation from the EU, which looks at regulating infant milk advertisements across the bloc.
The Infant Formula and Follow-on Formula (England) Regulations 2007 could be implemented by the end of the year, covering a broad range of points hinged around making sure the nutritional value for any formula satisfies the nutritional requirements of the infant.
Dr Guilbert said: "Longer breastfeeding in infancy is associated with improved lung function in later childhood, with minimal effects on airflow in children of non-asthmatic mothers
"However, longer breastfeeding in children of mother with asthma demonstrates no improved lung growth and significant decrease in airflows later in life."
Dr Guilbert, working with investigators from the Arizona Respiratory Center, analyzed data from the Children's Respiratory Study in Tucson, Arizona, a prospective population based study of 1,246 infants who were enrolled at birth and monitored through adolescence.
Each participant was evaluated for lung function using spirometry. The researchers measured lung volume [forced vital capacity (FVC)] and airflows [forced expiratory volume in one second (FEV1) and FEV1/FVC].
When analyzed as a whole, the group found that FEV1/FVC was lower in breastfed children. However, when the data was analyzed taking maternal allergy and asthma into account, the observed lower airflows associated with longer breastfeeding were only found in those infants with asthmatic or allergic mothers.
Dr Guilbert added: "Breast fed children with non-atopic and non-asthmatic mothers had an increase in lung volume and no decrease in their airflows."
"However, children of mothers with asthma who were breastfed four months or more did not demonstrate any improvement in lung volume. Further, they had a significant reduction in airflows, suggesting that the risk for increased asthma in children of asthmatic mothers may be partly due to altered lung growth."
Dr Guilbert speculates that the breast milk of non-asthmatic mothers may contain certain factors that promote lung development, citing several possible candidates including cytokines, tumour necrosis factor, epithelial growth factor, and prostaglandin.
One cytokine in particular, TGF- â1, is related to elastin production, which is important to normal structure and function of the lungs. The dose of TGF-â1 received by infants via breast milk has been shown to be inversely related to infant wheeze.
"These findings suggest that growth factors in milk have the potential to modify lung development, which might account for some of the protective effect of breastfeeding against wheeze," wrote Dr Guilbert.