Children who were never breastfed had an increased risk of developing asthma symptoms at age 6 compared with those who were, and this was likely due to increased early life respiratory tract infections in children who were never breastfed, a new study found.

Never-breastfed children had an increased risk of late wheezing between the age of 3 to 6 years (odds ratio [OR], 1.69, 95 percent confidence interval [CI], 1.06-2.69; p<0.05) and persistent wheezing from below age 3 until age 6 (OR, 1.44, 95 percent CI, 1.00-2.07; p<0.05) compared with ever-breastfed children. [Pediatr Allergy Immunol 2016;doi:10.1111/pai.12576]

Among breastfed children, a shorter duration of breastfeeding  (<2 months) was associated with early wheezing at age 3 and below (OR, 1.40, 95 percent CI, 1.14-1.73; p<0.01) and asthma at age 6 (OR, 2.19, 95 percent CI, 1.29-3.71; p<0.01) compared with those who have been breastfed for 6 months or longer.

However, the associations between breastfeeding duration and early wheezing or asthma became insignificant after the researchers accounted for lower respiratory tract infections in early childhood.

Furthermore, children who were introduced to food or drinks other than breast milk during the first 4 months of their life had an increased risk of early wheezing (OR, 1.28, 95 percent CI, 1.08-1.53; p<0.01) compared with those who were exclusively breastfed for the first 4 months. Similarly, these associations were attenuated after adjusting for early respiratory tract infections.

“We speculate that children who were never, shorter or less exclusively breastfed more often had respiratory tract infections in early life,” said the researchers, citing antibodies and other secretory factors present in the breast milk which could strengthen the infants’ immune system and hence reduce respiratory infections, as the underlying mechanisms linking breastfeeding and asthma risk.

The population-based prospective cohort study analysed data from 5,675 children in the Netherlands. Questionnaires were used to assess breastfeeding and children’s wheezing patterns from early life until age 6. Asthma at age 6 was determined based on whether the children have been clinically diagnosed with asthma previously and wheezing during the past 1 year.

The self-reported nature of assessment by questionnaires might limit the findings, according to the  authors, who suggested that longitudinal studies including objective measures on respiratory tract infections and inhalant allergies could elucidate the direction of causality, rather than just associations, in the future.