Japanese study links breastfeeding to mixed risks for childhood allergies

Breastfeeding is widely recognized for its important role in supporting a child's early growth and immune system development. Previous studies have found that exclusive breastfeeding for 4 to 6 months is associated with a lower risk of bronchial asthma and allergic rhinitis during early childhood. Recognizing these health benefits, the World Health Organization recommends exclusive breastfeeding for the first 6 months of life. Despite its positive effects, its impact on food allergy remains inconclusive.

To address this question, a research team led by Professor Emeritus Hidekuni Inadera, together with doctoral candidate Hitomi Inano, Dr. Kanako Shimada, and Assistant Professor Akiko Tsuchida from the University of Toyama, Japan, examined the association between breastfeeding patterns and allergic diseases using data from a birth cohort of 88,037 mother–infant pairs followed from birth until the children reached 6 years of age. Their findings show that breastfeeding during the first 6 months of life was associated with a lower prevalence of some allergic diseases but a higher prevalence of others. This paper was published in Volume 26 of the journal BMC Pediatrics on April 21, 2026.

"Beneficial associations of breastfeeding were observed for the prevalence of bronchial asthma and allergic rhinoconjunctivitis, while adverse associations were detected for food allergy, particularly in male infants," says Prof. Inadera.

The researchers analyzed data from the Japan Environment and Children's Study (JECS), a large-scale birth cohort that enrolled pregnant women from 15 regions in Japan between January 2011 and March 2014. Participants were divided into four groups based on their feeding pattern during the first 6 months of life: infants who were exclusively formula-fed, breastfed for less than 6 months, breastfed for 6 months while also receiving formula, or exclusively breastfed for 6 months.

The researchers then examined the association between breastfeeding patterns and the development of allergic diseases until the children reached 6 years of age using annual questionnaires completed by caregivers, who reported whether a physician had diagnosed their child with bronchial asthma, allergic rhinoconjunctivitis, food allergy, or atopic dermatitis.

They found that children who were exclusively breastfed for the first 6 months of life were less likely to develop bronchial asthma and allergic rhinoconjunctivitis than children in the other feeding groups. The association with bronchial asthma was strongest during the first 2 years of life and gradually weakened as the children grew older.

In contrast, exclusive breastfeeding for 6 months was also associated with a higher prevalence of food allergy and atopic dermatitis. The association with food allergy was strongest in boys and remained evident until approximately 3 years of age.

The researchers note that one possible explanation for the higher prevalence of food allergy is the timing of complementary food introduction. Previous studies have shown that introducing common food allergens, such as eggs and peanuts, between 4 and 6 months of age may help infants develop immune tolerance, thereby reducing the likelihood of food allergies.

"Consistent with our results and some previous observations, current guidelines recommend that solid food be introduced when infants are between 4 and 6 months while breastfeeding is continued," says Prof. Inadera.

The findings suggest that breastfeeding practices should be considered alongside the timing of complementary food introduction when developing strategies to reduce childhood allergies. Further research is needed to better understand how these factors interact.