The surprising findings run counter to current allergen advice, but experts say it is too soon to change guidelines.
Children whose mothers avoided cow’s milk in pregnancy, and who were not given cow’s milk in the first four months of life, were significantly more likely to develop atopy and asthma by age 23, a longitudinal UK study has found.
The surprising findings could also be due to the soy supplements that some of those children consumed in early life, and experts warn that allergens should still be avoided before four months.
The randomised control trial, which recruited almost 500 subjects between 1982 and 1984, sought to determine whether avoiding cow’s milk in utero and up to four months of age could lower their risk of allergic disease compared with children on a normal diet.
All infants had a parent or sibling with a history of eczema, asthma or hay fever.
Mothers of children in the intervention group were asked to restrict their cow’s milk intake to 284 mL per day during pregnancy and while they breastfed, and a standardised soymilk preparation was offered to babies who were not breastfed.
Mothers were asked not to give any products containing cow’s milk to the child for at least the first 16 weeks of the child’s life.
Pregnant women in the control group had no restrictions on their cow’s milk intake either during or after pregnancy and babies were given a standard cow’s milk-based formula if not breastfed.
Parents, and later subjects, completed standardised questionnaires for allergic disease at age 1, 7, 15 and 23 years, and children were tested multiple times by a clinician for common allergies.
At age 23, almost 300 patients completed the questionnaire and 119 attended the clinical assessment.
More than 40 patients in the cow’s milk exclusion group had been given a cow’s milk product and 32 of those in the normal diet group had soy in the first four months of life.
“The prospectively collected food diaries suggest that earlier exposure to cow’s milk was associated with a decreased risk of wheeze and asthma at age 23 years, while earlier exposure to soya was associated with increased risk of atopy and asthma,” the authors wrote in Thorax.
They acknowledged it was unclear whether the increased risk in the intervention group was due to decreased exposure to cow’s milk or exposure to soy.
However, an independent expert warned the results should be interpreted cautiously and children should not be exposed to foods before four months, as per the Australasian Society of Clinical Immunology and Allergy (ASCIA) guidelines.
The ASCIA guidelines on infant feeding and allergy prevention recommend introducing allergenic foods such as dairy to infants in their first year of life while still breastfeeding, but not before four months.
Paediatric allergy specialist Dr Preeti Joshi, who was not involved in the research, told The Medical Republic the study was not large or rigorous enough to call the guidelines into question.
“The ASCIA guidelines are based on robust data from closely monitored trials and in particular the LEAP study, which is a large, well conducted interventional study with highly significant results,” said Dr Joshi, co-chair of the National Allergy Strategy and ASCIA Council member.
“This [Thorax] paper is interesting because it provides data collected over a long period [but] there are significant limitations to the study … it is open label, had only a 21% response rate at 23 years and, very importantly, there was crossover between intervention groups such that many in the soy group were given cow’s milk and vice versa. Any results must be interpreted with caution.”
Dr Joshi added that ASCIA continued to monitor data emerging from various trials regarding very early introduction of cow’s milk and atopy.
“We are constantly reviewing new data as it comes to light and are vigilant in updating guidelines when the evidence warrants a change,” she said.
Read more: Thorax 2021, 7 May
