Giving newborns cow’s milk formula in the first few days after birth doubles their risk of developing cow’s milk allergy by their second birthday, a small Japanese study suggests.

The authors say the findings of their randomised controlled trial indicate that dairy allergies are “primarily preventable” by avoiding supplementing newborns with cow’s milk formula for at least the first three days of life.

The research randomised 312 newborns born to women at Tokyo’s Jikei University teaching hospital to either an intervention group, where breastfeeding mothers were only allowed to use an amino acid-based elemental formula as a supplement in the first three days, or a usual care group, where they could use cow’s milk formula as a supplement immediately.

Women in the intervention group were allowed to use cow’s milk formula as a supplement after the fourth day of life.