Researchers from Finland found that children introduced to certain foods later were more likely to become sensitized to them, increasing their risk of developing full-blown allergies.
The American Academy of Pediatrics and other authorities on child health recommend babies be breastfed exclusively up to six months of age, at which time parents can begin introducing solid food.
But there is evidence that this strategy may increase children's likelihood of developing allergic disease, Dr. Bright Nwaru of the University of Tampere and colleagues note in the journal Pediatrics.
Concerns have also been raised that parents with allergies themselves may wait to introduce solid foods to their infants, which could "mask" the relationship between timing of food introduction and allergies, they point out.
To investigate, the researchers looked at 994 children participating in a study of diabetes prevention. All had been followed since infancy. The average duration of exclusive breastfeeding among the children was less than two months.
At age five, 17 percent had food allergies, while 23 percent were "sensitized" to certain inhaled allergens. Twelve percent were sensitized to cow's milk, 9 percent to eggs, 5 percent to wheat, and 1 percent to fish.
Late introduction of some foods increased the likelihood that a child would be sensitized to that food by the time he or she was five years old, the researchers found, whether or not the child's parents had allergies themselves.
The relationship was strongest for eggs introduced after 10.5 months, oats introduced after five months, and wheat introduced after six months. Late introduction of potatoes (after four months) and fish (after about eight months) increased children's likelihood of developing sensitization to inhaled allergens.
The findings suggest that for children at risk of developing allergies, early introduction of foods may help prevent sensitization from occurring, Nwaru told Reuters Health.
However, he added in an email, "We cannot give any contrary recommendation against the current one by AAP and other health institutions at this point for parents trying to prevent allergies in their child. Rather, the next step may be to test this hypothesis in a randomized clinical trial setting."
Exclusive breastfeeding for six months is still "the optimal form of feeding for the child," Nwaru added, "but it seems not to be helpful in preventing allergies in children."
SOURCE: Pediatrics, January 2010.