The results, based on more than 7,000 children in the Netherlands, support one theory that early exposure to certain fatty acids in fish protects against the development of asthma, said lead author Jessica Kiefte-de Jong, at the Erasmus Medical Center in Rotterdam.
"Introduction of fish between 6 and 12 months but not fish consumption afterward is associated with a lower prevalence of wheezing," she and her colleagues wrote in Pediatrics.
"A window of exposure between the age of 6 and 12 months might exist in which fish might be associated with a reduced risk of asthma."
Concern over seafood allergies prompts some parents and doctors to delay introducing fish into babies' diets. However, some research has found that a mother's fish consumption during pregnancy, or the baby's consumption of it early on, may lower the risk of asthma.
Using health and diet information from a group of 7,210 children born between 2002 and 2006 in Rotterdam, the researchers found that 1,281 children ate fish in their first six months of life, 5,498 first ate fish in the next six months, and 431 did not eat fish until after age one.
The researchers then looked at health records for when the children were about four years old, and how many parents reported that their children were wheezing or short of breath.
Between 40 percent and 45 percent of parents of children who did not eat fish until after their first birthdays said their children wheezed, compared to 30 percent of children who first ate fish when they were between six and 12 months old.
That, the researchers said, works out to about a 36 percent decreased risk of wheezing for the children who first had fish between the ages of six months and one year.
Children who first had fish before six months of age were at similar risk to those who were introduced to it after their first birthdays.
"They found it was only protective between six and 12 months," said T. Bernard Kinane, chief of the pediatric pulmonary unit for MassGeneral Hospital for Children in Boston, who was not involved in the study.
"That would make reasonable sense because that's when the immune system is getting educated."
He added that he was relieved the researchers also found no association between the amount of fish children ate and their risk for asthma, which means that even a small amount of fish seems to be helpful.
But he noted that there is mixed evidence about how helpful introducing a seafood diet actually was, and that while it may be helpful to introduce children to fish between six and 12 months of age, there could be other factors at work.
For instance, families who feed their children fish earlier and more often may be different in a variety of ways from those who do not.
"I think (the study) needs to be validated again," he said.
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