Nursing mothers, especially those who go back to work, often pump their breast milk so that their babies can drink it from a bottle. A new study suggests, however, that if the milk is chilled for too long, it may lose some of its health benefits.
Writing in The Archives of Childhood Disease, researchers said the antioxidants in breast milk that had been refrigerated were less active than those in fresh breast milk. Milk that had been frozen showed even less activity, the study said. The researchers stressed, however, that the implications of the findings were not clear.
"The important thing is, 'So what?' " said the lead author, Dr. Thomas Hegyi of the Robert Wood Johnson Medical School in New Brunswick, N.J. Hegyi said that mothers should continue to breast-feed if they could, and that they should go ahead and refrigerate or freeze the milk.
Still, the study's findings suggested that storing breast milk at low temperatures for more than a couple of days can reduce the strength of its antioxidants, which help the body fight disease. When the researchers looked at refrigeration's effect on infant formula — which has less antioxidant activity than breast milk does — they didn't see the same effect.
The findings were based on an examination of 16 samples of milk collected from mothers who had delivered within the previous 24 hours. After the milk was checked for antioxidant activity, the researchers refrigerated some and froze the rest. Then they rechecked the antioxidant activity after two days and after seven days. The antioxidant activity was reduced at four days and even more at seven.