THURSDAY, Oct. 20, 2004 (HealthDayNews) -- Breast milk is better than formula, but a new study says it loses some of its best properties once it's refrigerated.
While breast milk has more antioxidants than formula, fresh breast milk boasts a higher level of antioxidants than refrigerated or frozen breast milk does, according to the study appearing in the Fetal and Neonatal edition of the Archives of Disease in Childhood.
"We found that breast milk has more antioxidant capacity than formula milk, but if you store it and freeze it, it will lose some of those properties," said study author Dr. Thomas Hegyi, program director of Neonatology at the University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School.
But Hegyi quickly added that he's not trying to make mothers feel guilty about having to store milk, or for using formula. "Breast milk is good. Fresh breast milk is optimal, but if you can't, that's OK," he said, adding that many babies have grown up fine on formula.
However, in the study, Hegyi and his colleagues did note that getting extra antioxidants may be more important for premature infants. Babies born prematurely don't have as great an antioxidant capacity as full-term infants do. They also have more oxidative stress and, thus, a greater need for antioxidants than full-term babies, according to the study.
To test the antioxidant capacity of breast milk, samples were gathered from 16 mothers within 24 hours of delivery. Half of the mothers delivered their babies at term, and the other half delivered prematurely. These samples were tested for their antioxidant capacity when they were fresh, then after refrigeration for 48 hours and for seven days, and finally after being frozen for 48 hours and for seven days.
Additionally, the researchers tested five different formula samples and found the antioxidant capacity between the different formulas was nearly the same. Also, the researchers found that the antioxidant capacity was similar in the milk from mothers who gave birth prematurely and in mothers whose babies were born at term.
Fresh human milk, whether it had been refrigerated or frozen, had a significantly higher antioxidant capacity than formula.
Antioxidant levels fell in breast milk the longer it was stored. And the colder the sample was, the lower the antioxidant level was. Antioxidant levels in formula remained constant whether fresh, refrigerated or frozen.
"This study doesn't surprise me," said Angela Kurtz, a pediatric nutritionist at New York University Medical Center. "When we look at fresh food, water-soluble vitamins are often lost with cooking, storage, etc. Water soluble vitamins are so sensitive to their temperature and environment."
Kurtz also pointed out that the mother's diet can change her antioxidant levels, and that heating breast milk can also reduce the amount of antioxidants present. She recommended running bottles under warm water, and said parents should never place a bottle in boiling water or in the microwave.
Katy Lebbing, manager of the Center for Breast-feeding Information for La Leche League International in Schaumburg, Ill., agreed the study results weren't surprising.
"We've known that with storage, either in the refrigerator or freezer, we do lose some nutrients," said Lebbing. But, she added, there may not be much a mother can do to alter her storage habits if she works. Lebbing also pointed out that the study reinforces the value of breast milk, and said "breast milk is the gold standard."
Hegyi and his colleagues recommended that if possible, breast milk shouldn't be frozen, and if stored in the refrigerator, they suggest using it within 48 hours for the highest antioxidant levels.
More information
For more information on storing breast milk, visit the National Women's Health Information Network.
