NEW YORK - Breast milk can be refrigerated for up to four days without losing its nutritional value or allowing bacteria to build up, a small study suggests.

Guidelines on safe storage of breast milk vary somewhat. But in general, it's thought that breast milk can be refrigerated at 39 degrees Fahrenheit for as long as five to eight days, though it should ideally be used within two or three days.

However, much of the research on breast-milk storage has focused on the risk of bacterial buildup -- and not the overall integrity of the milk, according to the researchers on the new study, led by Dr. Richard J. Schanler of North Shore University Hospital in Manhasset, New York.

To study the question, the researchers stored breast-milk samples from 36 mothers in the refrigerators of one neonatal intensive care unit (NICU). The milk, which mothers collected with a breast pump about one month after giving birth, was stored at 39 degrees F and tested after 24, 48, 72 and 96 hours.

Over that time, the researchers found either no or minimal changes to the breast milk's composition -- including bacterial levels, acidity, immune-system proteins from the mother, beneficial fatty acids and protein.

The findings suggest that fresh breast milk can be refrigerated for up to 96 hours without compromising its integrity, Schanler and his colleagues report in the Journal of Pediatrics.

While the study was conducted in a NICU, the results fit in with the typical recommendations for home refrigeration of breast milk -- that it's best to use the milk within a few days, though a somewhat longer period may be safe.

When it comes to home storage, experts generally advise using clean, dry glass containers or plastic ones free of the chemical bisphenol A.

Each container should be labeled with the date and placed at the back of a refrigerator set at 39 degrees or cooler.

SOURCE: Journal of Pediatrics, January 2010.