Breast-fed children in the United States are 20 percent less likely to die during the first year of life than those who are not nursed, according to a study released on Sunday.

Researchers at the National Institute of Environmental Health Sciences said they based their finding on a survey that included nearly 9,000 infant deaths in 48 states.

It found breast-fed babies were 20 percent less likely to die between 1 and 12 months of life than those who were not, and that the longer babies were breast-fed, the lower the risk of early death.

Aimin Chen, a physician who was one of the authors of the study, said in an interview that the protective effect appears to come from the “package of child care skills” that goes along with nursing as well as the benefits of the milk.

He said data from 2000 show that 70 percent of U.S. newborns are breast-fed when they leave the hospital and at 6 months almost one third are. But there are still racial and economic disparities in how widely the practice has been adopted.

Other studies have shown breast-fed babies are less likely to be overweight, have fewer behavioral problems and may show differences in intelligence. They also may grow up to have lower blood pressure.

Groups such as the American Academy of Pediatrics recommend that all mothers breast-feed their babies for the first year, and two years if possible.

The study was published in the May edition of Pediatrics, the journal of the American Academy of Pediatrics.