Breastfeeding is known to help ward off infections among infants, but a new U.S. study suggests that protection may be much longer lasting.

Among thousands of 6-year-olds followed from birth, those who were breastfed as babies were far less likely to have ear, sinus or throat infections later in childhood. And the longer the children were breastfed during their first year, the lower their odds of those infections at age 6.

“This study provides hard evidence that health benefits of breastfeeding go beyond infancy and breastfeeding seems to be the best prescription for preventing these infections,” said Dr. Ruowei Li, an epidemiologist at the Centers for Disease Control and Prevention (CDC) in Atlanta, who led the study.

Ear infections account for at least 24 million clinic visits a year in the U.S., Li told Reuters Health in an email, and there are up to 1 billion cases of acute sinus infection each year.

Following-up on babies who were part of a breastfeeding study in the past provided a unique opportunity to see if there were long-term benefits from having been breastfed, she said.

Li and colleagues used data from women who were originally enrolled in the large Infant Feeding Practices Study II, which was conducted by the U.S. Food and Drug Administration and CDC in 2005 - 2007.

The researchers contacted 1,281 of the mothers in 2012, when their children were about 6 years old, and asked about the number and types of common infections the children had in the previous 12 months. They also asked how many times the child had been to the doctor’s office.

The study team found that 66 percent of the children had colds or upper respiratory tract infections in the past year, 25 percent had ear infections, 24 percent had throat infections and 16 percent had sinus infections. Lung and urinary tract infections were not as common.

When Li’s team compared kids based on whether and how long they were breastfed, they found that about 15 percent of children who were breastfed had sinus infections compared to 22 percent of non-breastfed kids.

About 24 percent of kids who were breastfed had throat infections, versus 30 percent of those who were never breastfed. And 25 percent of kids who were breastfed had ear infections, compared to 28 percent of kids who were not breastfed, according to the results in the journal Pediatrics.

There were no differences in the number of cases of colds, upper respiratory tract infections, pneumonia or other lung infections.

But for ear, throat and sinus infections, the researchers found that the longer children were breastfed, the lower their odds of those infections. Kids breastfed for at least 9 months as infants had one-third to one-half as many cases as kids breastfed for 0 to 3 months.

“This study suggests that the longer a mother breastfeeds and waits to introduce foods and drinks other than breast milk, the lower the odds her child will have ear, throat and sinus infection,” Li said.

She and her coauthors speculate in their report that some factors in breast milk might stimulate an infant’s developing immune system in ways that have enduring effects.

They also acknowledge that some other reason might explain the lower number of infections among children who were breastfed.

Li said the American Academy of Pediatrics (AAP) recommends exclusive breastfeeding for an infant’s first 6 months, followed by continued breastfeeding until at least 12 months old with nutrient-rich foods introduced in addition to breastfeeding starting at 6 months.

“Mothers need to be supported by health care professionals, their workplaces and communities to follow AAP recommendations on breastfeeding,” Li said.