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More than 80 percent of U.S. mothers breastfeed their newborns, a new survey finds, but fewer than a third keep doing so for the recommended minimum of one year, a new survey finds.

Many studies support breastfeeding for as long as possible, and the American Academy of Pediatrics recommends that babies get nothing but human breast milk until the age of six months — and that they continue to breastfeed for at least a year.

Mother breast-feeding her baby 1 month old. Lita Bosch / Getty Images

“Breastfeeding decreases the possibility that your baby will get a variety of infectious diseases, ear infections, diarrhea, etc.,” the Academy says in its guidance.

“Breastfeeding mothers return to their pre-pregnancy weight faster and have a reduced risk of breast and ovarian cancer.”

But American women struggle to breastfeed for that long.

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Related: Survey Shows Big Drop in Baby Formula Giveaways

The survey from the Centers for Disease Control and Prevention found that 81 percent of U.S. babies born in 2013 were breastfed from birth. “This high percentage of babies who start out breastfeeding shows that most mothers want to breastfeed and are trying to do so,” the CDC said in a statement.

“More than half (51.8 percent) of infants were breastfeeding at six months,” it added. That's up significantly from just 35 percent of women in 2000.

But then it drops off. “Less than a third (30.7 percent) of infants were breastfeeding at 12 months,” the CDC said.

Related: Kids Breastfed Longer Have Higher IQs

While there are many reasons, a big one is that so many working women find it hard to continue breastfeeding.

About two-thirds of U.S. women are employed while pregnant and only about 70 percent of them report taking some time off, according to the National Center for Health Statistics. The average maternity leave in the U.S. is about 10 weeks.

“We are pleased by the large number of mothers who start out breastfeeding their infants,” said Dr. Ruth Petersen, director of CDC’s Division of Nutrition, Physical Activity, and Obesity. “Mothers can better achieve their breastfeeding goals with active support from their families, friends, communities, clinicians, health care leaders, employers, and policymakers.”

Related: Half of New Moms Now Breastfeed

Studies show that babies given nothing but breastmilk for the first four months of life have a 72 percent lower risk of severe pneumonia for their first year. If moms stop breastfeeding between four and six months, their babies have four times the risk of pneumonia compared to moms who breastfeed for a year or longer.

Not only does breastmilk contain the nutrients that a newborn baby needs, it also transfers disease-fighting antibodies from mother to baby — something that’s very important for the first few months before an infant can be vaccinated.