Why do some women breastfeed and others don't? Family culture can play a role in that decision, researchers say - as can hospitals that introduce formula to newborns.

Breastfeeding rates are known to differ among racial and ethnic groups in the U.S. Now, the researchers report, their new study suggests that Hispanic women are encouraged to breastfeed by relatives, while black mothers are discouraged from breastfeeding by hospitals that introduce formula to their babies.

Breastfeeding offers the best nutrition for infants. That's why the American Academy of Pediatrics recommends nothing but breastfeeding for the first 6 months of life, with continued breastfeeding, along with the gradual introduction of food, at least until the child's first birthday.

But even with these recommendations, about half of U.S. infants are no longer breastfed by 6 months, and only a few receive the recommended 12 months.

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A 2012 study found that more than 80 percent of white and Hispanic mothers start breastfeeding, and more than 50 percent are still breastfeeding at 6 months. But only about two thirds of black mothers start breastfeeding, and just over a third are still breastfeeding at 6 months.

To learn more about those differences, Dr. Chelsea O. McKinney from NorthShore University HealthSystem in Evanston, Illinois and her team used information collected from 1,636 mothers in Maryland, Illinois and the District of Columbia.

Compared with non-Hispanic white mothers, black mothers had higher rates of poverty and were less likely to have a college degree or to be married, and these three differences fully explained the lower rates of intending or starting to breastfeed among black mothers.

Even when they started breastfeeding, black mothers weaned their infants about 10 weeks earlier than white mothers, and the biggest reason was that black mothers were more likely to start using infant formula while in the hospital.

"I think eliminating infant formula use in hospitals, unless there is a medical need, would make the most impact on breastfeeding disparities that have plagued the U.S. for decades," McKinney said in an email. "Limited formula feeding in the hospital would likely improve breastfeeding outcomes for African Americans, as we found in our study, but also for mothers of any race/ethnicity, as we've seen from the success of many baby-friendly hospitals."

Hispanic mothers, whether they spoke Spanish or English, were more likely than white mothers to start breastfeeding. The fact that Hispanic mothers more often had female relatives who breastfed fully explained this difference.

Hispanic mothers were also more likely than black mothers to start breastfeeding and to breastfeed longer. Again, the higher rates of breastfeeding among relatives of Hispanic mothers explained most of these differences, the authors reported in Pediatrics.

"It was interesting to see family history of breastfeeding play such a strong role for Hispanic mothers," McKinney said. "These findings really illustrate how culture influences health and the intergenerational transmission of health behaviors."

She concluded that eliminating infant formula and asking about the mother's family history of breastfeeding would help health care providers to better support women who lack breastfeeding experience and would go a long way toward eliminating these racial differences and improving breastfeeding outcomes overall.