Breast-feeding is considered a great way for a mother to form a close bond with her infant. And now there's evidence to suggest it may also help kids be more resilient to stress.

Researchers in Sweden and the United Kingdom examined data on almost 9,000 children born in Britain in 1970. Relevant information was collected at birth and again at ages 5 and 10 from parents, teachers, health care workers and midwives.

Teachers were asked to rate the kids' anxiety levels on a zero-to-50 scale at age 10. And parents were asked about major life events — including divorce or separation — that occurred when their children were between 5 and 10 years old.

Not surprisingly, children whose parents had divorced or separated were more likely to have high anxiety. But what the researchers found striking was the difference in stress levels between breast-fed and bottle-fed kids. Breast-fed children were significantly less anxious than kids who hadn't nursed at their mother's breast.

Lead author Scott Montgomery, an associate professor at the Karolinska Institutet in Stockholm, said the research team was interested in examining whether there are any specific early-life exposures that make children better able to cope with stress later in life. The study attempted to replicate animal studies that showed close physical contact between a mother and her offspring may have a positive impact on the development of the offspring's stress response, he said.

"The best marker of maternal physical contact in the first month of life that we could find among the research information at our disposal was breast-feeding," Montgomery said.

Breast-feeding offers many health and development benefits for babies, says the National Institute of Child Health and Human Development. Kids get the right balance of nutrients to support optimal growth, fatty acids to promote brain development and protection against many childhood illnesses. And there are important emotional and physical benefits for moms as well.

"There is no question that breast-feeding is better for the health of mothers and children," said Nicole Else-Quest, an assistant professor of psychology at Villanova University in Pennsylvania, "but it is less clear how breast-feeding affects the mother-child relationship." Breast-feeding may help to establish an early bond, she added, but "it is only one of many ways to do so."

The research team considered factors that might affect a child's reaction to stress and ability to cope, such as maternal depression, parental education levels, social class and smoking habits. Even after accounting for those factors, breast-fed children were less anxious than their peers. In addition, bottle-fed children whose parents divorced were more anxious than breast-fed kids.

Yet the study findings don't prove that breast-feeding itself reduces anxiety. It may be a mark of close, early physical contact, the researchers noted.

"A child without such regular contact may perceive greater danger reacting to stress — indicating a potentially dangerous situation — with a more reactive and less well-controlled stress response," Montgomery said.

It's also possible, he added, that mothers who breast-fed simply have a better relationship with their child.

"The parent-child relationship influences the child's health and development in many ways," Montgomery said. "A good relationship with parents is important, and this relationship begins in infancy, so good early contact with the child is important."

The study findings were published in the journal Archives of Disease in Childhood.