Bonding benefits of breastfeeding extend years beyond infancy

The results held even after accounting for maternal neuroticism, parenting attitudes, ethnicity, mother's education and presence of a romantic partner. The findings are published in the journal Developmental Psychology.

"It was surprising to us that breastfeeding duration predicted change over time in maternal sensitivity," said the study's lead author, Jennifer Weaver, PhD, of Boise State University. "We had prior research suggesting a link between breastfeeding and early maternal sensitivity, but nothing to indicate that we would continue to see effects of breastfeeding significantly beyond the period when breastfeeding had ended."

Maternal sensitivity was defined as the synchronous timing of a mother's responsiveness to her child, her emotional tone, her flexibility in her behavior and her ability to read her child's cues.

Even though increased breastfeeding duration led to greater maternal sensitivity over time, the effect sizes were small, according to the article. That means the close interaction experienced during breastfeeding may be only one of many ways the bond is strengthened between mother and child, according to Weaver.

The researchers analyzed data from interviews with 1,272 families who participated in the National Institute of Child Health and Human Development's Study of Early Child Care. Recruited from 10 sites around the U.S. in 1991 when their infants were a month old, mothers completed a home interview and became part of the initial study sample. The sample included a substantial proportion of less-educated parents (30 percent had no college education), and ethnic minority families (13 percent were African-American).

Women in the study breastfed for an average of 17 weeks. Fewer than 1 percent breastfed for 24 months and 29 percent didn't breastfeed at all. Researchers interviewed and videotaped families in their homes periodically until their child turned 11.

As part of the study, parents interacted with their children during free play scenarios and age-appropriate problem-solving tasks. For example, at the six-month visit, parents and babies played with a set of toys and, when the children were 4, they would complete a maze together. When the children were in fifth grade, mothers talked to their child about an area of possible disagreement, and also worked with their child to build a tower out of toothpicks. Researchers rated the quality of the collaborative interaction, such as the mother's level of support, respect for her child's autonomy and levels of hostility.

While fathers participated in the home interviews, there was no correlation between the mother's breastfeeding length and men's sensitivity toward their children.

The study is not intended to diminish the bonding experiences of women who are not able to breastfeed, said Weaver. "Ultimately, I do hope that we will see breastfeeding examined more closely as a parenting factor, not just as a health consideration, to allow us to more fully understand the role that breastfeeding plays in family life."