Breastfeeding Improves Stress Response Later in Childhood

STOCKHOLM, Aug. 3 -- Breastfeeding in infancy, even briefly, may help children later bounce back from stressful events like parental divorce.

Breastfed babies were 7% less likely to be anxious at age 10 following divorce, or separation of their parents, than those who were bottle fed, researchers reported online Aug. 3 in the Archives of Disease in Childhood.

"Our results indicate that some exposures associated with breastfeeding may also be associated with development of the stress response in human infants," wrote clinical epidemiologist Scott M. Montgomery, Ph.D., of the Karolinska Institute in Stockholm.

The observational study analyzed data from the 1970 British Cohort Study that is following everyone born in Great Britain during a one-week period in 1970. The analysis included 5,671 children who were fed formula as infants and 3,287 who were fed breast milk.

Mothers were interviewed around the time of the child's birth, both parents were interviewed five years later, and at age 10 medical exams and chart reviews were done for the children along with interviews of the mothers. At the 10-year mark, teachers ranked each child's anxiety on a scale of one to 50, with 50 extremely anxious. This ranking formed the basis for the current analysis.

The researchers found that breastfeeding was associated with a modest but non-statistically significant decrease in the risk of anxiety.

However, there was a significant and marked difference in anxiety between the 10.7% of breastfed and 12.9% of bottle fed children whose parents had separated or divorced when they were between five and 10 years old. Divorce prior to the child's fifth year was excluded to minimize confounding factors in the mother's decision to breastfeed her child.

An a comment on the study, Joan Y. Meek, M.D., of the Arnold Palmer Hospital for Children and Women in Orlando said that even a small reduction in childhood anxiety levels may be important.

"In our increasingly complex world with stressors occurring at early ages, a small, but significant reduction in anxiety may be more cost effective than pharmacotherapy or mental health counseling," she said.

The coefficient of association between parental divorce and anxiety at age 10 was significantly higher for children who had been bottle- versus breastfed (9.4 versus 2.2, P?0.0001).

"The substantial difference in the coefficients of association indicates effect modification," wrote Dr. Montgomery, which he said shows that breastfeeding is a factor that increases resilience and reduces the effect of the stressful event.

This relationship remained significant despite controlling for potentially confounding factors such as social class, mother's age at leaving full-time education, maternal depression, number of older siblings, premature birth and smoking during pregnancy.

Dr. Montgomery cautioned that breastfeeding or breast milk itself may not necessarily be what confers this resilience to stress. Rather, he said, it may be just a "useful indicator" of exposure to factors like maternal contact or family characteristics that confer lower levels of anxiety.

However, a direct relationship between breastfeeding and stress levels appears plausible. Animal studies have suggested that breast feeding promotes the development of neuroendocrine systems involved in the stress response and other studies have found that the hormone leptin in breast milk may reduce stress in infants.

Interestingly, there did not appear to be a dose-response effect for breast feeding and stress levels. The likelihood of an interaction between divorce and duration of breast feeding was not significant (-1.5 for a duration of more than a month versus -1.3 for a duration of less than a month).

These findings enhance the already extensive literature showing health, nutritional, immunologic, developmental, and psychological benefits of breastfeeding for babies and mothers. The American Pediatrics Association advocates breastfeeding as do other governmental and professional associations.

Even so, some individuals decide not to breastfeed for a variety of reasons, Dr. Meek said.

"There are still many parents, as well as health care professionals, who view breastfeeding and formula feeding as equivalent options and who fail to acknowledge that the choice of infant feeding is not just a lifestyle choice, but an important health care initiative, with both short term and long term consequences," she said.