Breast Milk Boosts the Upwardly Mobile Set

BRISTOL, England, Feb. 14 -- Breast milk may fuel high-octane social ambition, or so it seems.

That's the conclusion of researchers here, who reviewed the lives of those in their 60s and 70s, and found that breastfed infants had been significantly more likely to climb above their social station as adults than those who had been bottle-fed.

"We found that ever having been breast fed was positively associated with increased odds of upward social mobility in this cohort born in the 1920s and 1930s when there was little social patterning in infancy of breast feeding," wrote Richard Martin, Ph.D., and colleagues of the University of Bristol.

The salutary effects of breast milk on cognitive development could help those who were breast fed attain higher levels of education and better jobs, leading to upward social mobility, the authors suggested online in the Archives of Disease in Childhood.

The authors found men and women who had been part of the Boyd Orr Survey of Diet and Health in Pre-War Britain, which ran from 1937 to 1939. The survey looked at the nutrition and health of 4,999 children from birth to age 19 from 1,343 families in 16 urban and rural centers in England and Scotland.

About sixty years later, Dr. Martin and colleagues mailed questionnaires to 3,182 members of the original cohort, and received 1,414 responses (44%) from people for whom data on breast feeding measured in childhood, and information about occupational social class in both childhood and adulthood were available.

The study's primary outcome measure was the "odds of moving from a lower to a higher social class between childhood and adulthood in those who were ever breast fed versus those who were bottle fed."

The authors defined social class in adulthood based on the participants' main employment for men and for unmarried women. Job status was classified according to the 1996 International Standard Classification of Occupations.

The authors found that that from 1937 to 1939, breast-feeding prevalence varied by district, ranging from 45% to 86%, but there were no significant differences in prevalence according to household income (P=0.7), expenditure on food (P= 0.3), number of siblings (P=0.7), birth order (P=0.5) or social class (P= 0.4) in childhood.

They also found that "participants who had been breast fed were 41% (95% confidence interval 10% to 82%) more likely to move up a social class in adulthood (P=0.007) than bottle-fed infants."

In multivariate logistic regression models the authors found that longer breast feeding duration was associated with greater odds of upward social mobility (P for trend = 0.003).

When they controlled for age, sex, survey district, per capita weekly food expenditure, household income, number of siblings, birth order, and childhood height, they that found that the association between breast-feeding duration and upward mobility was unchanged.

When they restricted analysis to those families in which only some of the children were breastfed, there was still a positive association between upward social mobility and breast feeding, although the association was weaker, and non-significant with wide confidence intervals, the authors noted (odds ratio in fully adjusted models, 1.16, 95% CI., 0.74 to 1.8).

"Our original hypothesis was that if breast feeding really does improve health, and increase stature and IQ (as reported in many epidemiological studies), then breastfed infants might be more likely to show upward social mobility than those who were bottle fed," the authors wrote.

"The relevance of this finding for contemporary children, therefore, is that it provides indirect support for the suggestion that having been breast fed may have long-term effects via associations with intermediate factors related to social mobility, such as growth, health or IQ."

They acknowledged, however, that the within family analysis where the OR was attenuated suggests that their results may be limited by residual or unmeasured confounding and breast feeding may therefore be a marker for other factors that explain upward social mobility. Further investigations are therefore necessary before they can conclusively link breast milk to social status.