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Dr. Richard M. Martin and colleagues from the University of Bristol found that individuals who had been breastfed were 41 percent more likely to move up at least one social class during their lives.

Breastfeeding has a number of health benefits, and may also boost intelligence while reducing the risk of psychiatric problems, Martin and his team note in the Archives of Disease in Childhood. They tested their hypothesis that being breastfed might affect upward social mobility by looking at 1,414 men and women who had participated in a pre-World War II study of diet and health and were followed up 60 years later.

Social class in childhood was based on the occupation of the male head of the household, while participants' social class as adults was based on their own occupation. Martin and his colleagues used three social class categories: I/II, professional and managerial; III, skilled; and IV/V, partly skilled, unskilled, other and unemployed.

The researchers found no association between breastfeeding and household income, social class or the amount of money a household spent on food. Seventy percent of all study participants had been breastfed.

Fifty-eight percent of the individuals who had been breastfed had moved up a social class level by the study follow-up, compared to 50 percent of those who had been bottle-fed, the researchers found.

In addition, 61 percent of those who moved down a social class had been breastfed, while 68 percent of those who remained at the same class level had been breast-fed and 74 percent of those who moved up had been breastfed.

Individuals who had been breastfed were more likely to have competed secondary school, which accounted for some but not all of the effect of breastfeeding on social mobility.

When the researchers compared breastfed and bottle-fed infants within the same family, the effect on social mobility was weakened but still significant.

While breastfeeding in the 1920s and 1930s wasn't as strongly tied to a mother's social class and education as it is now, the researchers note, "it remains possible that mothers from that era who chose to breastfeed their children differed from those who did not with respect to factors associated with improved occupational prospects." They also note that the current study did not include information on mothers' educational level.

"The relevance for 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 related to social mobility, such as growth, health or IQ," they add. However, given that other, unknown factors may account for the results, they conclude, more study is needed.