Over 3000 children from 16 rural and urban areas across England and Scotland were monitored from birth, as part of the Boyd Orr Study of Diet and Health in Pre-War Britain (1937-1939).
The study results are based on 1414 people in their 60s and 70s, for whom information on breastfeeding in infancy and changes in social class was available.
The prevalence of breastfeeding varied from 45 per cent to 85 per cent, but was not dependent on household income, expenditure on food, number of siblings, birth order, or social class in childhood.
But those who had been breastfed as babies were 41 per cent more likely to move up the social ladder as adults than those who had been bottle fed.
The longer a child was breastfed, the greater were their chances of upward mobility, the results showed.
The findings held true even after taking account of other factors likely to influence the results.
Potential benefits of breastfeeding
The authors suggest that the findings might be explained by the potential benefits of breastfeeding confers on brain development, which might then lead to better exam and job prospects, and greater earning potential.
But other as yet unknown social and economic factors associated with breastfeeding may explain the findings, they say.
Breastfeeding may also improve long term health, which is associated socioeconomic factors.