Breast feeding in infancy and social mobility: 60-year follow-up of the Boyd Orr cohort.

OBJECTIVE: To assess the association of having been breast fed with social class mobility between childhood and adulthood.
DESIGN: Historical cohort study with a 60-year follow-up from childhood into adulthood.
SETTING: 16 urban and rural centres in England and Scotland. PARTICIPANTS: 3182 original participants in the Boyd Orr Survey of Diet and Health in Pre-War Britain (1937-39) were sent follow-up questionnaires between 1997 and 1998. Analyses are based on 1414 (44%) responders with data on breast feeding measured in childhood and occupational social class in both childhood and adulthood. MAIN OUTCOME: 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.
RESULTS: The prevalence of breast feeding varied by survey district (range 45-86%) but not with 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. Participants who had been breast fed were 41% (95% CI 10% to 82%) more likely to move up a social class in adulthood (p = 0.007) than bottle-fed infants. Longer breastfeeding duration was associated with greater odds of upward social mobility in fully adjusted models (p for trend = 0.003). Additionally controlling for survey district, household income and food expenditure in childhood, childhood height, birth order or number of siblings did not attenuate these associations. In an analysis comparing social mobility among children within families with discordant breastfeeding histories, the association was somewhat attenuated (OR 1.16; 95% CI 0.74 to 1.8).
CONCLUSIONS: Breast feeding was associated with upward social mobility. Confounding by other measured childhood predictors of social class in adulthood did not explain this effect, but we cannot exclude the possibility of residual or unmeasured confounding.