Maternal diet and breastfeeding: A case for rethinking physiological explanations for breastfeeding determinants

Background: Although some authors explain determinants of breastfeeding that occur in a dose-response manner as evidence of causality, we argue that dose-response relationships are not proof of a biological relationship between the variables. The relationship between maternal smoking and breastfeeding and maternal obesity and breastfeeding are similar: increasing levels of smoking or obesity are associated with shorter duration of breastfeeding. However, maternal infant feeding intention is a strong predictor of breastfeeding duration. Aims: In this paper we present data on another variable with a clear dose-response relationship with breastfeeding duration - maternal diet - as a case study to argue that a dose-response relationship does not imply causality. Study design: Secondary analysis of cross-sectional survey. Subjects: Nationally representative sample of 3544 singleton infants in Longitudinal Study of Australian Children, 2004. Outcome measures: Maternal intake of fruit and vegetables; breastfeeding duration. Results: Adjusted Odds Ratios (AOR) for breastfeeding at 6 months for daily maternal fruit and vegetable intake (reference group = no fruit/vegetables): 1 serve AOR 1.6 (95%CI 1.0, 2.6); 2 serves AOR 23 (1.5, 3.5); and 6 or more serves AOR 4.4 (2.8, 6.8). Conclusions: Although higher maternal intake of fruit/vegetables is associated with longer breastfeeding duration, this is not a biological causal relationship. There are possible biological explanations for altered milk supply in women who smoke or are obese, but not for fruit/vegetable intake. We call for a broader understanding of the social determinants of infant feeding and suggest that all breastfeeding studies measure maternal infant feeding intention as an important determinant. (C) 2011 Elsevier Ireland Ltd. All rights reserved.