We read with great interest the recent study by Mayer-Davis et al. (1) on the impact of breast-feeding on childhood obesity risk in the presence of maternal diabetes or obesity. The authors drew conclusions that seem to directly oppose previous observations from our group (2,3). However, we would like to deliver three arguments suggesting that the presented data can also be interpreted in a completely different manner and in no way exclude, but rather support, a potentially negative dose-depending effect of early neonatal breast-feeding on overweight risk in offspring of diabetic/overweight mothers, as observed by us.
First, the majority of fully adjusted estimates for the effect of maternal diabetes have 95% CIs that include decreased as well as increased odds ratios over a wide range (e.g., odds ratio 0.79 [0.29–2.16] for breast milk only vs. formula only). By statistical definition, one therefore cannot exclude the possibility that the true effect of breast-feeding on overweight risk in the presence of maternal diabetes/obesity is not beneficial but deleterious, at least in a considerable number of cases.
Second, breast-feeding during the 1st month by diabetic mothers increased overweight risk compared with formula feeding. This, in fact, confirms rather than rejects our observations. Moreover, this is unlikely to be accounted for by reverse causation, since no dose response–like relation between duration of breast-feeding and risk of overweight was observed in offspring of diabetic mothers. These data may even support our hypothesis of a crucial and probably even deleterious impact of breast-feeding by diabetic mothers during the early neonatal period.
Finally, the authors stated that our observations might reflect “appropriate” growth rather than untoward effects. This, however, does not correspond with increased prevalence of overweight in the highest tertile of early neonatal intake of diabetic breast milk, using the symmetry index (2) additionally validated against BMI (4). Most importantly, this interpretation completely ignores deleterious effects on glucose tolerance resulting from increased relative weight, as also observed in our study (2).
We strictly support the statement of Mayer-Davis et al. (1) that breast-feeding should be recommended for all women. However, against the background of the rather exemplary arguments provided here, this story is far from being finished. Much more research is urgently needed, especially to ensure safety of our general recommendation also in the case of early neonatal breast-feeding by diabetic/overweight mothers.
