22 March 2013. A mother should breastfeed her child for at least 6 months, says the World Health Organization, and this advice is repeated by health experts around the world. Indeed, many studies show that infants nursed for longer periods are in several respects healthier than those not or only briefly breastfed. A new study from Quebec, Canada shows that breastfeeding is associated with increased thickness of the gray matter of the brain in adolescents. Especially the parietal lobes benefited from mother’s milk. Breastfeeding also seems to increase the child’s IQ, the researchers found, as had been seen in several previous studies.
Although plausible, these findings need to be cautiously interpreted, one problem being that infants not breastfed may have been less healthy to begin with. Also, the closer contact between mother and breastfed child may by itself confer developmental advantages. Still, we do know that human milk in many ways is superior to formula milk due to the content of essential nutrients crucial for the child’s development. But that is not the whole story.
Human milk also contains contaminants, especially lipid-soluble pesticides and industrial chemicals. In some cases, the concentrations in human milk exceed legal limits so that it would be illegal to market the milk as food. As the mother transfers part of her body burden of these substances to her child, there is a shift in serum concentrations: The child may end up with higher pollutant concentrations in the blood than the mother has – and the child’s brain is highly vulnerable to many of these chemicals.
This is not to say that breastfeeding is a bad idea – on the contrary. But lengthy breastfeeding is not as advantageous as it could have been. And changing to formula is not necessarily an improvement, especially when the formula is made with drinking water that has its own content of contaminants. This situation has been referred to as the weanling’s dilemma. Most of the time, breast is probably best, at least for some months. But the data are somewhat uncertain: Studies that focus on breastfeeding advantages almost never consider the possible impact of chemical contaminants. However, environmental epidemiology data show that brain development may be negatively affected by postnatal exposures to substances such as PCB that are transferred from the mother via her milk.
Even when the World Health Organization collated the documentation for recommending exclusive breastfeeding for 6 months, not a single mention of pollutants was made. The advantage associated with breast milk varied considerably between studies – could it be that some populations are more exposed to toxic chemicals and that the average benefits are therefore less? Unfortunately, the new study is no better in this regard. The only ‘exposure’ that was considered was maternal smoking during pregnancy (yes, it seems to have a negative influence on brain development).
We are therefore back at the weanling’s dilemma: Is it better to rely on the mother’s nutritious milk that comes along with accumulated concentrations of persistent pollutants, or is it preferable to rely on external sources that may differ both in respect to nutrients and to brain-draining chemicals? In most circumstances, there can be little doubt that breast-feeding for some months is beneficial to the infant and, in particular, the developing brain. So breastfeeding is likely to be the best for the child, especially during the first few months. But if human milk was free of chemical contaminants, human milk would no doubt be the ideal brain food at the beginning of postnatal life.