Pollutants in breast milk may fluctuate during nursing.

Aug 11, 2009

LaKind JS, CM Berlin Jr., A Sjodin, W Turner, RY Wang, LL Needham, IM Paul, JL Stokes, DQ Naiman, and DG Patterson Jr. 2009. Do human milk concentrations of persistent organic chemicals really decline during lactation? Chemical concentrations during lactation and milk/serum partitioning. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.0900876

Synopsis by Michele A. La Merrill, Ph.D.

Levels of contaminants in breast milk are more complicated than once thought; instead of a constant decline during nursing, levels may fluctuate from beginning to end, finds a new study that contradicts the long-held belief that the pollutants steadily wane.

Breast milk continues to be contaminanted with chemical pollutants that collect in fat. These pollutants include flame retardants, dioxins and pesticides. The concentration of these fat-loving chemicals in a woman’s milk may not simply decrease over the course of her breast feeding. At least, not consistently, according to a study that counters long-held beliefs and most prior research results.

This is the first of many published studies about chemical pollutants in breast milk that finds the chemical levels do not relate to the length of time a woman has breast fed. More, larger studies are necessary to confirm if other factors – such as diet, weight loss, fat levels and chemical breakdown – play a role in how the pollutants transfer from a mother, to her breast milk, and ulitmately, to her baby, over time.

Breast milk is perfectly formulated for an infant’s needs, supplying all the necessary components for the healthy growth of infants. Mothers milk contains her antibodies, which help infants fight infection, and is rich in sodium, iron, protein and fat.

The milk fat helps the infant grow fast. Unfortunately, the milk fat is also contaminated with pollutants that had accumulated in the mother during her lifetime.

Dioxins, PCBs and flame retardants are some of the persitent pollutants that are stored in body fat and often detected in breast milk. Unfortunately, it is believed that infants – who are small and rapidly growing – are particularly susceptible to the chemicals' adverse effects on growth and development.

However, public health officials strongly believe that the benefits of breast milk far exceed the risks associated with pollutants in the milk. The results of this study do not change that belief.

In this small but well-designed study, 10 participants donated samples of their breast milk at one, two and three months after childbirth and when they ended breast feeding, which varied from woman to woman. Blood and milk samples were analyzed for 63 chemicals known to congregate in fat. This is the first study of its kind to sample breast milk and blood at the same time and analyze the pollutants they contain several times during nursing, say the authors.

Concentrations of many pollutants in the breast milk did not always decrease during the breast feeding phase, the researchers report. Some of these are the flame retardants (PBDEs), industrial pollutants (PCBs and dioxins) and organochlorine pesticides.

Sometimes, concentrations actually increased over the course of breast feeding. But, when so few women are studied, it is hard to know for certain if the individual patterns of pollutants in the milk are due to lifestyle factors – such as diet – that could be modified.

"The trend of the chemical concentration is mother-dependent and does not appear to be related to her initial concentration," say the authors.

The difference seem in part related to the class of chemicals. Levels of DDE (an indicator of DDT exposure) and several PCBs – all now banned – increased from month one to month three in almost all of the nine mothers tested.

Public health officials have suggested women “pump and dump” their milk to reduce infant exposure to harmful contaminants. Women were advised to pump the first milk produced – which was thought to contain the most pollutants – and throw it away instead of feeding it to the baby. If pollutant levels in the milk do not decrease during the course of breast feeding, as this new study suggests, the practice is may not be as valuable as once thought.

"The concept of pumping and discarding early milk as means of reducing infant exposure is not supported" in the study, say the authors.

This new research doesn’t change the benefits of breast milk. Breast feeding is still the best food for infants. Tighter regulations of chemicals are likely a more effective way to protect infants from contaminants than pump and dump.