Breast milk is best for new babies but it's not the 'pure' food we thought

A Harvard University researcher last week suggested western women stop breastfeeding after a couple of months to reduce the risk of passing potentially harmful toxins on to their infants via breast milk.

But while babies may receive chemicals and allergens in breast milk, it doesn’t mean breastfeeding is unsafe. For most women, breast milk is the best food for new babies.

Benefits of breast milk

Breastfeeding is the natural way to feed human infants. After all, infant formula is made with cow’s milk, and our babies are not little cows. The World Health Organization (WHO) recommends:

Exclusive breastfeeding … up to six months of age, with continued breastfeeding along with appropriate complementary foods up to two years of age or beyond.

These guidelines are estimated to save up to 800,000 lives a year in low-income, developing countries.

The first breast milk, known as colostrum, contains antibodies, live immune cells and anti-bacterial proteins and is very important for the new baby’s immune system.

When a baby is born, the immune system is immature and the baby is at risk of contracting infections, especially respiratory viral infections. Breastfeeding reduces the risk of infections in early life and may reduce the risk of long-term diseases such as asthma, excess weight and obesity, and type 2 diabetes.

There is increasing evidence that vaccinating pregnant women against infections that threaten infant’s lives, such as whooping cough and influenza, may be the best way of protecting very young infants against these diseases. The precise mechanism underlying this protection is not known, but the immunological benefits of colostrum are likely to be involved.

But while the protection breastfeeding confers on infants in low-income developing countries against death from lower respiratory illnesses is indisputable, the same situation does not exist in high-income developed countries.

Some women are not able to breast feed, for reasons that are beyond the scope of this article, and the current focus on breastfeeding in countries such as Australia can leave these women feeling guilty that they have “failed” their babies.

Is breast always best?

Breast milk is produced by the mother’s body and, as such, is subject to the condition of her body. Infections such as HIV can be passed to infants via breast milk.

However, the WHO breastfeeding guidelines suggest that that HIV-infected women should breast feed, provided that they are on adequate anti-retroviral treatment. Indeed, substantial progress has been made in high-prevalence countries such as South Africa in reducing infant HIV infection while allowing the benefits of breastfeeding.

There is no doubt that breast milk is also likely to contain the same range of external or “xenobiotic” substances that exist in the mother’s body, including many prescribed and illicit drugs and environmental chemicals.

We used to think that that the placenta protected the developing fetus from maternal exposures and that breast milk was a “pure” and uncontaminated substance. Unfortunately neither of these beliefs is true. For practical purposes, the developing fetus is exposed to what the mother is exposed to and the breastfeeding infant is exposed to contaminants in the mother’s body.

Chemicals and allergens

Since the “chemical revolution” of the mid-to-late 20th century, hundreds of thousands of chemicals have been introduced into use with minimal to no testing to demonstrate their safety.

The Centres for Disease Control and Protection in the United States monitor the population for 212 environmental chemicals and report that almost all Americans have these chemicals in their body; many of which, especially those that are soluble in fat, are likely to pass into breast milk.

There is no such population biomonitoring program in Australia. Many of the environmental chemicals have activities that mimic hormones and are collectively known as endocrine-disrupting chemicals.

One of the most controversial recently is bisphenol-A, which has been banned from products designed for babies in several countries but not in Australia.

A new report from a group of Danish and American researchers investigated levels of water- and stain-proofing chemicals, known as perfluorinated alkylate substances, or PFASs, in children from the Faroe Islands. The babies who were exclusively breastfed had levels 20-30% higher, which gradually fell after weaning.

While data on this class of chemicals is new, the problem is not. Breastfed infants receive “doses” of many chemicals from their mother, including flame retardants, pesticides, plasticizers, and many long-lived persistent chemicals that are no longer in use.

It is not only chemicals that can pass into breast milk. Food proteins are also likely to be present and can increase the risk of food allergy. The infant feeding guidelines of the Australasian Society of Clinical Immunology and Allergy encourages breastfeeding but also state that early introduction of solid foods, around four to six months of age, may help prevent food allergy.

Benefits and risks

Does the fact that babies receive chemicals and allergens in breast milk mean that breastfeeding is unsafe?

No, it clearly does not. While the chemicals in breast milk can be associated with adverse health effects, there is not a good understanding of what levels of such chemicals are unsafe or when, if ever, the potential adverse effects outweigh the benefits of breastfeeding. Balancing the pros and cons of breastfeeding would not be a trivial undertaking and, to my knowledge, has not been attempted.

There is a relatively new methodology, known as integrated environmental health impact assessment that could be used to tackle this complex issue. This methodology is designed to incorporate the complexities of real world problems and to include views of stakeholders in framing the assessment scenario and in interpreting the results.

In the case of breastfeeding, this assessment would need to include views from a wide cross section of health care professionals, toxicologists and the general public. The results of such assessments would also be specific to the location in which they were undertaken, with potentially different conclusions reached in low-income and high-income countries.

The bottom line is that breast milk is the best food for new babies but that it is not the “pure” food it was assumed to be. For the vast majority of women and babies, breastfeeding, provided that it is possible, is best.

At this stage, it is not possible to provide accurate advice to Australian women about when, if ever, breastfeeding should be limited because of increased risks posed by chemical levels in the milk. Further research in this area is definitely needed.

Peter Sly does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.