Research from VU ecologist Bérénice Collet indicates that breast milk contains chemical contaminants that can result in the feminization of boys’ reproductive systems.

What did your research show?

„In new-born babies we see that actions of androgens, the group of hormones that regulate the development of male characteristics, are extremely low in our samples. It now appears there are substances in breast milk that disrupt androgen function. Of the 199 breast milk samples I analyzed, 129 were contaminated with antiandrogen compounds." 

Where do these chemicals come from?

„Mainly from food and environmental pollution. Everyday products contain these chemicals, including cosmetics, furniture and plastic food packaging. These chemicals remain in our bodies for around a week after intake and are therefore not prohibited. However, if you use these products every day, they are present continuously and it has now been shown that these chemicals are dangerous."

What exactly does this mean for boys’ development?

„Many mechanisms that rely on those androgens are affected. Our research focuses on the relationship between androgens and cryptorchidism, the absence of one or both testes from the scrotum. This problem can be resolved via an operation in the first weeks of life. But if this is not addressed or is addressed too late, it can result in impaired germ cell development."

„Our hypothesis is also that reduced androgen function can result in penis length reduction, breast development and reduced libido."

„Reproductive cells, which later develop to become spermatozoa, remain too long in the abdominal cavity where the temperature is too high. This slows or entirely inhibits the development into sperm. Our hypothesis is also that reduced androgen function can result in penis length reduction, breast development and reduced libido."

Many research studies into breast milk have already been conducted. How does this research differ?

„The disadvantage is that previous research studies focused on one specific substance or category of chemicals. However, chemicals respond very differently in certain combinations. We developed a new method for this in which we extracted all the substances present in breast milk to enable analysis of the combined effect."

„I don’t want to discourage mothers from breastfeeding."

Undescended testis is a newborn deformity, therefore, why is that relevant to study breast milk as it is only given after birth?

„The composition of breast milk is similar to umbilical cord blood. Now that breast milk has been shown to be contaminated, our hypothesis is that unborn babies also absorb antiandrogen substances via umbilical cord blood. This blood is less easy to obtain, which is why we opted for breast milk. Should our hypothesis be correct, this would mean that children don’t only often consume antiandrogen substances for a year after birth, but also before they’re born."

The outcomes are harsh considering that breast milk is often seen as the best nourishment for babies.

„I don’t want to discourage mothers from breastfeeding. This also sometimes makes this research difficult to defend. However, I think it’s important to know what you’re feeding your child. As yet, we’re unable to tell women what they shouldn’t eat and which skincare products they should avoid. Combinations of chemicals can in some cases disrupt androgen function and in other cases these are harmless. So we need to do much more research, but I hope we’ll be able to produce guidelines for mothers and their babies in the future."