Photo: National Food Institute, Technical University of Denmark

Endocrine disrupters can affect breast development

Tuesday 15 Sep 15


Ulla Hass
Emerita, Professor
National Food Institute
Studies in rats indicate that endocrine disrupters can affect breast development in humans. Their effect on breast development can however be overlooked by current methods for safety testing for endocrine disrupting effects of chemicals. These are some of the findings from a PhD project from the National Food Institute, Technical University of Denmark.

Up until now toxicological studies of chemicals that disturb the hormone system (endocrine disrupters) have mainly focused on how the chemicals can contribute to changes in the male reproductive system, e.g. low sperm count. There is however also a tendency for girls to reach puberty and to develop breasts at an earlier age. Studies have fx indicated that breast development in girls may be sensitive to endocrine disrupters.

In a PhD project at the National Food Institute, Karen Riiber Mandrup has studied the development of the reproductive system in rats that were exposed to endocrine disrupters in fetal life and through breast milk.

Female rats – that were used as a model for humans – were exposed to endocrine disrupters during pregnancy and after birth until weaning. The effects of various chemicals on female genital malformations and mammary gland development of the pups were examined. Results show that environmentally relevant chemicals – such as bisphenol A, parabens and UV-filtres – appeared to increase mammary gland growth in young females.

Effect on breast development can be overlooked

When chemicals are studied for harmful health effects, current OECD guidelines recommend that mammary glands from adult animals are examined for endocrine disrupting effects. However, Karen Riiber Mandrup’s PhD indicates that the effect on mammary gland development can be overlooked, if the studies are only carried out in adult animals.

Possible risk of effects in humans

One of the studies, which has just been published, showed increased breast development in rats that had been exposed to a mixture of environmentally relevant chemicals. A comparison of the dose the rats were exposed to with what humans are exposed to indicate a low safety margin for highly exposed humans. However, there is still a lack of scientific knowledge about the effects at lower doses.

Early breast development increases risk of cancer

Increased mammary development in the young rats can suggest similar effects in humans. It is worrying if girls who are exposed to endocrine disrupters develop breasts at a young age, as early breast development may be associated with an increased risk of developing breast cancer later in life. 

However, Karen Riiber Mandrup emphasizes that more studies are needed to examine the long-term effect of the early changes in mammary glands and also whether exposure to endocrine disrupters contribute to early breast development and/or breast cancer risk in humans.

Read more

The results have been described in Karen Riiber Mandrup’s PhD thesis: Endocrine disrupting chemicals: Effect on mammary gland development and female genital malformations (pdf).

Read more about the study of environmentally relevant chemicals’ effect on breast development in rats in the journal Reproductive Toxicology: Mixtures of environmentally relevant endocrine disrupting chemicals affect mammary gland development in female and male rats.

Also read the National Food Institute’s press release from 19 March 2015: New knowledge strengthens risk assessment of chemical cocktails in food, and read more about the institute’s research into reproductive toxicology on the institute’s website.
23 APRIL 2021