Endocrine Disruptor: Should we be wary of soybean oil?

According to the World Health Organisation (WHO), the term "endocrine disruptor" refers to "a substance or a mixture of substances that alter the functions of the endocrine system and thereby induce harmful effects in an intact organism, its offspring, or within (sub)populations". Put simply, it is a family of compounds capable ofinteracting with the hormonal system, thereby affecting various functions of the body (metabolism, nervous system, reproductive functions...).

Endocrine disruptors can alter the hormonal system at various levels. They can interact with the synthesis, transport, mode of action, or even the degradation of hormones. Thus, the physiological changes brought about by endocrine disruptors are due to their indirect effects. The mechanisms of action of endocrine disruptors are quite varied but, most often, these substances alter the natural production of intrinsic hormones, mimic the action of these hormones by substituting for them, or prevent their action by attaching to the receptors with which they usually interact.

The origins of endocrine disruptors are diverse and the sources of exposure are numerous. Indeed, these molecules can be present in everyday objects such as household products, cosmetics, agri-food products... Endocrine disruptors are also found in the environment due to frequent contaminations of various mediums, such as water, sediments, soils, or even the air we breathe.

Note : It is important to clarify that many compounds labelled as endocrine disruptors are most often only suspected of being so. Indeed, it is very difficult to demonstrate that a substance interacts with the hormonal system, which explains why there are very few proven endocrine disruptors to date.

Soybean oil presents itself as a golden liquid, easily absorbed by the skin and lightly scented. It is generally obtained by cold pressing soybean seeds, and is found in various cosmetic treatments: creams and lotions, body care products, skin care products, hair products, tonics and makeup products. Despite the benefits it brings to the skin, it is often singled out and labelled as an "endocrine disruptor".

This is due to the fact that soybeans are rich in isoflavones, molecules found in plants but which have an oestrogenic or anti-oestrogenic activity in humans. Indeed, isoflavones belong to the family of phytoestrogens, compounds that have a molecular structure similar to that of oestradiol, which allows them to bind to receptors specific to these hormones. In doing so, soy is likely to interact with the hormonal system. It therefore fits the definition of an endocrine disruptor as it performs the action of a feminising hormone. This is why health authorities recommend not giving soy to children under 3 years old and advise pregnant and/or breastfeeding women to do the same.

However, when it comes to soybean vegetable oil, it is more challenging to draw conclusions because its isoflavone content is minimal, rendering its oestrogenic power almost non-existent. Indeed, during the extraction of oil from soybean seeds, phytoestrogens tend to remain in the beans and do not transfer into the oil. It should be noted, however, that depending on the quality of the soybean seeds and the method used to extract the oil, the quantity of isoflavones in the oil can vary.

At present, the potential of soybean oil to act as an endocrine disruptor when applied topically is still being debated within the scientific community. Therefore, while soybean vegetable oil is not officially considered an endocrine disruptor, it is advisable to remain cautious and wait for more studies to be conducted before drawing conclusions.

As a precautionary principle, the cosmetic use of pure soybean oil is contraindicated for pregnant women, breastfeeding mothers and children. As mentioned earlier, the potential of soybean oil to act as an endocrine disruptor has not been sufficiently studied.

More research has been conducted on the effects of phytoestrogens alone. It has been demonstrated that these compounds possess moisturising properties and slow down the skin ageing mechanisms. Indeed, it appears that phytoestrogens stimulate the production of collagen, as well as hyaluronic acid, a constituent of the dermis contributing to the firmness and tone of the skin. However, other scientists are less enthusiastic about phytoestrogens and report negative effects on fertility, due to the disruption of oestrogen activity.

Key Point : It is important to note that these studies pertain to phytoestrogens and not soybean oil, which only contains traces of these compounds. Thus, they only provide indirect evidence.

• EBOSHIDA A. & al. Effects of isoflavone supplement on healthy women. Biofactors (2000).

• HARRATH A. H. & co. Phytoestrogens and their impacts. European Journal of Pharmacology (2014).

• PLANCHENAULT N. & al. Soy foods: consumption in France, nutritional qualities and recent scientific data on health. Oilseeds & fats, Crops and lipids (2016).