Quercetin, which is a phytoestrogen, has been found both to inhibit and promote breast cancer cell growth depending on a variety of factors. Now a new study has reported that quercetin acts against cancer cells by inhibiting insulin receptor signaling, which in turn reduces cancer cell proliferation.

Quercetin supplements should be avoided

There is some evidence that the impact of flavonoids such as quercetin on breast cancer cells depends on the dosage, with low or high doses potentially stimulating breast cancer cell growth in some cases. When flavonoids are consumed as part of food, they are combined with other micronutrients that can act synergistically with them against breast cancer. Consuming flavonoid-rich foods is safe and could help prevent breast cancer or its recurrence. On the other hand, safe and effective dosages of flavonoid supplements have not been established and they have the potential to increase breast cancer risk or reduce the effectiveness of treatment.

A number of studies have reported that quercetin can kill breast cancer cells and even enhance the treatment effects of radiation treatment and chemotherapy. However, several studies have reported that quercetin can promote cancer. For example, one study reported that quercetin contributed to the growth of estrogen-induced mammary tumors, but only once the tumors were established in female rats. In other words, supplemental quercetin did not induce tumor initiation but did contribute to tumor growth.

On the other hand, population studies have consistently found that high-flavonol diets are associated with reduced breast cancer risk. A number of foods with significant quercetin content have been found to be associated with reduced breast cancer risk.

Latest research finds quercetin inhibits insulin receptor signaling

The study referenced at the beginning of this news article was designed to investigate the mechanism of action by which quercetin inhibits insulin receptor (IR) signaling. Previous studies have established that quercetin inhibits breast cancer cell growth in part by inhibiting activation of IR signaling. However, the mechanism has not been established. In the study, the authors demonstrate that quercetin interferes with specific IR interactions. As a result, insulin-stimulated glucose uptake is inhibited due to decreased cell membrane translocation of glucose transporter 4 (GLUT4). This, in turn, impairs cancer cell proliferation.

The authors also tested the effects of quercetin in an animal model of cancer. Quercetin inhibited tumor growth in this model, suggesting that quercetin might be useful in the treatment of cancers, according to the authors.