According to a grouped study published in Denmark, 2019, in which the dietary and other habits of 56,000 participants at the age of 52-60 years were monitored for 23 years, the death rate of patients was approximately 15% lower if - instead of the 173 mg of flavonoids intake per day, rather - 500 mg of flavonoids was administered. The effect of flavonoids was more spectacular concerning the outcome the deaths of cancer: the at least 500-1000 mg of flavonoids per day meant 15-20% risk reduction as compared to the low (173 mg daily) dose.
The protective effect of flavonoids was higher among smokers or regular drinkers considering all causes of death, which means that the destructive effects of these harmful habits may also be offset by high daily intake of a minimum of 500 mg of flavonoids
The anti-cancer effects of flavonoids have been demonstrated in several animal experiments. The most prominent effect is linked to a flavonoid called fisetin. Treating prostate xenograft tumors (human tumor cells implanted in mice) both fisetin and cabazitaxel chemotherapeutic agent by itself had only slight improvement, but when the two were combined, they significantly increased the average survival of the mice, and the tumor growth decreased. In other studies, a flavonoid called quercetin slowed down the growth of liver, breast, and colon-type xenograft tumors, and increased the average survival of the animals. Although the effect of quercetin alone was significant, it did not completely cure the animals, but several other publications suggest that a much more pronounced anti-cancer effect could be achieved in combination with chemotherapy, just as with fisetin.
Based on experiments on isolated cancer cells, flavonoids may exert their anti-cancer effects through other mechanisms in addition to their antioxidant and anti-inflammatory effects. Depending on the flavonoid type they may intervene in the survival, proliferation, and migration of cancer cells and signaling pathways responsible for the formation of new veins in such a manner that they inhibit the activity of cancer cells, or trigger the ‘self-destruct’ program of the malignant cells, with technical term: inducing apoptosis.
- Flavonoid intake is associated with lower mortality in the Danish Diet Cancer and Health Cohort. Nat Commun. 2019; 10: 3651.
- Fisetin Enhances Chemotherapeutic Effect of Cabazitaxel against Human Prostate Cancer Cells. Mol Cancer Ther. 2016; 15(12):2863-2874.
- Investigation of the anti-cancer effect of quercetin on HepG2 cells in vivo. PLoS One. 2017; 12(3):e0172838.
- Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncol Rep. 2017; 38(2):819-828.
- Quercetin in Cancer Treatment, Alone or in Combination with Conventional Therapeutics? Curr Med Chem. 2015; 22(26):3025-39.
- Flavonoid-Based Cancer Therapy: An Updated Review. Anticancer Agents Med Chem. 2020; doi: 10.2174/1871520620666200423071759.