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Flavonoids are an extremely diverse family of plant compounds, which is why their effects on the human body and cells are extensive. In general, it can be said that their antioxidant and anti-inflammatory properties can help prevent or support the treatment of certain diseases. Science examines the protective role of flavonoids against diseases caused by chronic inflammation or associated with inflammation through long-term monitoring of patients and is supported by measurements using molecular biological methods and animal experiments.
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 a high daily intake of a minimum of 500 mg of flavonoids.
The effect of flavonoids on the outcome of cancer deaths was more spectacular:
500-1000 mg of flavonoids per day reduced the fatal risk by 15-20% compared to the small dose (173 mg per day).
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) with either fisetin or cabazitaxel chemotherapeutic agents had only slight improvement. However, when the two were combined, they significantly increased the average survival of the mice and decreased the tumor growth rate.
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 considerable, it did not totally cure the animals. However, multiple other studies suggest that, similar to fisetin, a considerably more potent anti-cancer effect could be reached when combined with chemotherapy.
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 the technical term: inducing apoptosis.
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In the first half of 2020, two studies were published in prestigious journals exploring the link between flavonoid consumption and the development of Alzheimer’s disease. One study monitored participants with an average age of 81 years for 14 years, and the other followed subjects with an average age of 59 years for 20 years.
Studies independently showed that those who took higher doses of flavonoids had a much lower risk of developing Alzheimer’s disease and associated dementia.
According to the authors, the important source of flavonoids contributing to the prevention, such as kaempferol, myricetin, and anthocyanins e.g. kale, broccoli, apples, green tea, and berries, therefore, the consumption of flavonoid-rich meals is recommended.
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In mice asthma models, the flavonoid called chrysin was able to achieve a similar effect to that of dexamethasone (the anti-asthma steroid) by reducing bronchial inflammation and overactive immunological response, and by lowering IgE antibody levels in the blood.
In mouse models, flavonoids such as galangin or quercetin (extracted from onions) were also effective, as was the case with other research groups.
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Every day our body is exposed to many stressors. A part of the environmental stress (e.g., air pollution, chemicals) and mental stress are manifested as free radicals within the body. Free radicals are highly reactive and can bind to nearby cell constituents – lipids, proteins, and other important biomolecules, thus impairing their proper functions.
A healthy body is prepared for (resistant to) oxidative stress and the neutralization of harmful free radicals since they are also produced in the body as byproducts of our metabolism. However, the extra amount of stress and harmful habits associated with modern living (smoking, regular alcohol consumption) can challenge the so-called redox balance, but for some diseases or in old age, we may not be able to respond effectively.
Many vitamins can help fight oxidative stress, as they trap free radicals as antioxidants and neutralize their destructive effects. The effect of vitamins is further enhanced by flavonoid-type antioxidants, which are found in plants.
The biological effects of flavonoids were first discovered by Hungarian Nobel laureate Albert Szent-Györgyi and his colleagues. When scurvy patients were treated with vitamin C, more efficient and faster healing happened when the patients were also given yellow powder extracted from Hungarian red pepper or lemon juice. The yellow powder was named the flavonoid fraction (the yellow color is ‘flavus’ in Latin), and the polyphenol-type components identified in it were named flavonoids.
Flavonoids have been the subject of intensive research, since. In general, flavonoids are effective antioxidants on their own and enhance the effects of vitamins. There can be up to 6,000 different flavonoids, all of which have varying degrees of antioxidant capacity, but they can also have other functions depending on their structure, can bind to a number of enzymes, and affect our metabolism.
Within the body, the rise of local concentration of free radicals may lead to the onset of inflammatory processes, if persists for a long time, chronic inflammation may occur. Prolonged nerve inflammation can be a trigger of many serious diseases and can contribute to the development of cancer, Alzheimer’s or Parkinson’s disease, insulin resistance and diabetes, asthma, and certain cardiovascular diseases.
Due to their general antioxidant and anti-inflammatory effects, flavonoids can help prevent or stop the development of chronic inflammatory conditions, and some of their types may be suitable to support the treatment of diseases.