Flavonoids have demonstrated antioxidant, antiviral, anticancer, and anti-inflammatory effects. Flavonoid type, bioavailability, and possible method of action determine these biological actions. These low-cost pharmaceutical components have significant biological activities and are beneficial for several chronic disorders, including cancer.
1. Introduction
A number of studies have pointed to the importance of a plant-based diet in warding off conditions that can lead to cancer
[1]. Vegetables contain a number of bioactive components, including phenolic compounds, carotenoids, and, most notably, flavonoids, which may contribute to the plant-based diet’s health advantages. The amount of research focused on exploring flavonoids thoroughly has risen significantly in the most recent years as a result of these potential uses.
As a class of phenolic chemicals generated by plants, flavonoids are classified as secondary metabolites. They can be found in a wide variety of photosynthetic species and are particularly prevalent in meals and beverages derived from plants, though their precise makeup varies greatly. Two benzene rings (A and B) are joined to the heterocyclic pyranic ring (C) to form the chemical structure’s 15-carbon skeleton
[2]. There are many different types of flavonoids, and they may be broken down into several different classes: anthocyanins, flavones, flavonols, chalcones, isoflavones, flavanones, flavanonols, and flavanols
[3]. This difference is due to the degree of unsaturation of the flavone ring and the oxidation of the carbonaceous ring (
Figure 1), the key skeletons of the flavonoid.
It is challenging to establish epidemiologic correlations regarding the impact of flavonoids on human health versus disease due to the difficulty of estimating dietary intake due to the large quantitative and qualitative heterogeneity of flavonoids in a variety of vegetables and fruits. Flavonoids have been a part of the human diet in almost all geographic regions
[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].
2. Overview of Dietary Flavonoids
Flavonoids are widely distributed in foods and beverages of plant origin, such as fruits, vegetables, tea, cocoa and wine. A large amount of literature exists regarding flavonoid content in foodstuffs, which is summarized below (Table 1).
A number of studies have summarized the vast body of research on the bioavailability and absorption of flavonoids
[31][32][33]. The molecular weight, glycosylation, and esterification of flavonoids, among other things, can impact their bioavailability, leading to some doubt about their actual levels of bioavailability as well as absorption in the human body
[33]. Other studies also provide an in-depth account of how flavonoids are metabolized after ingestion
[32][34]. The largest levels of flavonoids are found in fruits and vegetables
[35]. Flavonoids are found in a variety of foodstuffs and beverages, although they are most prevalent in fruits and vegetables. Depending on the kind of fruit, the primary subclasses of flavonoids vary: anthocyanins prevail in berries, whereas flavanols predominate in pome fruits, tropical fruits, and drupes.
Some cereals (barley, buckwheat, and common wheat) have average flavonoid levels. However, it is vital to remember that whole grains contain the highest quantities when raw, and levels are dramatically reduced when grains are treated with heat or refined for further use
[36][37]. Flavonoid-rich foods include cocoa and its derivatives. Flavanols are the most abundant flavonoids in these foods, with cocoa containing the maximum amount of flavanols
[38][39]. Tea infusions, notably black and green tea, have the highest quantities of flavonoids in non-alcoholic beverages, primarily flavanols
[40][41][42]. Fruit juices, in particular apple juice, orange juice, grapefruit juice, and lemon juice, are the second most flavonoid-rich beverages
[43]. Flavanones are the primary flavonoids found in citrus and grapefruit juices
[44][45]. Food stuff and drinks rich in flavonoids (
Table 2) are summarized below
[46].
Besides influencing mammalian metabolism, flavonoids have been linked to a wide range of anti-inflammatory, antiviral, antiproliferative, and anticarcinogenic properties
[47]. Certain pathological illnesses, such as gastric and duodenal ulcers, allergies, vascular fragility, and viral and bacterial infections, have gained a lot of attention because of the beneficial effects flavonoids have as antioxidants in preventing human diseases, including cancer and cardiovascular disease
[48]. In general, flavonoids have been discovered to exhibit a variety of pharmacological properties
[47]; these include antioxidant, antiallergic, antiinflammatory, antidiabetic, hepato- and gastro-protective, antiviral, and antineoplastic activity.
3. Effects of Flavonoids in Chemoprevention and Chemotherapy
Flavonoids are effective anti-inflammatories as well as potent antioxidants that combat free radicals, which are related in a crucial way to many degenerative chronic diseases and are responsible for a wide range of biological processes (
Figure 2). An increase in free radicals under pathological conditions not only causes cellular aging and death but also promotes carcinogenesis by causing damage to various molecule types, including nucleic acids, proteins, and lipids
[4].