Over the past few years, interest in health research has increased, making improved health a global goal for 2030. The purpose of such research is to ensure healthy lives and promote wellbeing across individuals of all ages. It has been shown that nutrition plays a key role in the prevention of some chronic diseases such as obesity, cardiovascular disease, diabetes, and cancer. One of the aspects that characterises a healthy diet is a high intake of vegetables and fruits, as both are flavonoid-rich foods. Flavonoids are one of the main subclasses of dietary polyphenols and possess strong antioxidant activity and anti-carcinogenic properties. Moreover, some population-based studies have described a relationship between cancer risk and dietary flavonoid intake.
1. Introduction
Cancer is among the diseases that have the greatest impact on society
[1]. Even though its incidence has increased over the years, its mortality has decreased because of advances in treatment
[2]. However, efforts to improve cancer prevention are needed. The aetiology of cancer is multifactorial, involving both environmental and genetic factors
[3]. Diet is one of the lifestyle factors that affect cancer incidence and mortality
[4]. Recently, several studies have reported that diets based on high levels of vegetables and fruits are strongly associated with a significant reduction in cancer risk
[5,6][5][6].
Furthermore, there are some bioactive compounds in foods that have potential health benefits, such as flavonoids, carotenoids, stilbenes, lignans, and phenolic acids
[7,8][7][8]. Flavonoids are a large group of phenolic compounds and are usually involved in protection against harsh environmental conditions, UV radiation, and microorganism attacks in plants
[9,10][9][10]. Because of their potent antioxidant activity against oxidative stress, the interest in flavonoids has recently increased
[11]. In vitro and in vivo studies have demonstrated that they have anti-carcinogenic properties against different types of cancers
[5,12][5][12]. Moreover, many population-based studies have described an association between dietary flavonoids and cancer risk
[13,14][13][14]. Hence, the goal of this review is to perform an updated evaluation of the association between the risk of different types of cancers and dietary flavonoids, as well as the intake of each flavonoid subclass.
2. Dietary Flavonoids
Flavonoids are widely spread in different foods and beverages (such wine and tea), but the sources with the highest levels are fruits and vegetables
[10]. Among the fruits (
Table 1), the highest levels of flavonoids are found in berries, such as black elderberry (1358.66 mg/100 g) and black chokeberry (1012.98 mg/100 g)
[18,19][15][16]. In the drupes group, some fruits such as plum and sweet cherry have higher levels of flavonoids than the rest of the group, 101.67 mg/100 g and 185.05 mg/100 g, respectively
[20,21][17][18]. In the pomes group, apple has the level (56.35 mg/100 g)
[21,22][18][19]. Furthermore, tropical fruits have a very low flavonoid content
[23][20]. Depending on the type of fruit, the main flavonoid subclass groups vary: anthocyanins predominate in berries, and flavanols predominate in pomes, tropical fruits, and drupes (except in sweet cherry).
Table 1. Flavonoid contents of fruits (mg/100 g food). Data collected from Phenol Explorer
[24][21].
Fruits |
ANT |
DYC |
FVA |
FVO |
Total |
Berries |
Table 2. Flavonoid contents of vegetables (mg/100 g food)
[24][21].
Vegetables |
ANT |
CHA |
FVA |
FNE |
FVE |
FVO |
Total |
Regarding cereals (
Table 4), some such as barley, buckwheat, and common wheat contain average levels of flavonoids (35.2 mg/100 g, 37.04 mg/100 g, and 77.4 mg/100 g, respectively). However, it is important to note that the highest levels are found in whole grains, and levels are greatly reduced when grains are heat treated or refined
[30,31][27][28].
Table 4. Flavonoid contents of cereals (mg/100 g food)
[24][21].
Cereals |
FVA |
FVE |
FVO |
Cocoa | Total |
FVA |
FVO |
Total |
Cabbages |
Cereals |
Aestivalis grape |
79.74 |
Broccoli |
- | - |
Cocoa |
- |
1.7 |
81.44 |
- |
- |
- |
0.5 |
- | - |
27.8 |
27.8 |
3.81 |
0.06 |
9.3 |
Barley, whole grain flour |
35.2 |
- |
- |
35.2 |
American cranberry |
49.89 |
Fruit Vegetables | - |
- |
Chocolate dark |
212.36 |
25 |
237.36 |
43.84 |
93.73 |
Cashew nut |
- |
1.1 |
- |
- |
- |
- |
1.1 |
Chocolate milk |
19.22 |
- |
19.22 |
Black chokeberry |
878.11 |
- |
Avocado |
-- |
Cocoa powder |
511.62 |
- |
511.62 |