4. Geographical differences in total flavonoid intake and their food sources

The intake of flavonoids varies greatly by country/geographical region due to different dietary patterns; although differences in the flavonoid classes included, the dietary assessment methods, the food composition database use, and the method of expression (glycoses vs aglycones) applied complicate these comparisons. Table 1 summarizes the most important descriptive studies assessing flavonoid intakes in different countries/regions. The mean intake of flavonoids worldwide ranges between 150 and 600mg/day expressed as aglycones without thearubigins [20–26]. Taking into account thearubigins, the flavonoid intake could increase by a negligible amount in populations with low black tea intake, but would double the intake in black tea-consuming countries, such as the UK (from ∼500 to >1000mg/day) [27].

Europe is the continent with the most number of studies assessing the intake of total flavonoids, and therefore, it is possible to describe their intake quite accurately. Moreover, studies like the European Prospective Investigation into Cancer and Nutrition (EPIC) study allow us to compare the intake in 10 European countries using the same methodology [21, 26]. In Europe, an increasing south-to-north gradient is usually observed [26]. Despite the high intake of fruits, vegetables, and red wine in Mediterranean (MED) countries, the intake of total flavonoids in these countries (250–400mg/day) is lower than in non-MED countries (350–600 mg/day), even without taking into account thearubigins. This is due to the much higher consumption of tea in non-MED compared to MED countries. These differences would be larger if thearubigins were also included [27]. The highest total flavonoid intake in Europe is in the UK, due to the traditional tea culture [21, 26]. Eastern European countries, such as Poland, also have a high intake of total flavonoids (∼600mg/day), related to their high tea consumption [32, 40]. Southern regions of France are considered as a MED region, while northern regions as a non-MED region; therefore, France has an intermediate intake of total flavonoids, with the main food sources being fruit, tea, and red wine (a combination of food sources from MED and non-MED countries) [33]. In Scandinavian countries with a low consumption of tea, such as Finland, the intake of total flavonoids (200–250mg/day) is lower than MED countries, since the consumption of fruit is lower as well [31].

In Australia, there are various studies describing the intake of total flavonoids [20, 28, 29]. As a high tea-consuming country, Australia has a high intake of total flavonoids (650–700mg/day), including thearubigins. In the three Australian populations documented, black tea contributes to at least 75% of total polyphenols.

In America, several studies have estimated the intake of total flavonoids, especially in the US [22, 34–36, 41], since the USDA databases were developed there [13–15]. In the US, the mean intake of total flavonoids varies from 250 to 400mg/day, including proanthocyanidins and thearubigins [22, 34–36, 41]. Although the consumption of tea is not very high, tea is still the main food source of total flavonoids in the US, probably due to a low consumption of fruits



Study NNS95 Calcium Intake Fracture

Outcome Extension Study The Blue Mountains

EPIC

 Eye

 Australia

MED

Non-MED

> PREDIMED

TOSCA.IT SUVIMAX FINDIET 2002

HAPIEE Polish National Multicenter

Health Survey

NIH-AARP NHS I & NHS II & HPFS

NHANES Mexican Teachers' Cohort

Health Survey-São

Cross-sectional

 study

 China

 3317

 SemiQ-FFQ

 USDA

 Aglycones

 225\*

Flavanols\*\*

 Soy, pome fruit [24]

 Paulo

 Brazil

 1103

 24-HDR

 PE

US

 US US

 Mexico

 106,466

 FFQ

 PE

 8809

 24HDR

 USDA

 Aglycones Aglycones

Glycosides

Glycosides

 54.6\*

Flavanones

 Citrus fruit,

[37]

beans

 235\*

 140\*

 264

 156,957

 FFQ

 USDA

 Aglycones

 391

 491,840

 FFQ

 USDA

 Aglycones

 203\*§

Flavanols\*\*

PA Flavanols\*\*

PA

Fruit and

[23]

orange juice

 Tea

Tea

[35]

[20, 36]

 Tea

[34]

Finland

Poland

Poland

 6661

 24-HDR

 USDA, PE

 Aglycones Glycosides

 403\*

 524.6

 10,477

 FFQ

 PE

 2007

 24-HDR

 Own database

 Aglycones Aglycones

 898\*

 209\*

PA Flavanols\*\*

Flavanols\*\*

 Tea, apples

 [33]

 Tea, cocoa

 [32]

Berries, fruit

 [31]

Spain

Italy

France

 4942

 6 24-HDR

 PE

 2573

 FFQ

 USDA

 Aglycones Aglycones

Glycosides

 505\*

 436\*

 364

 7200

 FFQ

 PE

 36,037

 24-HDR

 USDA, PE

PE USDA, PE

PE

Glycosides

Glycosides

 443

 522\*

 Aglycones

 374\*

Glycosides

 449\*

 Aglycones

 370\*

 79

 3 4-WFR

 USDA

 Aglycones

 683

Flavanols\*\*

PA PA PA PA PA PA PA

Fruit, tea, red

[17]

wine

Fruit

[30]

Fruit

[27]

Tea

[26]

Fruit

[21]

Fruit

[26]

Fruit

[21]

 Black tea

 [29]

376 Flavonoids - From Biosynthesis to Human Health

Age-Related

Country

Australia

Australia

 1136

 SemiQ-FFQ

 USDA

 Aglycones

 696

 17,326

 24-HDR

 USDA

 Aglycones

 225§

 Population

Dietary

Aglycones

glycosides

 vs.

Total flavonoid

Major class

Main food

contributor

Flavanols\*\*

Flavanols\*\*

 Black tea

 [28]

 Black tea

 [20]

sources

 References

intake (mg/day)

assessment

 FCDB cyanidins; SemiQ-FFQ=semi-quantitative FFQ; FFQ= food frequency questionnaire; FCDB= food composition database.

\*Without thearubigins.

§Without proanthocyanidins.

\*\*Flavanols is a combination of flavan-3-ol monomers and flavanol-derived compounds.

Table 1. Intake of total flavonoids (mg/day) in different countries/regions. and vegetables. In the US, some differences in the total flavonoid intake among ethnicities have been observed [22, 36]. Non-Hispanic whites have the highest intake of flavonoids (>300mg/day), whereas non-Hispanic blacks, Mexican Americans, and other ethnicities consume approximately 200mg/day. Data on other countries in America is very limited, and to the best of our knowledge, Brazil [37] and Mexico [23] are the only other countries with available data. The intake of total flavonoids is around 150 and 50mg/day in Mexico and Brazil, respectively. These are the countries with the lowest intake of total flavonoids that have been published worldwide. Although, the studies in these countries did not take thearubigins into account, the contribution of thearubigins to total flavonoids is insignificant because Brazilians and Mexicans rarely drink tea. The main food source of total flavonoids is citrus juices, followed by fruit in Mexico and beans in Brazil [23, 37]. In these Latin-American countries, a potential relevant underestimation of total flavonoids cannot be ruled out because of missing food composition data on some tropical foods, such as fruits and vegetables (e.g., mamey, zapote, papaya, sweet potato, nopal, guava, jicama, and prickly pears) that are frequently consumed in their diets and may be good sources of flavonoids.

In Asian countries, very little complete data are available, as there is only data for East Asian countries (such as China [24, 38] and South Korea [25]). The total flavonoid intake in China ranges from 65mg/day without proanthocyanidins [38] to 225mg/day with proanthocyanidins [24]. In both studies, thearubigins are not included, but Chinese people drink green tea, but not black tea. Thearubigins are formed during the fermentation of green tea to black tea. In South Korea, the intake of total flavonoids is slightly higher than in China (320mg/day) [25]. In East Asian countries, soy and its derived products (the main food sources of isoflavones) are one of the most important contributors to total flavonoids, although proanthocyanidins and flavan-3-ol monomers are the most abundant flavonoids in South Korea and China, respectively. In Japan, China, and South Korea, there are many studies focusing on isoflavones, due to their potential phytoestrogenic effects [42], but not on total flavonoids. In the Middle East, a recent study in Iran has been conducted showing a mean intake of 1650mg/day [39]. This is the highest mean of total flavonoid intake worldwide. This high amount is because of the elevated consumption of black tea in these Middle East populations.

In summary, there is a high heterogeneity between countries in total flavonoid intake. The highest intake is in Iran [39], followed by the UK (>1000mg/day) [27] and the lowest intake is in Brazil and Mexico (<150mg/day) [23, 37]. The populations with a higher intake of total flavonoids are those with a high consumption of tea, especially black tea. In this case, the main contributor to total flavonoids is thearubigins, and this may be partially explained due to the inaccurate measurement of thearubigin content in black tea [19]. Populations with a lower intake of total flavonoids are those with a low consumption of tea. In these cases, the main food sources are fruit and proanthocyanidins become the main contributor to total flavonoids. In East Asia, isoflavones are also important contributors to total flavonoids due to the high consumption of soy-derived products. Further studies are warranted to estimate the intake of total flavonoids in other regions of the world with little available data, such as Latin America, Africa, and Middle East. More research on the content of flavonoids in food is also needed in order to improve the existent food composition data, adding new foods (e.g., tropical foods) and refining the thearubigin data.
