Dietary sources of flavonoids in Western societies include onions (flavonols); cocoa (proanthocyanidins); tea, apples, and red wine (flavonols and catechins); citrus fruit (flavanones); berries and cherries (anthocyanidins); and soy (isoflavones).

Here’s how far we’ve come.

1930s

• Hungarian scientists identify “vitamin P” (for permeability) from lemon peels.
• It reduces capillary permeability and treats purpura (purple discolorations of the skin).
• “Vitamin P” (or citrin) is found to be a mixture of the flavonoids hesperidin and eriodictyol glucoside.

1950s

• Flavonoids lose their vitamin status.

1970s

• Suspected of increasing the risk of cancer (mainly, quercetin).

1980s

• Their tainted reputation is repaired and are considered anti-cancer substances.
• A Dutch researcher reports a protective effect of several flavonols — quercetin, kaempferol, and myricitin — against death due to coronary heart disease.

1990s

• Protection from stroke reported.

2000s

• Doubt is cast on the protective effects of flavonoids.
• Conflicting study results might be due to differences in overall dietary flavonoid intake or differences in specific flavonoid-containing foods.

The bottom line?
According to Profs. Johanna Geleijnse and Peter Hollman from Wageningen University in the Netherlands, most studies focus on flavonoid-rich products rather than the effect of specific flavonoids alone.

This makes it difficult to determine whether the heart benefits of, for example, chocolate and cocoa, are due to their rich mixture of flavonoids or to other substances that act on the cardiovascular system, such as theobromine, tryptophan, caffeine, and minerals such as potassium and magnesium.

For now, it’s clear that flavonoid-rich foods have a beneficial effect on blood vessels, blood pressure, and cholesterol. So, although we don’t know the best dose, it’s reasonable to include sources of flavonoids as part of a healthy diet.

But, you’re probably doing that already.

7/9/08 16:18 JR