I think I have not wasted my time , because now I understand that is a very complex analysis , thanks for the explanation. I will follow your advice

Even though there isn't any real consensus on this topic across the board, when you are looking at them on an individual basis, you can use the literally hundreds of studies that are out there as a 'guideline' to help you determine what would be beneficial on an 'as needed' basis. Please keep in mind that some of them require very specific delivery systems (e.g. oil) to maximize uptake. The term Flavonoids covers a lot or territory, so you may need to be a bit more specific.

The human body don't like these flavonoids. He throws them out as fast as possible and principally its a poison! The nutrition supplement industry tried to establish such products on the market. In Germany most of this products were prohibited. Flavonoids can do both - be antioxidant but also can damage the DNA. The oxidant/antioxidant status in the human body is a much more complex thing than thought before. The easy answer for your question is - you should intake so much flavonoids as you naturally eat with your food.

I have not seen any research that addresses Alexander's thought on Flavonoids. There are literally hundreds of studies that show certain types have a positive effect on various systems in the body. This is not my opinion, it is drawn from peer reviewed studies. Yes, too much of anything is not a good thing, but I would not call them a poison. There really isn't enough room here to get into a long discussion regarding this material. But I will give you an example, grape seed extract 95% has been shown to have a direct impact on CV health. I have personally seen it reverse the appearance of spider veins in those who have been treated with radiation. I don't believe your original question discussed why you wanted to use this material. But one of the answers is about their use as an antioxidant. I don't like this term, I would prefer to use the term free radical scavenger. Using supplements appropriately and eating foods that reduce free radical damage is an appropriate use. Certain pathologies require an increase in dose rate for food and or supplements for them to be therapeutic. And since most food (unless it is organic) are not grown in soils that are nutrient dense, and are depleted of almost any nutrient value, food may not always be your best and highest source of beneficial nutrients and phytochemicals. So, as I suggested before, it would be good to review what is currently published, and then draw your conclusion from that.

A healthy balanced meal is the best solution without worrying about details of individual content composition.

There are literally thousands of different flavonoids, from isoflavones like genistein in soy to flavonols like myricetin in currants, flavonols like quercetin in apples, flavones like naringenin in oranges, and chalcones like xanthohumol in hops. Few, if any, have the same set of biological activities. Some are cytotoxic, others are not. Some have estrogen-like activity, others don't. Some induce phase II enzymes, others don't. This means that there cannot be an optimal flavonoid consumption level without defining exactly which specific compounds we are referring to. The best way to go about this is to eat lots of fruits and vegetables (5-9 servings a day depending on size and gender), get a variety of types, and hope for the best. Meanwhile, there is a good body of research about the specific effects of particular flavonoids, but not enough on any of them to call for a minimal intake level. We do want to learn more about what is in our foods and must not assume that it is all good and healthy because it is natural and plant based. Taking flavonoids as concentrates, extracts or in purified form seems not a good idea at this time because many are much more potent than one might think and many have unexpected and sometimes harmful effects.

Thanks for your answer, It has extended my vision. However, It would be possible to take servings to obtain an equivalent amount of flavonoids according to each group of flavonoid present in certain species of plants?

Thanks to everybody.

The problem is just that there is no such thing as equivalent amounts of flavonoids by group. Even with a particular group, say isoflavones, the various compounds can differ substantially. What's worse, they may be similar in respect to one property, such as redox potential, but differ in terms of estrogen-like activity or solubility in blood, or bioavailability etc. EGCG, for instance, is a specific inhibitor of dihydrofolate reductase. That does not necessarily mean that EG or EGC inhibit the enzyme to the same extent. They may not inhibit it at all. So we should really avoid assuming equivalent potency just based on some structural grouping.

For the required dietary intake of flavonoids, you only need to take enough of green vegetables and fruits (regularly with a balanced diet) which are normally rich source of polyphenolic compounds which include the so call flavonoids.

Dear Emily, It is a very complex question and even you find its answer it will not has a practical aspect for daily nutritional program. Antioxidant content of food, fruits,...are not fix amount and vary vastly depend on row materials, preparation, transportation, storage, cooking,..... On the other hand our daily requirement is vary vastly too, depends on our age, genetic, stress, pollution, activity, bio-availability of a fix amount of antioxidant in various people. It means may be one day your minimum amount is zero without any problem and one day you need twice amount of average daily intake. I think in this situation determination of overdose and its side effect is more easily.

The function of flavonoids in vivo and in vitro are complex and not well understood. The therapeutic value of certain flavonoids can only be evaluated by well performed controlled clinical tials. We need interventional studies with valid clinical endpoints which are expensive to do. There is the possibillity that flavonoid deficiency syndroms exsist. but to prove this we need more than epidemiological studies.