The authors point out, however, that no one could swallow in food anywhere near the amounts of flavonoids provided in some supplements. Studies in the United States, Europe and Asia, for instance, show that people get 5-68 milligrams of quercetin in their diet per day. But a popular health food supplement recommends taking 1,000 milligrams in one swallow - 10 to 20 times more than even a high dietary intake of quercetin. There is no rhyme or reason for the dosages recommended on these bottles. The ability to take these compounds in pill form has transformed positive, protective vegetable elements into potentially dangerous compounds.
More research is needed into the adverse effects of excessive flavonoid intake.
Otherwise, they may be doing more harm than good.