Neil Osheroff and Omari J. Bandele point out that bioflavonoids are the most abundant natural source of antioxidants in the diet, and ordinarily are considered quite beneficial in protecting against heart disease, cancer, and other health problems. Despite the benefits, bioflavonoids also have toxic effects, with ingestion of high levels among pregnant women linked to rare forms of infant leukemia.

In their laboratory study, the researchers showed that bioflavonoids poison topoisomerase II in cultured human cells. This enzyme plays important roles in many critical DNA processes and removes knots and tangles from the genome. The enzyme acts by making a double-stranded cut in DNA, passing another segment of the double helix through the break, and reconnecting the broken strands. The study found that three major classes of bioflavonoids interfere with the enzyme in cells, leading to DNA damage with potential adverse health effects. The findings provide important new insights into how flavonoids act, the researchers say.-American Chemical Society