- Fruits and vegetables keep you healthy, but some of their
chemical components, concentrated and sold in high doses as
flavonoid supplements in health food stores, are likely to
make you sick, warn scientists at the University of California,
Berkeley's School of Public Health.
applies to such popular products as ginkgo pills, quercetin
tablets, grape seed extract and flaxseed, which contain high
concentrations of flavonoids.
vitamins C and E, flavonoids become dangerous at the high
doses available in some supplements, which are not regulated
by any governmental agency, according to Martyn Smith, UC
Berkeley professor of toxicology.
they may protect against some forms of cancer when consumed
in the diet, plant flavonoids actually have the capacity to
become carcinogenic at higher levels, said Smith. High doses
of these chemicals also carry other health risks including
a small but documented risk for a rare form of leukemia in
some Americans could be poisoning themselves with these supplements."
said Smith. "The potency of concentrated plant flavonoids
in some of these products has been radically underestimated."
do eat fruits and vegetables," he said. "But stop taking these
UC Berkeley graduate student Christine F. Skibola are publishing
their findings on the health effects of high flavonoid intake
this week in the English scientific journal, "Free Radical
Biology and Medicine."
describes the many biological activities of flavonoids, showing
that high levels of plant flavonoids can bind with and damage
chromosomes and DNA in cell cultures. The effects follow a
gradient, with protective effects at low levels and mutagenic
effects at high levels.
also alter the activity of various enzymes and interfere with
hormone metabolism, particularly estrogen and thyroid hormones,
according to Smith and Skibola.
these adverse effects is likely to occur at dietary levels
of consumption. In fact, Asians and vegetarians are known
to have less cancer than other people, in part because of
their high consumption of flavonoids in soy, green tea and
point out, however, that no one could swallow in food anywhere
near the amounts of flavonoids provided in some supplements.
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.
when we get worried," said Skibola. "There is no rhyme or
reason for the dosages recommended on these bottles. These
compounds need to be regulated."
that natural is safe is completely wrong," Smith added. "The
ability to take these compounds in pill form has transformed
positive, protective vegetable elements into potentially dangerous
is needed into the adverse effects of excessive flavonoid
intake. But Smith and Skibola say that for now, "the public
should be wary of the beneficial claims made for these supplements
and limit their intake until their safety is established.
Otherwise, they may be doing more harm than good."