WASHINGTONWith one third to one half of all Americans now using
some kind of dietary supplement, the need is greater than ever for
scientifically valid ways of testing and comparing the enormous range
of substances now sold with minimal FDA oversight, Vay Liang W. Go,
MD, said at the American Institute for Cancer Research conference on
nutrition. Dr. Go is associate director, Center for Human Nutrition, UCLA.
A range of compounds has been identified in recent years that appear
to have anti-inflammatory, antiangiogenic, antioxidant, and
antiproliferative properties, Dr. Go said. These include botanical
nonsteroidal anti-inflammatory drugs (NSAIDs), tannins, flavonoids,
phenyl propanoids, terpenes, and S-compounds.
But consistency is a problem. Searching a local market for competing
brands of tofu, a product now touted for the isoflavones it contains,
is revealing. You can do very well with one product on one day,
but on another day with another box, the contents are not necessarily
the same, he said. The desired constituents may vary widely
with the season, growing temperature, water, and other environmental factors.
Existing conventional chemopreven-tive agents, like NSAIDs or
estrogen, are single compounds with by-now familiar properties,
absorption rates, formulation, routes of administration, drug
interactions, safety, toxicity, and stability. Thus, it is possible
to compare one product with another with some validity, Dr. Go said.
However, such standards are not in place for evaluating dietary
supplements, he said. Many compounds contain multiple active
ingredients, and there may be many different formulations, he
said. This makes interpretation of results difficult.
Testing these compounds would require a standardized extract, based
on the kind of consistent good manufacturing practices (GMP) which
the FDA mandates for the foods and drugs under its control. Only
then, Dr. Go said, would it be possible to reliably test for
physicochemical profiles, biomarkers, solubility, stability,
absorption, excretion, and metabolism.
The Dietary Supplements Health and Education Act (DSHEA) passed by
Congress in 1994 established an Office of Dietary Supplements
Research within the National Institutes of Health, and called for
research centers to be set up around the country. Two of those
centers have been established, at the University of Illinois-Chicago
Dr. Go said that the UCLA center will identify active compounds,
assess their biological activity and availability, and conduct
Dr. Go cited several examples of forthcoming research. His lab has
developed in vitro cell lines to assay phytoestrogens found in soy
products for the chemicals that bind to two different estrogen
receptors. While some isoflavones found in soy, like genistein, have
received much attention, the percentage of genistein in any given soy
powder may vary, and genistein is not the only isoflavone present in
No one swallows pure genistein, he said. They eat
soy protein, and the observed effect could be due to some other compound.
PC-SPES, a proprietary mixture of eight Chinese herbs used for their
antiproliferative effects in prostate cancer, raises the issue of how
to test a product with multiple ingredients. Dr. Go said that markers
are needed for both the intended use of the product and possible side
effectsand for all the ingredients individually.
Green tea is another area of current interest in the marketplace, due
to the potent antioxidative properties of the catechins it contains.
However, he said, the catechin content of the teas found in stores is
not the same as that of the extracts used in the lab. We need
controlled levels of the catechins or the trials are worthless,
he said. Also, patients cannot drink green tea on their own
during a trial; it will confound the data.