Flavonoids have received a lot of attention because of their impressive antioxidant properties. These compounds appear to be even more effective than the more familiar antioxidants like vitamins C and E in their effects of protecting low-density lipoproteins (LDLs) from oxidation. It appears that if we are eating lots of fruits, vegetables, grains and legumes, the consumption of flavonoids would far exceed the consumption of other antioxidants, such as vitamin C. In fact, flavonoid consumption is estimated to be between 200 and 1,000 milligrams a day.
Hundreds of studies on flavonoids have demonstrated that they may also lower cholesterol levels, offering further protection against cardiovascular disease. They also possess antiviral, anticarcinogenic, anti-inflammatory and antihistamine activities and may therefore be useful in preventing and/or treating a wide variety of conditions. Many studies have demonstrated the effectiveness of flavonoids in the prevention and treatment of various cancers. These studies, which have included treatment of cancers resistant to chemotherapy, have involved both cell lines, animal and human studies.
In a 2002 study of 10,000 Finnish men and women, researchers discovered many specific associations between certain flavonoids in the diet and several chronic diseases. They found that people with higher quercetin intakes had lower mortality from ischemic heart disease; persons with high hesperetin, kaempferol and naringenin intakes had a lower incidence of cerebrovascular disease; men with higher quercetin intakes had a lower lung cancer incidence; men with higher myricetin intakes had a lower prostate cancer risk; people with higher quercetin, naringenin, and hesperetin intakes had a lower asthma incidence; and higher quercetin and myricetin intakes were associated with a trend toward a reduction in risk of type 2 diabetes.
Some flavonoids are classified as phytoestrogens and encourage a better balance of good to bad estrogen by binding to sites for bad estrogen. An excess of the bad estrogen (estradiol) is implicated in breast cancer, prostate cancer, menopausal symptoms, premenstrual symptoms, endometriosis, fibrocystic breast disease, and possibly other hormonally related disorders. Flavonoids help the body metabolize estradiol into estriol, the safe and protective form of estrogen. In fact, estriol is the preferred form of estrogen used in Europe in hormone-replacement therapy.
Quercetin may be active against many types of cancer, including breast, prostate, colon, gastric, head and neck, leukemia, lung melanoma, liver, ovarian, cervical and rhabdomyosarcoma. Although it's synergistic with various chemotherapy drugs as well as radiation, unlike these conventional forms of cancer treatment, when quercetin is used alone, it damages cancer cells only. Quercetin can stop the growth of blood vessels that feed the cancer, inhibit the production of tumor-stimulating hormones and hormone-like substances, stimulate the immune system, and scavenging mutation-causing free radicals. Most of the research on proanthocyanidins has used Pycnogenol from the bark of the French Maritime Pine tree rather than grape seed extract, which also contains this type of flavonoid. There has also been a lot of studies on Activin, in particular on cancer and cardiovascular effects. Much of this research has focused on the ability of these substances to act as antioxidants, and on their beneficial effects on many types of circulation problems. Human trials have shown that these flavonoids can prevent peripheral hemorrhage, swelling of the legs due to water retention, diabetic retinopathy, and high blood pressure. Researchers have also reported success in using these substances to treat varicose veins, leg cramps, and other problems arising from insufficient blood flow. When buying this flavonoid, look for these forms and other supplements standardized to at least 20% proanthocyanidins.
Flavonoids are found in fruits, vegetables, nuts, seeds, grains, and legumes (particularly soybeans and soy products), and in beverages such as tea, coffee, and wine. Quercetin is the major flavonoid in our diet; it"s estimated we eat approximately 25 mg per day from onions, apples, and other commonly eaten foods.
Those that are easiest to find include bioflavonoid complex, curcumin, hesperidin, Pycnogenol, quercetin and rutin. Note that all flavonoids should be taken with vitamin C, as they increase vitamin C absorption and are themselves powerful antioxidants. For optimum general health, the basic optimum daily Intake for flavonoids--alone or in combination--is: 250-1,000 mg for men and women (to be taken with an equivalent amount of vitamin C) 50-300 mg for Pycnogenol, Activin and other sources of proanthocyanidins (e.g. grape seed).
Shari Lieberman, PhD, CNS, FACN earned her Ph.D. in Clinical Nutrition and Exercise Physiology from The Union Institute, Cincinnati, OH. Dr. Lieberman's newest book, "The Real Vitamin & Mineral Book" (Avery Publishing Group; 2003) is available in bookstores. For more info, visit: www.drshari.net