Flavonoids in supplements

Enhancement of vitamin C action

Flavonoids, particularly citrus bioflavonoids, are often given with vitamin C; for example in the treatment of colds, bleeding problems, bruising and ulcers. Flavonoids may also have antiviral activity.

Flavonoids in supplementsFlavonoids in cardiovascular disease

As flavonoids have been shown to have antioxidant properties, they are able to protect against heart disease, which may explain the so-called 'French paradox.' This refers to the fact that the French eat much larger amounts of saturated fat and have higher cholesterol levels and blood pressures than Americans, yet are 2.5 times less likely to die of coronary heart disease.

Red wine is a good source of flavonoids and many people have suggested that the liberal French consumption of red wine protects against coronary heart disease. Several studies have found that a glass or two of wine daily protects against heart disease and it seems likely that red wine is more protective than white wine, suggesting that the benefits might be unrelated to the alcohol.

Researchers involved in the Zutphen elderly study assessed the flavonoid intakes of 805 men aged from 65 to 84 years in 1985. The major sources of flavonoid intake were found to be tea, onions, and apples. The men were then followed up for five years, during which time 43 men died of coronary heart disease. Fatal or nonfatal heart attacks occurred in 38 of 693 men with no history of heart attack at the beginning of the study. The results showed that those with the highest flavonoid intake had less than half the risk of death from heart attack when compared to those in the lowest intake group.

In a 1996 study, Harvard researchers assessed the links between heart disease and flavonoid intake in 34 789 male health professionals aged from 40 to 75. Among the 4814 men who reported that they had previously had coronary heart disease, flavonoids showed a protective effect against death from heart attack.

High flavonoid intakes also seem to protect against stroke. Researchers involved in a 1996 Dutch study assessed the diets of 552 men aged 50 to 69 years in 1970 and followed them up for 15 years. The results showed that those with the highest intakes of dietary flavonoids (mainly quercetin) had around 75 per cent less risk of stroke compared to those with the lowest intakes. Black tea contributed about 70 per cent of the flavonoid intake in the study. Men who drunk more than four cups of tea had around a third of the risk of stroke when compared to those who drunk less than two cups of tea. However, in a 1997 study done in Wales, researchers did not find a reduced risk of heart disease with increasing tea consumption. Black tea seems to be more effective in raising antioxidant levels than tea with milk.

Flavonoids in supplementsFlavonoids are useful in the treatment of high blood pressure due to their capillary-strengthening and blood vessel-dilating effects. They are also useful in capillary fragility disorders such as easy bruising, bleeding of the gums, and also in circulatory disorders of the retina of the eye. They are particularly useful in the treatment of vein and capillary problems such as varicose veins, venous insufficiency (poor return of blood to the heart from the veins of the legs), and eye problems such as diabetic retinopathy and macular degeneration.

Flavonoids in green tea

Green tea contains several polyphenols, the most active of which appears to be epigallocatechin gallate. These compounds have several beneficial effects, including protection from heart disease.

Green tea has been shown to lower cholesterol. In a 1995 Japanese study researchers investigated green tea consumption of 1371 men aged over 40 years. Analysis of their blood samples showed that increased consumption of green tea was linked to decreased serum concentrations of total cholesterol and triglyceride, and increased levels of beneficial HDL cholesterol together with decreased levels of LDL and VLDL cholesterols. Those who drank ten or more cups per day showed better liver function measurements.

Research from Japan has linked green tea consumption with a reduced risk of stroke. In a four-year study of almost 6000 women, the incidence of stroke and cerebral hemorrhage was at least twice as high in those who drank less green tea (fewer than five cups a day) than in those who drank more (greater than or equal to five cups daily).

Flavonoids in cancer

Flavonoids may also help to protect against cancer. Many laboratory experiments have shown that various flavonoids can inhibit the growth and proliferation of cancer cells. Recent animal experiments looking at tumor onset in mice found beneficial effects when their diets were supplemented with red wine solids (which contain no water or alcohol).

Flavonoids in supplementsIn a study published in 1997, Finnish researchers investigated the links between the intake of flavonoids and subsequent risk of cancer in 9959 Finnish men and women aged from 15 to 99 years and initially cancer-free. During thefollow-up period, 997 cancer cases and 151 lung cancer cases were diagnosed. The results showed that a high intake of flavonoids reduced the risk of all types of cancer. An inverse association was observed between the intake of flavonoids and incidence of all sites of cancer combined. Those with the highest flavonoid intakes had almost half the risk of cancer compared to those in the lowest intake groups.

Researchers involved in the Iowa Women's Health Study analyzed the tea drinking habits of over 35,000 postmenopausal women and found that those who drank more than two cups of tea a day were 32 per cent less likely to have cancers of the mouth, esophagus, stomach, colon and rectum. They were also 60 per cent less likely to have urinary tract cancer. In those who drank four or more cups per day, the risk of cancer was lowered by 63 per cent.

Onions are high in flavonoids, which may explain the links between their consumption and reduced cancer risk. Researchers involved in The Netherlands Cohort Study assessed the links between onion consumption and the risk of stomach cancer in 120,852 men and women ranging in age from 55 to 69 years. Those whose onion intakes were high had around half the risk of stomach cancer when compared to those whose intakes were low.

Green tea

Green tea preparations and extracts have been shown to inhibit tumor formation and growth in laboratory experiments. The evidence for the protective effect of green tea is strongest for cancers of the digestive tract.

Most of the research on the health benefits of green tea has been carried out in Japan and China. In a study published in 1997, Japanese researchers investigated the links between green tea and cancer in 8552 people over 40. During a follow-up period of nine years, there were 384 cases of cancer. The results showed a lower risk in those who drank green tea, especially among women drinking more than ten cups a day.

The results of a Chinese study suggest that drinking green tea can reduce the risk of esophageal cancer. The study involved 902 patients, aged 30 to 74, who were diagnosed with cancer of the esophagus from October 1990 through January 1993. A group of 1552 healthy volunteers were used as controls. Histories of cancer in the family, diet, smoking and drinking habits were taken into account. The researchers found that for those who refrained from smoking or drinking alcohol, green tea consumption reduced the risk of esophageal cancer in men by 57 percent, and 60 per cent in women. For those who smoked or drank alcohol, green tea exerted little protection.

Another Chinese study showed that drinking green tea also reduced the risk of stomach cancer. This study involved 711 patients and 711 controls. The results showed that those who drank green tea had 30 per cent less risk of stomach cancer." Other studies have shown reduced risks for colon cancer. Green tea may also protect against the carcinogenic changes caused by cigarette smoke.

In a study published in 1998, Japanese researchers investigated the effects of drinking green tea on the progression of breast cancer. The study involved 472 patients with stage I, II, and III breast cancer. The results showed that increased consumption of green tea was linked to a decrease in the spread of breast cancer in premenopausal women. In a follow-up study, the researchers found that increased consumption of green tea was correlated with decreased recurrence of stage I and II breast cancer.

Flavonoids in allergies and autoimmune disease

In addition to their antioxidant effects, the ability of flavonoids to affect enzymes involved in the production of inflammatory substances means they may be useful in the treatment of asthma, allergies, bursitis, arthritis and inflammatory bowel disease.


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