Citrus Bioflavonoids

History
Szent-Gyorgyi, the discoverer of Vitamin C, also discovered flavonoids accidentally in the late 30s. A friend given a crude vitamin C extracted from lemon found relief, but later his gums started bleeding. Szent-Gyorgyi gave a purer form of vitamin C thinking he would see better results. Instead, his friend's gums worsened! Yet upon administration of an isolated flavonoid extract, his friend's gums healed completely. Eventually, Szent-Gyorgy demonstrated that scurvy symptoms were due to a combined deficiency of Vitamin C and flavonoids.

Flavonoids were originally termed "Vitamin P" because they reduced the permeability of blood vessels. But flavonoids are so chemically diverse that they cannot be categorized as a single nutrient. The following are some herbs whose active ingredients are classified as flavonoids:

Bilberry- anthocyanins;
Strawberries- ellagic acids;
Ginkgo- ginkgoflavone glycosides;
Turmeric- curcuminoids;
Green tea- catechins;
Hawthorn berry- proanthocyanidins;
Onions- Quercetin;
Grape seeds / skin- OPCs (oligomeric proanthocyanidins).

An interesting observation was made by some Indian researchers from the prestigious All India Institute of Medical Sciences: the vitamin C in the extract of the fruit amla, which has the highest concentration of ascorbate in any plant, had over ten times the bioavailabilty of synthetic Vitamin C. Careful analysis revealed that the tannins present in the amla fruit protected and enhanced the vitamin C activity. Other studies have found that the cancer cell growth inhibitory actions of the flavonoid quercetin were considerably enhanced by vitamin C. The effect on the vitamin may be due to its ability to recycle oxidized vitamin C: when antioxidants neutralize free radicals, they become themselves weak prooxidants. Flavonoids display an "antioxidant boosting" effect, returning ascorbate to its active antioxidant form. 

References

i. Ginter. E. (1995) "The role of antioxidants in the prevention of tumors". Bratisl. Leh Lish, 96: 195-209

ii. Miller, A. (1996). "Antioxidant flavonoids: Structure Function and Clinical Usage". Alt. Med. Rev. 1:103-111.

Antioxidant diet supplementation enhances aerobic performance in amateur sportsmen.
J Sports Sci. 2007 Sep;25(11):1203-10.
Aguiló A, Tauler P, Sureda A, Cases N, Tur J, Pons A.

The effects of antioxidant diet supplements on blood lactate concentration and on the aerobic and anaerobic thresholds and their adaptations to training were analysed. Fifteen amateur male athletes were randomly assigned to either a placebo group or an antioxidant-supplemented group (90 days supplementation with 500 mg x day(-1) of vitamin E and 30 mg x day(-1) of beta-carotene, and the last 15 days also with 1 g x day(-1) of vitamin C). Before and after the antioxidant supplements, the sportsmen performed a maximal exercise test on a cycle ergometer and maximal and submaximal physiological parameters were assessed together with blood lactate concentration. Maximal oxygen uptake (VO(2max)), maximal blood lactate concentration, and the maximal workload attained rose significantly in both groups after the 3 months of training. At the end of the study, maximal blood lactate concentration was lower in the group that took supplements than in the placebo group. The percentage of VO(2max) attained at the anaerobic threshold rose significantly in both groups after 3 months of training, although the final value in the supplemented group was higher than that in the placebo group. Antioxidant diet supplements induced lower increases in blood lactate concentration after a maximal exercise test and could improve the efficiency in which aerobic energy is obtained.


Flavonoids and risk of squamous cell esophageal cancer.
Int J Cancer. 2007 Apr 1;120(7):1560-4.
Rossi M, Garavello W, Talamini R, La Vecchia C, Franceschi S, Lagiou P, Zambon P, Dal Maso L, Bosetti C, Negri E.

The relation between 5 classes of flavonoids (flavanones, flavan-3-ols, flavonols, flavones and anthocyanidines) and esophageal cancer was investigated using data from a case-control study conducted between 1992 and 1997 in 3 areas of northern Italy. The study included 304 cases (275 men, 29 women) with a first diagnosis of squamous-cell carcinoma of the esophagus and 743 controls (593 men, 150 women) with no history of cancer, admitted for acute illnesses, unrelated to tobacco and alcohol consumption, to major hospitals of the areas under surveillance. Dietary habits were investigated using a validated food frequency questionnaire. Odds ratios (ORs) and 95% confidence intervals (CI) were computed after allowance for age, sex, study centre, years of education, alcohol drinking, tobacco smoking, body mass index and energy intake. An inverse association emerged between flavanone intake and esophageal cancer risk (OR=0.38 for the highest vs. the lowest quintile, 95% CI=0.23-0.66). The inverse relation between flavanones and esophageal cancer tended to be stronger in those who drank >or=6 drinks/day. In conclusion, this study suggests that flavanone intake is inversely associated with esophageal cancer risk and may account, with vitamin C, for the protective effect of fruit, especially citrus fruit, on esophageal cancer. (c) 2006 Wiley-Liss, Inc.