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ACSM'S Health & Fitness Journal:
doi: 10.1249/FIT.0b013e31820b729d
DEPARTMENTS: You Asked For It: Question Authority

You Asked for It: Question Authority

Nieman, David C. Dr.P.H., FACSM

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David C. Nieman, Dr.P.H., FACSM, is a professor and the director of the HumanPerformance Laboratory, Appalachian State University, Boone, North Carolina, an active researcher, and an author of several textbooks on health and fitness. Send your questions to niemandc@appstate.edu.

Q:WHAT ARE FLAVONOIDS AND DO THEY REALLY PROTECT ME FROM THE STRESSES OF A HARD WORKOUT?

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A:Flavonoids provide many of the colors in fruits and vegetables, where they serve as defenders against microbes seeking a snack, radiation from the sun, and other insults. Whether flavonoids have similar functions in humans is a hot topic among scientists, but there is growing support for multiple health and fitness benefits.

Flavonoids are the major subgroup of phytochemicals or, put more simply, plant chemicals. The latest count lists more than 6,000 flavonoids, and the U.S. Department of Agriculture sorts them into six subgroups: flavonols, flavones, flavanones, flavanols, anthocyanidins, and isoflavonoids (Table 110).

Table 1
Table 1
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Most people consume between 50 and 800 mg/day of flavonoids, depending on their intake of fruits, vegetables, and tea (1,12). A medium gala apple has 24 mg of total flavonoids, a banana 15 mg, a cup of orange juice 35 mg, one-half cup of blueberries 150 mg, and cup of black tea 280 mg (10). If you like green tea, one cup provides a hefty 320 mg of flavonoids, with much of this from epigallocatechin 3-gallate or EGCG. Americans only take in about 210 mg/day flavonoids, well below the 313 mg/day in Spain (1,12). For both Americans and Europeans, the most important flavonoid sources are tea, citrus fruits and juices, beers and ales, wines, melons and berries, apples, onions, and bananas.

There is no doubt that eating a wide variety of fruits and vegetables is an important lifestyle habit that reduces the risk of cardiovascular disease and various types of cancer. The disease-protective influence of fruits and vegetables has been linked, in part, to flavonoids, but the science is still being sorted out (2,11). Most flavonoids when studied in the laboratory in purified form operate as strong anti-inflammatory and antioxidative agents. Inflammation and oxidative stress underlie most of the chronic diseases that plague modern humans, and one key countermeasure strategy is to give the body a bountiful supply of fruit and vegetable flavonoids.

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Interestingly, a big dose of just one type of flavonoid is not nearly as beneficial as a mixture of many different flavonoids (4,9). There is a growing realization that the healthful effects of single types of flavonoids are potentiated when mixed with other flavonoids, especially from separate subgroups (e.g., the flavonol quercetin with the flavanol EGCG) or included in a cocktail or extract of other polyphenols and nutrients (4). Flavonoids ingested together improve absorption and overall anti-inflammatory and antioxidative effects in the body. The plant uses a matrix of flavonoids for protection and, in a similar fashion, a flavonoid "cocktail" provides a multifaceted defensive strategy for humans. Thus, the "pharma" approach of using large doses of a single plant flavonoid is seldom successful in terms of human health.

Flavonoid-rich plant extracts are being tested by an increasing number of investigative teams as performance aids and countermeasures to exercise-induced inflammation, delayed-onset muscle soreness (DOMS), and oxidative stress (see Table 2 for a summary) (3-9). Most studies have focused on whether flavonoid-rich teas and fruit extracts can counter oxidative stress, and as summarized in Table 2, most indicate an effective response (6). Flavonoid mixtures also are good for reducing exercise-related inflammation and DOMS, with mixed results for performance outcomes.

Table 2
Table 2
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How much and for how long should flavonoid-rich extracts or supplements be used before stressful exercise bouts or intensive training periods? The dosing regimen is still under scientific scrutiny, but most studies support 1 to 3 weeks of supplementation with an extract or cocktail that provides more flavonoids than can be obtained through normal diet intake (6).

More exercise-related research has been conducted with quercetin than any other flavonoid. In one of the earliest studies with exercise-stressed cyclists, supplementation with pure quercetin (1,000 mg/day) during a 5-week period reduced illness rates but did not counter postexercise inflammation, oxidative stress, or immune dysfunction (8). In a follow-up study using a similar design, quercetin supplementation combined with green tea extract, isoquercetin, and fish oil caused a sizable reduction in exercise-induced inflammation and oxidative stress (9). Quercetin's role as a performance aid has been tested by several research teams, with mixed results (7).

I recommend a flavonoid-rich diet with a variety of fruits and vegetables for all individuals seeking health, but especially for those who favor a heavy exercise schedule. Before and during heavy training periods, the use of flavonoid-rich products, such as green tea extract, for 1 or 2 weeks should lessen inflammation and oxidative stress. An experimental mixture of quercetin, green tea extract, and fish oil knocked down postexercise inflammation by 40% to 50% and worked better than ibuprofen (7,9). More and more of these types of products will become available soon.

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References

1. Chun OK, Floegel A, Chung SJ, et al. Estimation of antioxidant intakes from diet and supplements in U.S. adults. J Nutr. 2010;140:317-24.

2. Hooper L, Kroon PA, Rimm EB, et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2008;88:38-50.

3. Hurst RD, Wells RW, Hurst SM, et al. Blueberry fruit polyphenolics suppress oxidative stress-induced skeletal muscle cell damage in vitro. Mol Nutr Food Res. 2010;54:353-63.

4. Lila MA. From beans to berries and beyond: teamwork between plant chemicals for protection of optimal human health. Ann N Y Acad Sci. 2007;1114:372-80.

5. Lyall KA, Hurst SM, Cooney J, et al. Short-term blackcurrant extract consumption modulates exercise-induced oxidative stress and lipopolysaccharide-stimulated inflammatory responses. Am J Physiol Regul Integr Comp Physiol. 2009;297:R70-81.

6. Nieman DC, Stear SJ, Castell LM, Burke LM. A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: part 15. Br J Sports Med. 2010;44(16):1202-5.

7. Nieman DC. Quercetin's bioactive effects in human athletes. Curr Topic Nutraceut Res. 2010;8:33-44.

8. Nieman DC, Henson DA, Gross SJ, et al. Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc. 2007;39:1561-9.

9. Nieman DC, Henson DA, Maxwell KR, et al. Effects of quercetin and EGCG on mitochondrial biogenesis and immunity. Med Sci Sports Exerc. 2009;41:1467-75.

10. USDA Nutrient Data Laboratory. USDA Database for the Flavonoid Content of Selected Foods. Beltsville (MD): U.S. Dept. of Agriculture; 2007. Available from: http://www.ars.usda.gov/nutrientdata. Accesssed October 6, 2010.

11. Wang L, Lee IM, Zhang SM, et al. Dietary intake of selected flavonols, flavones, and flavonoid-rich foods and risk of cancer in middle-aged and older women. Am J Clin Nutr. 2009;89:905-12.

12. Zamora-Ros R, Andres-Lacueva C, Lamuela-Raventós RM, et al. Estimation of dietary sources and flavonoid intake in a Spanish adult population (EPIC-Spain). J Am Diet Assoc. 2010;110:390-8.

© 2011 American College of Sports Medicine

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