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Give Your Immune System a Boost with Quercetin

By Monique Ryan | July 27, 2010, 12 a.m. (ET)

Hopefully you have remained healthy through all your hard training this season, avoiding an annoying summer cold or other upper respiratory tract infection.  Unlike moderate physical activity, which provides an immune boost, the volume and intensity demands of serious training result in numerous changes in your immune system that require you to remain on high alert for preventing infection. Appropriate nutritional supplementation can be one immune boosting strategy and one such promising product appears to be quercetin.

Quercetin is a powerful antioxidant, anti-histamine and anti-inflammatory, and is the most prominent of over 5,000 flavonoid compounds found in food.  Some of the best sources of quercetin include apples, onions, blueberries, kale, tea, and broccoli.  Our flavonol intake can range from 13 to 64 mg daily and we can absorb significant amounts of quercetin from food or supplements. Long-term, high dosing of quercetin appears to be safe.  Studies have measured that a higher quercetin intake from food compared to a lower quercetin intake is associated with reduced risk of ischemic heart disease, type 2 diabetes, asthma, and various types of cancer.

So just how does this powerful antioxidant quercetin, which is five times from potent than vitamin C, possibly benefit the hard training triathlete?  Several studies have been conducted with athletes. One such study, conducted by Dr. David Nieman of Appalachian State University, had 40 cyclists take 1000 mg of quercetin or a placebo daily for 3 weeks, before, during, and for 2 weeks after a 3 day period of hard training. During this hard training trial, subjects cycled for 3 hours at 57% watts max.  While parameters that measure immune dysfunction, inflammation, and oxidative stress were not improved with the quercetin supplementation, the supplemented group had a lower incidence of upper respiratory tract infection in the two weeks following the hard cycling.

With these promising results, Nieman followed with another study using the same exercise protocol in which 1,000 mg of quercetin was combined with 30 mg of ECGC (an antioxidant polyphenol found in green and white teas) and 400 mg of omega-3 fatty acids. “We know that quercetin supplementation increases plasma quercetin, but it may need help from other supplements, so we added the ECGC and omega-3s,” said Nieman. Omega-3s are known to have an anti-inflammatory effect and ECGC keeps plasma quercetin levels elevated longer. Nieman speculated that the additional ingredients would result in some immune parameter changes, and was not disappointed. “Our results were rather dramatic,” states Nieman.  “The quercetin-EGCG-EPA/DHA supplement significantly countered exercise induced increases in oxidative stress and inflammation. The incidence of URTI was down by about one-third during the two-week follow-up period but the number of subjects, unlike the initial study, was too low for enough statistical power to show group differences.”

Another study looked at performance effects of quercetin. Conducted at Pepperdine University compared two mixes of antioxidants and vitamins to one another- one antioxidant mix contained 300 mg of quercetin and one did not. They both contained vitamin C, green tea extract, vitamin E, and various B vitamins.  Cyclists took 300 ml of each supplement twice daily for 6 weeks.  They completed a 30 mile time trial before starting each supplement and at 3 weeks and 6 weeks of supplementation. Time to complete the 30 km time trial as well as time to complete the final 5 km of the course was significantly improved with the antioxidant mix that contained quercetin. There was no significant improvement in the time trial performance in the antioxidant mix that did not contain quercetin. More performance studies are needed as well as further study of the mechanism behind the results.

“There are two huge benefits to the supplement mix of quercetin, omega-3’s and ECGC. First, you dampen the oxidative stress and inflammation following exercise,” said Dr. Nieman. “It is like putting a cold pack on a sore muscle.” But Nieman feels that the anti-infection effects are the most dramatic. “Athletes are always concerned about getting sick before a race.”

Nieman has also studied the effects of quercetin on mental performance including the ability to concentrate and act in a vigilant manner after intense physical activity. In the same exercise and supplementation protocol described above in Nieman’s studies, subjects were tested prior to and during the three day period of intense cycling. All the cyclists experienced a slowing of reaction time across the three days. However the effect differed for the quercetin supplemented group, indicating that the supplement may protect against post-exercise mental fatigue. This effect was more pronounced after three days of intense exercise compared to after the first day.

Quercetin is found in antioxidant mixes in liquid form and also in chewable form.  You can also purchase quercetin in capsule form. The “aglycon” form is well absorbed and this supplement is most effective when consumed with other antioxidants.

While the early results of quercetin are very promising, in the interest of staying healthy, it is also important to know about other strategies that can keep your immune system strong, or not.

  • Carbohydrate beverage consumption of 60 g of carbohydrate per hour (or more if your energy needs are higher) during intense endurance training sessions can lower levels of stress hormones such as cortisol and epinephrine, and inflammatory immune responses.
  • Studies that have looked at vitamin C and vitamin E supplementation have not been found them to counter the effects of exercise induced immune dysfunction. In fact one study conducted at Kona found that supplementing with 800 IU a day for two months increased oxidative stress and blood levels of cytokines.
  • Reduced blood glutamine levels have been found in response to intense endurance exercise. However, the majority of studies have not demonstrated that glutamine ingestion can reduce exercise-induced immune dysfunction, even though it kept blood glutamine levels from being depleted.
  • Other supplements are also undergoing study. Animal data for beta-glucan, a polysacchriade found in the bran of oat and barley grains, and for the spice curcumin point to the need for testing in athletes. Additional research will provide an answer.

Ultimately, the goal is to provide endurance athletes with recommendations for a cocktail of supplements that will lower their risk of infection, reduce oxidative stress, and have a positive effect on their immune systems.

Monique Ryan, MS, RD is the author of Sports Nutrition for Endurance Athletes, 2nd edition (VeloPress 2007). Click here to view more about the book or purchase. She was a member of the Athens 2004 Performance Enhancement Teams for USA Triathlon and USA Cycling Women’s Road Team. She is owner of Personal Nutrition Designs and offers her sports nutrition “E Program” at