Although a mainstay in the dietary supplement industry, quercetin is one of those nutraceuticals that many people seem to struggle with when asked the question, “What does it do?” This article attempts to provide elucidation with a specific focus on quercetin phytosome.
Categorically, quercetin is a flavonol—one of six subclasses of flavonoid compounds1—that naturally occurs in a variety of plant-based foods and herbs, including onions, apples, berries, teas, tomatoes, broccoli, lettuce, red wine,2,3 Ginkgo biloba, St. John’s wort and American elder (Sambucus canadensis).4 Flavonoids also occur as either glycosides (with attached sugars [glycosyl groups]) or as aglycones (without attached sugars).5 In Western populations, estimated daily intake of quercetin-type flavonols is about 13.82 mg/day.6
With many potentially beneficial effects on human health, this flavonol has been the subject of various clinical studies, epidemiological studies, animal and in-vitro studies.7 Quercetin has been reported to exhibit antioxidant, antitumoral, anti-inflammatory, antimicrobial, antibacterial and antiviral properties,8,9 as well as exerting anti-aging, antithrombotic, antiaggregatory and vasodilatory effects.10,11 However, it should be noted that the low solubility and low absorption of quercetin limits its practical use,12 so research has been directed into overcoming those liabilities. More on this later in the article during the discussion of quercetin phytosome.
Clinical Research on Standard Quercetin
In using the term “standard quercetin,” I’m referring to quercetin-type flavonols (primarily as quercetin glycosides). Technically, the term quercetin should be used to describe the aglycone only; however, this is not always the case in research or in the supplement industry, where quercetin is occasionally used generically to refer to quercetin-type molecules, including its glycosides.13
In a clinical trial with 12 young men, supplementation with 1,000 mg/day of quercetin for 14 days significantly, but modestly, reduced muscle weakness associated with eccentric exercise-induced severe muscle damage when compared with placebo, and also increased performance, measured as isometric strength compared to baseline (+4.7 percent, p < 0.05).14 However, other clinical research in which the same daily dose was given did not find that quercetin improved athletic performance.15,16
In a meta-analysis17 of clinical studies, supplementation with 500-1,000 mg/day of quercetin for four to 10 weeks was shown to decrease systolic blood pressure by 3.04 mmHg and diastolic blood pressure by 2.63 mmHg compared with placebo—although just one of the studies included in this analysis was conducted on a hypertensive population.18 In other clinical research,19 patients with mild hypertension who took 1,095 mg/day of quercetin lowered their systolic and diastolic blood pressure by 7 mmHg and 3 mmHg, respectively. The research generally suggest that quercetin helps modestly lower blood pressure.
Polycystic Ovary Syndrome
In a clinical study20 of overweight women with polycystic ovary syndrome (PCOS), supplementation with 1,000 mg/day quercetin for 12 weeks reduced testosterone and luteinizing hormone (LH) levels by 9 percent and 3.4 percent, respectively, compared to baseline and placebo. Likewise, insulin resistance was improved by 17.5 percent. In other research21 on PCOS women with higher levels of insulin resistance at baseline, the same daily dose of quercetin resulted in a modest reduction in testosterone and LH levels compared with placebo.
In a preliminary prospective, double-blind, placebo-controlled trial,22 men with non-bacterial prostatitis received supplementation with 500 mg twice daily (1,000 mg/day total) of quercetin or placebo for one month. Results were that quercetin reduced pain and improved quality of life scores.
In a double-blind, randomized controlled trial,23 50 women with rheumatoid arthritis were supplemented with 500 mg/day of quercetin or placebo for eight weeks. Results were that quercetin improved morning stiffness, morning pain and after-activity pain compared with placebo.
Non-clinical (Human) Research
In in-vitro or animal research, quercetin has been shown to inhibit histamine released by mast cells basophils, suggesting an anti-allergy effect. Likewise, in animal research, quercetin has been shown to have anti-asthmatic research and counter some aspects of anaphylactic reactions.24
In-vitro research indicates that quercetin has a variety of anticancer properties, including antioxidant, antiproliferative, pro-apoptotic, cell signaling effects and growth factor suppression, as well as potential synergism with some chemotherapeutic agents. In animal research, quercetin has also been shown to inhibit cancer growth.25
Still, other research suggests that quercetin has benefits for cardiovascular disease, diabetes and diabetic complications, stomach and oral mucosa protection, immunity and infections, inflammation, injury and pain, metabolic syndrome, mood disorders and sleep.26
Clinical Research on Quercetin Phytosome
Phytosomes are a solid dispersion of natural active ingredients and a lecithin phospholipid which increases the absorption of conventional herbal extracts. There are several herbal phytosome materials with clinical research demonstrating improved bioavailability, including curcumin phytosome,27 silymarin phytosome,28 bergamot phytosome,29 green tea phytosome30 and others.
In the introduction, I mentioned that low solubility and low absorption of quercetin limits its practical use. This limitation led to the development of quercetin phytosome (Quercefit, Indena).
Quercetin Phytosome Bioavailability
Research31 was conducted to test the solubility and oral absorption of quercetin phytosome. solubility was tested in simulated gastrointestinal fluids and oral absorption in a randomized crossover pharmacokinetic study of healthy volunteers. Specifically, one dose of standard quercetin (500 mg) and two different doses of quercetin phytosome (250 and 500 mg) were administered orally in volunteers of both sexes, aged 18-50. Results demonstrated significant improvements in solubility with quercetin phytosome, as well as significant improvements in the oral absorption of quercetin phytosome. In fact, based on the very high plasma levels of quercetin, quercetin phytosome had up to 20 times greater absorption than standard quercetin (P <0.0001).
Quercetin Phytosome Study in Athletes
In this pilot registry study, the effects of supplementation with quercetin phytosome (Quercefit, Indena) were evaluated in amateur triathlon athletes. The researchers employed a specific study model of triathlon according to the ‘Sprint’ distance: 1) a swim distance in open seawater of 750 m; 2) a cycling distance of 20 km (12 miles); and 3) a 5-km run, as applied in other studies. The individual triathlon training included repetition of the defined distances eight times in 14 days in the same environment. A group of 23 athletes used quercetin phytosome (one tablet of 250 mg quercetin phytosome twice a day, with breakfast and dinner). A control group of 25 athletes did not use quercetin containing supplement, although they followed the same training and nutritional plans. At the end of the study, subjective performance, post-training pain, cramps, time to full recovery and oxidative stress were measured.
Results were that all subjects improved with training, in the total time and in all the three single events of the triathlon race, with respect to baseline. However, the improvement of time to complete the run was significantly greater in subjects on quercetin supplementation compared with the control group (-11.3 percent vs. -3.9 percent; P<0.05). Training was considered more valuable in the quercetin group compared with controls (P<0.05). Similarly, post-run muscular pain, cramps, localized pain and the post-exercise recovery time were all considered better with the supplementation according to VAS scores (P<0.05). Oxidative stress was also reduced (P<0.05).
When considering that quercetin phytosome had up to 20 times greater absorption than standard quercetin, it seems likely that it will not only work better, but that a lower dose of quercetin phytosome will be needed to elicit the same or better results. This was seen in the aforementioned athletic performance study on standard quercetin in which subjects experienced a modest improvement in performance measured as a 4.7 percent increase in strength with 1,000 mg/day, while the other studies cited found no benefit. By contrast, subjects using 500 mg/day of quercetin phytosome experienced an 11.3 percent increase in performance. So, conservatively, quercetin phytosome was more than twice as effective in improving performance, at half the dose. The data strongly suggests that quercetin phytosome is a superior form of quercetin when used in dietary supplements. VR
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Gene Bruno, MS, MHS, the provost for Huntington University of Health Sciences, is a nutritionist, herbalist, writer and educator. For more than 40 years he has educated and trained natural product retailers and health care professionals, has researched and formulated natural products for dozens of dietary supplement companies, and has written articles on nutrition, herbal medicine, nutraceuticals and integrative health issues for trade, consumer magazines and peer-reviewed publications. He can be reached at firstname.lastname@example.org.