Down the Rabbit Hole with Quercetin- Tigger scientist illustration

Down the Rabbit Hole with Quercetin

What are quercetin supplements, and how can they help your horse? We go down the rabbit hole to learn more about this powerful flavonoid, how it supports body systems, and how to ensure it’s effective for your horse.

One evening I decided to stroll down the internet aisles looking at quercetin supplements for horses. What I found surprised me: not only were the forms of quercetin not advanced in terms of bioavailability, but the dosage was only suitable for humans, not horses.

This is a common problem among supplement products for humans and animals. One or several recognizable or popular ingredients are added to a formula to increase customer interest. But the amounts on the label often are not enough to provide efficacy.  

Quercetin is a potent flavonoid found in various foods. Flavonoids were discovered in 1936 when American biochemist Albert Szent-Gyorgyi was researching ways to treat scurvy. He won the 1937 Nobel Prize in Physiology for his discoveries of ascorbic acid and the biological activity of flavonoids which were then referred to as Vitamin P.

I first became acquainted with quercetin in the late 1980s when several human supplement companies began using it as an ingredient. At that point, not as much was known about its powerful properties. It has since become a research hotspot, particularly for its antioxidant activity.

What Does Quercetin Do?

Quercetin is a versatile antioxidant, providing protective abilities, anti-inflammatory support, gastro protective support, and inhibition of histamine.1

My interest in using Quercetin came about when I read the thesis paper “Effects of Quercetin on Exercise Potential and Exercise-Induced Cytokines in the Horse.1b” The conclusion of this study noted:

“When dosed with quercetin, the horses were able to run significantly longer and took significantly less time to recover following exercise.”

The thesis also stated, “Assuming that quercetin’s method of action is to disrupt transcription of inflammation-inducing cytokine genes via that NP-kB pathway, it would avoid most, if not all, of the negative side effects associated with NSAID use.

Quercetin benefits horses by:

  • Acting as an immune modulator; it is very helpful for horses with allergies, Lyme Disease, and EPM.3
  • Reducing the histamine response, which is very important for horses with allergies.4
  • Reducing lung inflammation, which can benefit horses with asthma. It can be beneficial for horses that need respiratory support during hot weather and in periods of intense training or competition.5
  • Providing gastrointestinal protection against oxidative stress and inflammation. Studies have shown that quercetin can help with Inflammatory Bowel Disease.6
  • Supporting gut microbiota diversity and acting as a prebiotic for gut dysbiosis.7
  • Reducing Reactive Oxygen Species (ROS) caused by environmental and toxicological factors. It can support the strengthening of the antioxidant defense systems in the body. Reduction of oxidative stress levels can help optimize sports performance and recovery.8

Quercetin Supplements for Horses | BioStarUS

Quercetin in food

Quercetin is found in various foods such as apples, onions, dark cherries, grapes, raspberries, citrus fruits, brassica vegetables, tea, and tomatoes, as well as the medicinal botanicals Ginkgo Biloba, Japanese Pagoda Tree, and Sambucus.

Bioavailability and Dosage for Quercetin

There are two key factors with quercetin: Bioavailability and Dosage

Bioavailability isn’t just a concept, it’s an actual measurement of the amount of absorption that reaches systemic circulation. As a formulator, it is one of my most important evaluations of a raw material. There can be no efficacy without bioavailability.

As I dug through research on quercetin’s effects, a consistent issue of bioavailability was noted in the studies. I went through current equine supplements on the market that contain quercetin and wondered, how can we be sure the quercetin is effective?

Absorption and bioavailability of Quercetin

The most common forms of quercetin in supplements are quercetin glycoside, quercetin aglycone, and quercetin dihydrate.  Numerous studies have shown that these forms of quercetin have poor solubility that limits bioaccessibility and bioavailability. One human study indicated that quercetin glycoside absorption was only 3%-17% at a dose of 100 milligrams. Numerous published research on quercetin continues to point out the challenges with quercetin absorption.

Research has shown very poor oral availability of quercetin glucoside, the form of quercetin found in most supplements.9 Quercetin glucoside has poor water solubility, and low oral absorption in supplement form. Some estimations are that only 20% of quercetin supplementation reaches the blood.

Other factors that affect bioavailability are the composition of the gut microbiota, pharmaceutical medications, and metabolic disease.10

Quercetin is a lipophilic compound, therefore dietary fat enhances its bioavailability.

Quercetin consumed in whole food form (eating an apple, for instance) has higher bioavailability than supplemental quercetin glucoside. One apple supplies 13 mg of quercetin. To reach a minimum therapeutic level in horses requires 500 mgs per 1,000 pound horse.11 That’s a lot of apples!

Quercetin Dosage for Horses

Assessing the correct dosage of various herbs or nutraceuticals for horses often relies on a multiplication factor of 3-5 times the human dose, sometimes more. 

In the case of Quercetin, the common dose for humans ranges from 100 milligrams to 200 milligrams per day.  So if we use 200 milligrams and multiply that by 3 we get 600 milligrams as a starting point for dosing in horses.  If we go higher and multiply by 5, we get 1,000 milligrams as a dose.

For example, the human recommended dietary allowance (RDA) of vitamin E, is 22.5 IU per day.  But therapeutic levels are generally anywhere from between 200-1,000 or more IUs per day.

The recommended minimum daily intake for horses, based on the National Research Council (NRC) is 1-2 IU per kg of body weight, which would be 500 IU per day for a 1,000 pound horse. Therapeutic levels are considerably higher: anywhere from 2,000 to 5,000 or more IU’s per day.

If we take the high end of the human therapeutic dose, 1,000 IUs, and multiply it by 5, we get the higher end of the therapeutic dose for horses: 5000 IUs per day.

The equine supplements I looked at containing quercetin provided dosages ranged from 105 to 295 milligrams per day. One did contain 400 milligrams of quercetin, which I was happy to see.  But still based on 200 milligrams of quercetin for humans, 400 milligrams for horses is probably not enough therapeutically. It would need to be 600 milligrams.

It’s possible that some companies use the lower end of the human dose: 100 milligrams and multiply that by a factor of 3, getting to 300 milligrams or more. However, from my perspective of pouring over research and published studies on the low bioavailability of quercetin, using the low human dose would need a multiplier of 7.

Finding Quercetin Phytosome®

A study published in 2018 demonstrated the bioavailability of a novel form of quercetin called Quercetin Phytosome®. Developed by a company in Italy, this unique form of quercetin that’s bound to lecithin showed “significant improvements in both vitro solubility and oral absorption (in terms of both exposure and maximum concentration achieved) by healthy volunteers in a human clinical study as compared to unformulated quercetin.9

The study showed that Quercetin Phytosome® facilitated very high plasma levels of quercetin; up to twenty times more than usually obtained from quercetin glucoside, demonstrating that it’s the most bioavailable form of quercetin on the market.

What makes quercetin phytosome different is the fact that it’s bound to lecithin. Phospholipids have shown to improve solubility, oral absorption and biological effects in other antioxidants such as Astaxanthin. Not really a surprise that quercetin, too, benefits from phospholipids such as lecithin.12,13

Where does the quercetin in Quercetin Phytosome® come from?

Quercetin Supplements for Horses | BioStarUSQuercetin Phytosome® derives quercetin from the flower buds of Sophora japonica L (Huaihua in Traditional Chinese Medicine) also known as the Japanese pagoda tree. It has thousands of years of use in humans and animals.

Biostar’s Quercetin Phytosome®:

Biostar only uses quercetin phytosome®. We use this form of quercetin because of its proven absorption.  What is the point of quercetin supplementation if it cannot reach the small intestine?

In our upcoming allergy/respiration supplement Aller-X EQ we start with the human dose of 200 milligrams and multiply by five to provide 1,000 milligrams of quercetin per serving for horses.  Our beta tests on various horses showed us that this dose provides efficacy.

Quercetin Phytosome® in the US

Currently there are several American human supplement companies that use this form of quercetin in their supplements. I have been unable to find any horse or dog supplements that provide Quercetin Phytosome®.

I think I know why. The cost of this patented raw material is significant. It is so expensive that I nearly had a heart attack during consultations with its Italian producer.

In the end, we couldn’t settle for second best, so we decided on the highly-bioavailable Quercetin Phytosome®. The health benefits of quercetin for horses and dogs is too great to use a cheaper and less bioavailable version.

Quercetin Phytosome® at BioStar

BioStar will be introducing Quercetin Phytosome® in several new Biostar products in 2021.

Optimum Defense 60 serving bagThe first is Optimum Defense, now available. This is an addition to our Optimum line, with immune support from a wide range of researched immune support ingredients including bovine colostrum, turkey tail mushrooms, cordyceps mushrooms, Astragalus, and Quercetin Phytosome®.

We’re also working on a combination allergy/ respiratory formula for horses, as well as a canine immune support formula. Both of these formulas will contain Quercetin Phytosome®.

It’s very exciting to bring another patented extract to the equine industry. Quercetin Phytosome® joins the other patented extracts that we have introduced to horses through our products: Capros® Amla, Primavie® Shilajit, Crominex® Trivalent chromium with Amla and Shilajit, and KSM-66 Ashwagandha.

We’ll continue searching high and low to bring novel, highly-bioavailable ingredients like Quercetin Phytosome® to your horses and dogs.

Look for Aller-X EQ to be released in JUNE 2021!


This post has been updated from the original January 2021 post.


Tigger Montague | BioStar USAbout the Author: With over 30 years experience in the equine and human supplement industry, Tigger Montague knows nutrition from the synthetic side as well as the whole food side. She started BioStar US in 2006 with formulas she created in her kitchen. Before she started the company, she was an avid rider and competitor with eventing and show jumping, until she got hooked on dressage in the late 1980’s. She has competed on horses she’s owned and trained all the way from training level to Grand Prix.



  2. Baldassari, J. M. (2011). Effects of quercetin on exercise potential and exercise-induced cytokines in the horse [Unpublished master’s thesis]. Rutgers, The State University of New Jersey.
  3. Li Y, Yao J, Han C, et al. Quercetin, Inflammation and Immunity. Nutrients. 2016;8(3):167. Published 2016 Mar 15. doi:10.3390/nu8030167
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  7. Shi T, Bian X, Yao Z, Wang Y, Gao W, Guo C. Quercetin improves gut dysbiosis in antibiotic-treated mice. Food Funct. 2020;11(9):8003-8013. doi:10.1039/d0fo01439g
  8. Xu D, Hu MJ, Wang YQ, Cui YL. Antioxidant Activities of Quercetin and Its Complexes for Medicinal Application. Molecules. 2019;24(6):1123. Published 2019 Mar 21. doi:10.3390/molecules24061123
  9. Riva A, Ronchi M, Petrangolini G, Bosisio S, Allegrini P. Improved Oral Absorption of Quercetin from Quercetin Phytosome®, a New Delivery System Based on Food Grade Lecithin. Eur J Drug Metab Pharmacokinet. 2019;44(2):169-177. doi:10.1007/s13318-018-0517-3
  11. Wein, S., & Wolffram, S. 2015. A two-week quercetin supplementation in horses results in moderate accumulation of plasma flavonol. Journal of Equine Veterinary Science, 35(7), Abstract, 617-621.

The contents of the BioStar blog are for information purposes only. They are not meant to be a diagnosis, treatment, or other substitute for veterinary advice. Your veterinarian is an integral part of your wellness team and we are proud to work alongside them to support your horse.

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