The Health Benefits of Quercetin

A guest blog post by holistic writer Andrea Lewis.  Consult with your doctor before making any medical or health decisions.

Quercetin is a crystalline pigment phytochemical/flavonol, found abundantly in whole foods. Quercetin has been studied and utilized for its healing and beautifying benefits for more than a decade now. And quercetin supplements are used to reduce allergic responses and/or boost immunity. Following are some of quercetin's most noted health benefits.

Top 5 Quercetin Benefits

1. Effective antioxidant
2. Prevents the proliferation of mutated cells
3. Lowers cholesterol levels
4. Reduces blood pressure
5. Fights artherosclerosis

Quercetin is considered a powerful antioxidant. Multiple studies have demonstrated quercetin's extraordinary oxidation fighting prowess. And, according to a study published in Advances In Experimental Medicine and Biology, quercetin is even more effective than the much celebrated Curcumin (the active ingredient in Tumeric). After comparing quercetin to curcumin in various tests, the study's authors concluded that “1) Quercetin has a higher reduction potential compared with curcumin at three different pH settings and is comparable to Trolox [an antioxidant like vitamin E] at pH 7-9.5; 2) its [total antioxidant capacity] is 3.5 fold higher than curcumin...”1

Quercetin's antioxidant ability has been linked to its ability to protect cells from mutation. Quercetin is considered a “strong reducing agent”2, which means it donates an electron to prevent the oxidation of cells, and “together with other dietary reductants such as vitamin C, vitamin E, and carotenoids protect body tissue against oxidative stress.” Recent studies have suggested that quercetin's antioxidant actions improve normal cell survival and induces apoptosis (the process of programmed cell death) in mutated cells, preventing their proliferation.

Quercetin has also been shown to lower cholesterol levels, reduce blood pressure, fight artherosclerosis and improve overall cardiovascular health. According to an article published in Life Extension, “In a study of 805 men aged 65-84 years, those with the highest quercetin and other flavonoid intake were 68% less likely to die from coronary heart disease than those with the lowest intake. A similar study found a reduction in death rates from all causes of 31% for women and 24% for men, with a 46% reduction in coronary death rates for women and a 22% reduction for men in those with the highest intakes.

“This dramatic cardiovascular protection is the result of a concerted synergy between several basic quercetin mechanisms, including its ability to lower cholesterol and reduce dangerous accumulations of abdominal and liver fat.

“In one study on quercetin's impact on cholesterol levels, a group of otherwise healthy male smokers took 100 mg/day of quercetin or a placebo for 10 weeks, with blood tests done at baseline and at the end of the study. The supplemented group, but not the placebo group, had significant reductions in total and LDL cholesterol, and an increase in HDL cholesterol. They also had a significant reduction in blood sugar, another cardiovascular risk factor.”3

The journal Artherosclerosis published a study that proved quercetin was effective for fighting atherosclerosis. The study concluded that “Quercetin reduces the expression of human [C-reactive protein] and cardiovascular risk factors ([serum amyloid A, and the drug] fibrinogen) in mice in vivo. These systemic effects together with local anti-proliferative and anti-inflammatory effects in the aorta may contribute to the attenuation of atherosclerosis.”4

Quercetin-rich Foods

• White onions – 21.42mg/3.5 oz.
• Red onions – 33.4mg/3.5 oz.
• Black plums – 12.5mg/3.5 oz. 
• Cranberries – 15.09mg/3.5 oz.
• Kale – 7.71mg/3.5 oz.
• Blueberries – 5mg/3.5 oz.
• Chives – 4.77mg/3.5 oz.
• Pear – 4.51mg/3.5 oz.
• Apples – 4.27mg/3.5 oz.
• Sweet cherries – 2.64mg/3.5 oz. 
• White currants – 2.68mg/3.5 oz.

If a food is brightly colored, and even if it's not (white onions and currants), chances are it contains quercetin. Obviously, the listed whole foods are not the only ones to contain quercetin, but they do contain the most. Some beans (Fava beans/broad beans), broccoli, leeks and red grapes are also known to contain quercetin. So, if you eat a diet rich in technicolored foods you can be certain that you are getting your fair share of quercetin, despite claims to the contrary.

How Much Quercetin Do We Need?

Unfortunately, there is no recommended daily allowance (RDA) for Quercetin or any other phytonutrient. The same goes for adequate intake (AI) and upper intake limits (UL). Quercetin is one of the most abundant phytonutrients, but there's only so much quercetin you can consume by eating foods; because you can only eat so much food.

That being said, vegans have a definite advantage as it regards quercetin consumption. While the average person's intake of quercetin from food sources “ranges from five to 40 milligrams per day, [it] could be as much as 200-500 milligrams per day when consumption of fruits and vegetables is high, especially when the peel of the fruit is consumed.”5 Since a vegan's whole diet is composed of whole foods, vegans undoubtedly get even more quercetin in their diets.

Quercetin Drug Interactions

According to WebMD, taking quercetin supplements may decrease the effectiveness of some antibiotics, particularly Quinolone antibiotics. “Some scientists think that quercetin might prevent some antibiotics from killing bacteria. But it's too soon to know if this is a big concern.”6

Medications that are changed and broken down by the liver also interact with quercetin. Quercetin may decrease how quickly the drugs are broken down by the liver, and increase the effects and side-effects of the medications. The diabetes drug Avandia, immunosuppressant Cyclosporin, antidepressants Paxil and zoloft, psychotropic drugs Haldol and Risperdal, the proton pump inhibitor Prilosec, antihistamine Allegra and many more such drugs.

Quercetin also interacts with medications moved by pumps in cells. “Quercetin might make these pumps less active and increase how much of some medications get absorbed by the body. This might cause more side effects from some medications.”6 The heart medications Digoxin and Quinidine, the proton pump inhibitor Zantac, and antifungal antibiotic Nizoral are all members of this group. Allegra is on this list as well.

This probably seems like an extensive list of medications that you would have to avoid, because of one nutrient (and what I've mentioned here isn't even half of them); however, these interactions only occurred when one used quercetin supplements. The quercetin found in whole foods have no proven drug interactions.

Natural is better

The gist of all this is, natural nutrition really is better. And quercetin is yet another health promoting benefit of eating a diet rich in whole foods, whether you are a full-on vegan, vegetarian or none of the above.

Just keep in mind that boiling causes more quercetin loss than frying, but microwaving (without water) is the cooking method that preserves nutrients the best. Go figure. In addition, “The hydrolysis of quercetin glycosides for daily cooking might occur with the addition of seasonings such as glutamic acid. Additional ferrous ions accelerated the loss of flavonoids.”7 So, overall, you will get more quercetin in your diet if you eat your whole foods raw and unseasoned.


References:

1 Zhang M, Swarts SG, Yin L, et al. “Antioxidant properties of quercetin”. Advances In Experimental Medicine and Biology, 2011. Web. October 13, 2015

2 Jan AT, Kamli MR, et al. “Dietary Flavonoid Quercetin and Associated Health Benefits – An Overview”. Food Reviews International, volume 26, issue 3, 2010. Web. October 10, 2015

3 Buckley, Anne. “Quercetin: Broad-Spectrum Protection”. Life Extension, September 2012. Web. October 12, 2015

4 Kleemann R, Verschuren L, et al. “Anti-inflammatory, anti-proliferative and anti-atherosclerotic effects of quercetin in human in vitro and in vivo models”. Artherosclerosis, September 2011. Web. October 14, 2015

5 “Quercetin”. Human Performance Resource Center, n.d.. Web. October 14, 2015

6 “Quercetin: Uses, Side Effects, Interactions and Warnings”. WebMD, n.d.. Web. October 13, 2015

7 Ioku K, Aoyama Y, et al. “Various cooking methods and the flavonoid content in onion”. Journal of Nutritional Science and Vitaminology, February 2001. Web. October 14, 2015

Heneman K, PhD, Zidenberg-Cherr S, PhD, et al. “Some Facts About Flavonols”. Nutrition and Health Info-Sheet, October 2008. Web. October 11, 2015.

Kerns, Michelle. “Foods With the Highest Content of Quercetin”. Livestrong, April 30, 2015. Web. October 13, 2015