To Your Health

I want to try supplementing with quercetin to help my allergies. How much should I take?

Q. I want to try supplementing with quercetin to help my allergies. How much should I take? I've heard it's hard to absorb.

A. Quercetin is one of a great number (5,000 or more) of water-soluble plant pigments called flavonoids that provide much of the flavor and color in fruits and vegetables. Humans cannot synthesize quercetin or the other flavonoids, but they reportedly have a wide variety of beneficial health effects. Quercetin can be found most abundantly in apples, onions, tea (black or green), berries, grapes, broccoli, cauliflower, and cabbage, as well as many seeds and nuts. It is also available in pill form. When used as a food supplement, 600 milligrams a day is a common dose, but double that amount seems entirely safe. Studies in animals and humans indicate that most bioflavonoids are not very well absorbed, although there is growing evidence from human feeding studies that the absorption of quercetin is as much as 10 times higher than originally believed.

Most of the flavonoids present in plants are attached to sugars and are absorbed in that form. There is considerable controversy in the scientific community over whether flavonoids bound to sugar have as much biological activity as the "free" or unbound flavonoids. Some recent research may make the discussion moot, because it appears that bacteria in the intestine are very good at separating flavonoids from the attached sugar, increasing its biological activity over the "bound" form.

Quercetin inhibits both the production and release of histamine by immune cells. Histamine elevation is responsible for much of the discomfort we associate with an allergic reaction, so it makes sense to use it as an antihistamine. There are several other circumstances where quercetin might be worth a try. Quercetin is an antioxidant, protecting LDL cholesterol (the "bad" cholesterol) from the oxidative damage that leads to plaque formation. In addition it prevents blood clots and promotes relaxation of the heart muscle, which reduces the risk of stroke and lowers blood pressure. Quercetin can also significantly inhibit formation of keloid scars by limiting (temporarily and reversibly) cell growth after an injury.

There are several other nutrients that will help allergies, healing, and circulation, but quercetin has a unique potential. Quercetin, in common with certain medications used to treat acquired immunodeficiency syndrome, is a "reverse transcriptase inhibitor." The AIDS virus is a "retrovirus," and unlike our body cells it passes its genetic material on to its offspring in the form of RNA rather than DNA. After infecting a host, its RNA must be converted to DNA in order to use the host's cellular machinery to reproduce. This process requires an enzyme known as reverse transcriptase. Our bodies have almost no use for this enzyme so stopping its action has little effect on us but is crippling to the AIDS virus. As yet, no research has confirmed the possibility that quercetin hinders AIDS virus replication, but perhaps the difficulties with absorption mentioned above may need to be overcome before there are positive results.

The tremendous safety of a nutrient such as quercetin, with so many useful biological activities, certainly justifies further research.

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