Wednesday, December 17, 2008

Allergies and Quercetin

No component of food has a greater effect on allergy than quercetin. This flavonoid compound is found in a wide variety of vegetables and herbs. It stops inflammation caused by the neutrophils. It blocks the action of hyalouronidase, an enzyme that breaks down collagen in the linings of the walls of capillaries so that they can leak fluid and cause swelling around a point of allergic irritation. Keeping collagen intact stops mast cells from releasing their packets of histamine, without having any effect on the nervous system.

To recognize the foods that are the best sources of quercetin, it helps to understand the role of quercetin in plant physiology. Plants don’t rev up their quercetin factories in the hope some allergy-suffering animal will find them and eat them. The role of quercetin in the plant is to store sugars.

Specifically, quercetin acts as an antioxidant in a process related to photosynthesis. Quercetin helps young, growing leaves and shoots store the sugars they need for further growth. Older, tough, woody stems have already accumulated sugars from photosynthesis and produce far less quercetin. Tough greens contain little quercetin. Tender greens contain a maximum of quercetin.

Just as quercetin is more abundant in younger plants than in older plants, some foods contain much more quercetin than others (see the list below). Some relatively uncommon foods, such as lovage leaves, dock leaves, cowberries, and sweet potato greens, contain as much quercetin in a single serving as you would get in a quercetin capsule. Other, more familiar foods contain less quercetin but more than enough to have an effect on allergies.

High-quercetin foods include yellow wax peppers (preferably eaten raw), onions (preferably eaten cooked), buckwheat (cereal better than flour), Serrano peppers, apples eaten with skin, raw spinach, and both green and black tea. Eating at least two servings of any plant food listed in Table 1 every day will provide you with enough quercetin to take the edge off your allergies, but the more enriched sources are more effective.

Quercetin Content of Selected Foods (mg per 100 g serving)

Saw-thistle 16.00
Apples, with skin 4.42
Apples, without skin 1.50
Applesauce, unsweetened, no additives 2.00
Beans, green, snap, raw 2.73
Beans, green, snap, cooked 1.25
Bee pollen 20.95
Bilberries, raw 3.04
Bilberries, cooked 0.60
Blackberries, raw 1.03
Blueberries, frozen 3.93
Blueberries, raw 3.11
Whortleberries, frozen 17.70
Buckwheat 23.09
Buckwheat flour 3.53
Buckwheat cereal 5.84
Cherries, sweet, canned 3.20
Cherries, sweet, raw 1.25
Chokeberries, frozen 8.90
Cilantro, raw 5.00
Corn poppy leaves 26.30
Cowberries, raw 21.00
Cranberry juice cocktail, bottled 1.13
Cranberry juice, pure 16.41
Dock leaves, raw 86.20
Elderberries, raw 42.00
Hartwort leaves, raw 29.30
Lemon juice, bottled 0.00
Lemon juice, fresh squeezed 0.28
Lemons, flesh, without peel 2.29
Lingonberries 12.16
Lingonberry juice 1.02
Lovage leaves 170.00
Onions, boiled, drained, without salt 19.36
Onions, raw 13.27
Onions, red, raw 19.93
Scallions, raw, tops 14.24
Peppers, Ancho 27.60
Peppers, Hungarian 0.51
Peppers, chile, green, raw 16.80
Peppers, wax, yellow, raw 50.63
Peppers, jalapeño, raw 5.07
Peppers, Serrano, raw 15.98
Peppers, sweet (bell), green 0.65
Spinach, raw 4.86
Sweet potato leaves, raw 20.54
Tarragon, fresh 10.00
Tea, green, brewed 2.69
Tea, black, brewed 1.00
Tea, instant, powdered, with sugar 0.34
Tea, instant, powdered, without sugar 0.87

If you take quercetin capsules, you need a vastly larger dose of quercetin than you could ever get from food. The 1,500 mg of quercetin in three standard quercetin capsules is equivalent to the quercetin contained in 85 pounds (40 kilos) of fresh apples, 250 pounds (118 kilos) if you ate them peeled. The effect of one fresh apple or one quercetin capsule on your allergies, however, is about the same. How can this be?

The quercetin used in nutritional supplements is not water-soluble (although newer formulations containing quercetin chalcone are slightly water soluble). Most of the massive dose of quercetin in a supplement essentially sinks like a rock through your digestive tract and is never absorbed.

The quercetin in food is bound in the structure of the food, and released as the food is digested. Beneficial microorganisms in your digestive tract convert this quercetin into forms that are bound to proteins and easily transported in your bloodstream.

Read about honey for allergies.

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