Quercetin Blunts Allergies, Asthma Attacks, and Protects Lungs
Allergic responses can range from the merely irritating to the life-threatening. Triggers can involve sources from food (such as peanuts) or the environment (such as pollen). What many people don't realize is that allergy-like responses are responsible for most of the symptoms of asthma and even chronic obstructive pulmonary disease (COPD).
Quercetin powerfully and favorably modifies the allergic response in potentially life-saving ways.
Let's start with allergies, which are produced by "pre-sensitizing" a person to a particular substance (an allergen). Quercetin blocks the allergic response at several points. It suppresses the actions of immune system cells, reducing the amount of the substance called histamine, that accounts for itchy skin, watery eyes, and (more dangerously) loss of blood pressure during serious allergic reactions. Quercetin also impairs the function of certain cell types that lie at the heart of the allergic and autoimmune processes.54 Studies show that for skin allergies (contact dermatitis), quercetin is more effective than the standard drug cromolyn at inhibiting inflammatory cytokine release.55
Food allergies may be particularly responsive to quercetin prevention. Studies show that quercetin blocks intestinal inflammation stimulated by the allergy-related antibodies.56 That can reduce both local discomfort and dangerous systemic symptoms of food allergies.
In one important animal study, quercetin completely blocked the deadly "anaphylactic" response to peanuts in peanut-allergic rats.57 The animals had much lower histamine levels than did control animals, and none of the airway tightening, blood pressure lowering, or blood vessel leakiness seen in controls exposed to peanuts. This study has powerful implications for future study in humans, since peanut allergy is the leading cause of fatal or life-threatening food allergies.57
In asthma, smooth muscles in the airway tubes (trachea and bronchi) constrict excessively in response to an allergic stimulus. Most of the cellular mechanisms involved are similar to those seen in allergies. When those smooth muscles constrict, airways narrow, and breathing becomes difficult. The result is the familiar wheezing sound and need to push air out of the lungs that we see in people suffering from asthma.
Quercetin blunts the allergy-like components of the asthma response.58 It reduces the number and activation of inflammatory immune system cells, cuts histamine levels, and relaxes airway smooth muscle.58-61 In one study, quercetin was at least as effective as standard asthma maintenance medications such as cromolyn and inhaled steroids at reducing the resistance to air flow.62
As we get older, many people with asthma develop a related condition called chronic obstructive pulmonary disease, or COPD. In COPD, chronic inflammation, oxidant stress, and physical damage to the lungs conspire to obstruct airflow. In severe cases, the walls between alveoli (tiny air sacs) break down in the condition known as emphysema, that results in wheezing, labored breathing, and eventually heart disease.
Quercetin in laboratory studies opens up COPD-inflicted airways. It restores normal elasticity of lung tissue and reduces inflammation.63 Just as important, it reduces production of the protein-melting enzymes that dissolve alveolar walls, helping to retain the lungs' normal architecture and function.63
One important additional benefit of quercetin is its ability to interfere with the facial "flush" that many people experience when taking niacin supplements to control cholesterol. Niacin is one of the most effective agents for normalizing cholesterol levels, but because of the "flush" (redness and burning), regular dosing is often skipped due to physical discomfort. In one recent study a daily dose of 150 mg of quercetin reduced symptoms by more than 47%, and the duration of the flush by 56%.64
Quercetin Boosts Immunity, Fights Infection
Quercetin also acts at the other end of the immune system spectrum by boosting the immune response to many common viruses and bacteria. That makes it especially important for older adults whose immunity declines, making them increasingly susceptible to dangerous infections.
Quercetin kills viruses in laboratory dishes, though the mechanisms are not entirely clear.65-67 In one study, quercetin inhibited influenza A virus replication in the laboratory more effectively than the anti-flu drug Tamiflu®.65 In another study, quercetin inhibited hepatitis C virus replication. Hepatitis C is a major cause of liver failure and liver cancers.66 Finally, quercetin blocked replication of the rhinovirus, the virus responsible for the common cold.67
Not surprisingly, then, quercetin-supplemented animals display fewer symptoms and greater survival in the face of several different types of virus. Mice infected with influenza A virus, but supplemented with quercetin just before and for six days following infection, had significantly fewer serious symptoms of flu.68 They also survived longer.
In-depth study showed that the animals had an astonishing 2,000-fold lower number of viruses in their lungs; in fact, they had just half of the virus load as did animals treated with Tamiflu®.68
Adults who supplement with quercetin are significantly less likely to develop colds and upper respiratory tract infections following intensive exercise: in one study just 5% of supplemented subjects got sick, while 45% of control patients experienced colds.69 And in a population of middle-aged and older adults who were physically fit, 1,000 mg quercetin/day reduced the number of sick days taken for colds by 31%, and the severity of symptoms by 36%.70
Quercetin is also effective against bacterial infections. It decreased the infection rate and inflammatory response to Helicobacter pylori, the cause of many ulcers and eventually cancers of the stomach.71,72 Quercetin also reduced inflammatory responses and strengthened host defenses in experimental Salmonella infections, a major cause of death and disability, especially in older adults.73
Mother Nature protects plant life from the most extreme and harsh environments on our planet. She does it by protecting them with powerful phyto-chemicals, the most common of which is quercetin. Fortunately, that protective effect is readily transferred when we consume quercetin ourselves. Quercetin extends animal life spans, in large part by protecting us against the same general threats that plants face: oxidant stress, DNA damage, and environmental toxins. A rapidly expanding body of scientific evidence now links high quercetin consumption to improved cardiovascular health, reduced cancer risk, milder allergic responses, and improved resistance to infection. Getting enough plant-based nutrients is a major problem for most people; fortunately, it is easy to boost your quercetin intake with highly bioavailable supplements.
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