Quercetin
Quercetin
Quercetin is a naturally occurring flavonoid polyphenol found in foods such as onions, apples, berries, and green tea, widely used as a dietary supplement for its antioxidant, anti-inflammatory, and potential immune-modulating properties. It is commonly studied and used for conditions including allergic rhinitis, exercise-induced inflammation, cardiovascular support, and more recently as a senolytic agent to clear senescent cells. Research also supports its role in enhancing bioavailability of other compounds like zinc, contributing to its use in antiviral and longevity-focused supplement stacks.
Mechanism of Action
Quercetin inhibits pro-inflammatory enzymes including cyclooxygenase (COX) and lipoxygenase (LOX), and suppresses the NF-κB signaling pathway, reducing production of inflammatory cytokines such as TNF-α and IL-6. It acts as a potent free radical scavenger and chelates transition metals, limiting oxidative stress, while also stabilizing mast cells to inhibit histamine release relevant to allergic responses. As a senolytic, quercetin inhibits anti-apoptotic pathways (including PI3K/AKT and BCL-2 family proteins) selectively in senescent cells, facilitating their clearance.
Evidence by Health Goal(18 goals)
Dosing Protocols
With meals containing fat to improve absorption
Phytosome or EMIQ (enzymatically modified isoquercitrin) formulations offer significantly better bioavailability than standard quercetin powder. For senolytic use, higher doses of 1000-1500mg may be taken intermittently (2 consecutive days per week or month) rather than daily. Standard quercetin has poor oral bioavailability (~1-2%), making formulation choice critical.
Safety & Side Effects
Quercetin is generally considered safe at typical supplemental doses (500-1000mg/day) with a favorable short-term safety profile supported by human clinical trials; however, long-term high-dose use warrants caution due to theoretical nephrotoxicity from oxalate metabolites and significant inhibition of cytochrome P450 enzymes (CYP3A4, CYP2C9) that can alter the metabolism of many common drugs. It is not a controlled substance and is available over-the-counter globally, but individuals on prescription medications should consult a healthcare provider before use.
Possible Side Effects
- !Gastrointestinal discomfort including nausea, bloating, or stomach cramping at doses above 1000mg
- !Headache, particularly during initial use
- !Tingling sensations in the extremities reported at higher doses
- !Kidney damage risk with very high doses (>1g/day long-term) due to oxalate metabolites
- !Potential pro-oxidant effects at supraphysiological doses in sensitive individuals
- !Drug interactions leading to altered plasma levels of co-administered medications
Interactions
- -Inhibits CYP3A4 and CYP2C9 enzymes - can significantly increase plasma levels of cyclosporine, statins, benzodiazepines, and many other CYP-metabolized drugs
- -May potentiate anticoagulant effects of warfarin and other blood thinners, increasing bleeding risk
- -Enhances intracellular zinc uptake - often deliberately co-administered with zinc as a zinc ionophore
- -Can reduce absorption of certain antibiotics (e.g., fluoroquinolones) if taken simultaneously - separate by at least 2 hours
- -Additive blood pressure lowering effects possible when combined with antihypertensive medications
Cost & Where to Buy
Standard quercetin powder or capsules are inexpensive ($15-25/month), while enhanced bioavailability formulations such as quercetin phytosome (Quercefit) or EMIQ can cost $40-60/month. Price varies considerably by dose, brand quality, and formulation type.
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