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Quercetin (polyphenol)

Updated: 2025-10-09

Overview

Quercetin is a flavonoid found in many plants (onions, apples, capers, green tea).
It has mild antioxidant and anti-inflammatory properties, studied in metabolic, cardiovascular, and immune contexts.
Clinical results are variable, often modest, and highly dependent on dose, form, and bioavailability.

🟢 Proven Effects

  • May slightly reduce inflammatory markers (CRP, IL-6) in certain metabolic-risk groups.
  • Shows antioxidant activity on lipids and oxidative stress.
  • Some studies suggest a modest reduction in frequency or duration of respiratory infections.
  • Good tolerance profile at usual doses (< 1 g/day).

🟡 Unclear Areas

  • Clinical outcomes vary widely depending on dose, duration, and formulation (limited absorption).
  • Preventive efficacy (immunity, infection, athletic performance) remains inconsistent across studies.
  • Potential roles in blood sugar and blood pressure regulation are still uncertain due to low-powered trials.

🔴 What It Doesn’t Do

  • Does not replace dietary antioxidants or anti-inflammatory foods (fruits, vegetables, tea).
  • Does not “boost” immunity in a significant or lasting way.
  • No proven anticancer effects in humans.

Intake & Dosage (non-prescriptive)

  • Typical dose: 250–1000 mg/day, split into 1–2 servings.
  • Often combined with bromelain to enhance absorption.
  • Take with a meal containing some fats.
  • Rich food sources: red onions, capers, apples, berries, green tea.

💣 Upper Limit (UL)

Note: No known toxicity at dietary intakes.
Human studies indicate good tolerance up to 1 g/day.
Above this, long-term safety is poorly documented, especially for liver and kidney function.

Safety

  • Well tolerated at normal intakes.
  • Mild headaches or nausea may occur.
  • Exercise caution with sensitive drug metabolism (CYP3A4, CYP2C9, transporters).
  • Pregnancy/breastfeeding: insufficient data → avoid concentrated supplementation.

⚠️ Risks & Interactions

  • Generally well tolerated; possible mild headaches or digestive discomfort.
  • Prolonged high doses: use caution with liver/kidney sensitivity.
  • ⚠️ May affect certain metabolic enzymes (CYP/transporters) → caution with drugs that have a narrow therapeutic window.
  • Avoid combining excessive amounts with other concentrated polyphenol extracts.

✅ Quality Tips

  • Choose phytosomal or liposomal forms for better absorption.
  • Check purity (>95% quercetin) and actual dose per capsule.
  • Avoid “miracle blends” that are underdosed or unstandardized.
  • Always combine with a plant-rich diet full of colorful fruits and vegetables.

Sources

⚠️ Educational information. Always seek professional advice.