Quercetin: a protective pigment

Quercetin acts as a pigment in many fruits and vegetables, such as grapes, apples, kale, broccoli and onions, as well as green and black tea and red wine. The substance, from a group of compounds called flavonoids, is marketed as a powerful antioxidant that may help prevent cancer and heart disease, lower cholesterol and act as an antihistamine.

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Uses: Supplement makers say quercetin protects against heart attacks, strokes, cancer and diabetic complications. It’s also sometimes used for staving off allergic reactions.

Dose: 200 to 1,200 milligrams a day in pill form, usually taken in separate doses before meals. Many doctors and nutritionists recommend obtaining quercetin from foods, as little research has shown what dose , if any, is effective or safe in supplement form.

Precautions: Quercetin may hinder the effectiveness of some antibiotics or cause headaches and limb tingling. Little is known about the supplement’s short- and long-term safety.

Research: Most research comes from animal and laboratory studies, which suggest that the compound may lower cholesterol and protect against cancer. Little evidence supports its use against strokes or diabetic conditions, although the substance has been shown to hamper inflammation and the release of histamine. Other studies have shown that people who eat diets rich in flavonoids decrease their risk of cancer and heart disease.

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Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.

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-- Elena Conis