Quercetin

Claims, Benefits: Works like an antihistamine, treats allergies, prevents heart disease and cancer.

Bottom Line: Despite some promising preliminary studies, it’s too early to recommend quercetin as a supplement. You have no idea what’s in the bottle you buy; there could be little or no quercetin, or excessive amounts. Quercetin absorption can vary, depending on its source. And no one knows what dose should be taken.

Full Article, Wellness Letter, January 2003:

Quercetin: An Apple a Day

Of the 80-plus supplements included in the Wellness Guide to Dietary Supplements, quercetin consistently ranks as one of the most visited pages. That surprised us, so we decided to see why people are so interested. For many years now this compound—found in apples, tea, red wine, and other foods—has been studied for possible health benefits. Research has been accumulating, and though it is still in its early stages, many people are jumping on the quercetin bandwagon.
Quercetin is an important member of a large group of plant compounds called flavonoids, once thought to be vitamins. Here are some of its potential benefits:

• This plant pigment is an antioxidant, and thus may help fight cell-damaging free radicals. (But like other antioxidants, it may also act as a pro-oxidant—that is, have the opposite effects and actually become a free radical—under some circumstances.)

• Lab studies suggest that it may have anti-cancer effects, help prevent heart disease by reducing the oxidation of LDL ("bad") cholesterol, and act as an antihistamine.

• Specifically, it may help treat or even prevent prostate cancer by blocking male hormones that encourage the growth of prostate cancer cells, according to preliminary laboratory research at the Mayo Clinic. In another study, men with an inflamed prostate (prostatitis) reported reduced urinary symptoms when they took quercetin.

• Population studies have found that people with high intakes of foods containing quercetin and other flavonoids tend to have lower rates of heart disease and lung cancer.

• Several studies have linked a high intake of apples (rich in quercetin and other flavonoids) with improved lung function and a lower risk of certain respiratory diseases, such as asthma, bronchitis, and emphysema.

Second thoughts

That’s all promising, but it’s too early to recommend quercetin as a supplement. First of all, you have no idea what’s in the bottle you buy. There could be little or no quercetin, or excessive amounts. Quercetin absorption can vary, depending on its source. And no one knows what dose should be taken. There have been reports of supplements causing headaches and tingling in arms and legs. Most important, no one knows what long-term adverse effects high doses may have, or how they may interact with medication.

We do think you should get as much quercetin as you can—from foods. Apples, onions, raspberries, black and green tea, red wine, red grapes, citrus fruit, cherries, broccoli, and leafy greens are the way to go. And they offer lots more than just quercetin.

UC Berkeley Wellness Letter, January 2003