Researchers Question Safety of Some Plant Antioxidants

Researchers in Taiwan warn that some naturally occurring plant antioxidants may actually have carcinogenic properties and represent a health risk that warrants further evaluation.

Investigators at Hungkuang University (Taichung Hsien, Taiwan) and colleagues at other Taiwanese research institutes conducted a series of experiments to test the pro- and anticancer effects of several popular plant antioxidants on the development of kidney cancer in a rat diabetes model.

The primary antioxidants that were evaluated were quercetin and ferulic acid. Ferulic acid is found in seeds of plants such as in rice, wheat, and oats, as well as in coffee, apple, artichoke, peanut, orange, and pineapple. It can be extracted from wheat bran and maize bran using concentrated alkali. Foods rich in quercetin include black and green tea, capers, lovage, apples, onion, especially red onion, red grapes, citrus fruit, tomato, broccoli and other leafy green vegetables, and a number of berries including cherry, raspberry, bog whortleberry, lingonberry, cranberry, chokeberry, sweet rowan, rowanberry, sea buckthorn berry, crowberry, and the fruit of the prickly pear cactus.

The investigators induced diabetes in a rat population for a 28-week period with the drug streptozotocin. At the end of this period, the animals were treated with either quercetin or ferulic acid. Results published in the July 29, 2010, online edition of the Journal of Agricultural and Food Chemistry revealed that in addition to various noncancerous types of kidney damage, the treated animals developed aggressive forms of kidney cancer.

This finding led authors to conclude that, "In this study we report that quercetin aggravated, at least, if not directly caused, kidney cancer in rats. Some researchers believe that quercetin should not be used by healthy people for prevention until it can be shown that quercetin does not itself cause cancer.”

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