Q. What is yerba mate, and what are its pros and cons for my health?

A. Yerba mate, also known as Ilex paraguariensis, is a small tree or shrub that grows in parts of Argentina, western Uruguay, southern Brazil and eastern Paraguay. It has been used for generations as a tea, made by steeping the plant's dry leaves and twigs. Popular in South America for its stimulating effects, it is now being sold in the United States as yerba mate (say yair-ba MAH-tay) tea.

Researchers have found that yerba mate does not contain caffeine per se, but does contain caffeine-like compounds known as xanthines. Although yerba mate tea products are frequently labeled as "caffeine-free," some might argue that this is a bit misleading, since xanthines are in the same family as caffeine. People who drink yerba mate tea often report that it increases their mental alertness without inducing as much of the revved-up, stimulating feeling that they experience with caffeinated beverages like coffee or black tea.

Yerba mate may have several health benefits, but it may also pose some health risks. Many studies support its anti-cancer, antioxidant and anti-obesity effects, but conflicting research suggests possible links to cancer.

In 2005, an article in the Journal of Clinical Nutrition reported that yerba mate's antioxidant properties can help patients who have suffered heart attacks.

The journal Cancer Investigation, in a 2007 article titled "Carcinogenic Food Contaminants," listed yerba mate as an agent with a moderate level of carcinogenicity (or cancer-causing potential). Later that year, the Journal of Food Science reported that yerba mate has been shown to lower cholesterol, prevent liver damage, benefit the cardiovascular system, protect DNA from oxidation and may help in obesity management. According to the article, however, "it has also been reported that yerba mate tea is associated to both prevention and the cause of some types of cancers."

In May 2008, the journal Cancer Epidemiology reported that high concentrations of a type of carcinogenic compound were found in yerba mate leaves. Two months later, the journal Mutagenesis reported that the antioxidants found in yerba mate can help protect DNA from damage and enhance DNA repair activity, thus assisting in protection against cancer.

As far as your health is concerned, it appears that yerba mate may be a paradoxical herb with both anti-cancer and pro-cancer effects. Until further research sheds more light on its properties, your best bet is to play it safe and refrain from incorporating yerba mate tea into your daily diet.