Green tea by itself is a potent source of healthy antioxidants known as catechins. But a new study indicates that adding citrus juice or vitamin C can significantly boost the bioavailability of those compounds, which have been linked to lowered cancer risk as well as improved heart and brain health.
The study by Purdue University researchers, published in the November 2007 Molecular Nutrition and Food Research, involved putting green tea alone and with various additives through a model simulating gastric and small-intestinal digestion. They found that catechins are unstable in non-acidic environments such as the intestines and less than 20 percent of the total remains after digestion. But adding vitamin C (which is done in ready-to-drink products to increase shelf life) increased recovered levels of the two most abundant catechins by sixfold and 13-fold, respectively.
Adding citrus juice to plain green tea was also beneficial. The study found that lemon juice caused a roughly four-fold boost in the recovered levels of catechins; in order, the next most effective juice additions were orange, lime and grapefruit. And one should not be stingy with the juice – while adding 10 percent juice was helpful, the best catechin preservation happened at levels of 20 to 50 percent juice. This suggests that while adding a squeeze of lemon to tea is an excellent idea, it also makes sense to think in terms of 20 to 50 percent blends using orange and grapefruit juices.
Studies have shown catechins from the green tea plant, Camellia sinensis, can inhibit cancer cell activity and stimulate production of immune-strengthening enzymes.The researchers believe that other types of tea, such as black or oolong, would likely also benefit from the addition of juice or vitamin C, because these types also contain catechins, though in smaller amounts than in green tea. .
Dr. Weil’s take: This is an interesting study, full of important implications. First, I am not surprised that adding lemon juice to tea – a popular combination for centuries – appears to be the best practice for health, confirming that time-honored culinary traditions are often ahead of laboratory research. Second, this appears to be one of the rare cases in which a prepared food product such as a bottled or canned tea preserved with vitamin C can compete for health benefits with a fresh, homemade one. Finally, if you like citrus in your home-brewed tea, by all means, squeeze away!