On page 291, he writes about tannins – ” Most herbs contain tannins, substances that bind up proteins and in so doing provide the property of being astringent. There appears to be a correlation between extensive drinking of tannin-rich teas and the occurrence of esophageal and stomach cancer. It is believed that the repeated effect of the tannins on the throat and stomach, especially in combination with other agents in the diet, may result in the formation of cancerous cells. In those countries where black tea (Camellia sinensis) is consumed in large quantities, the rate of esophageal cancer tends to be high. However, where the black tea is commonly taken with milk, the elevated cancer rate is not seen. This is because the tannins are rendered insoluble by the milk, the proteins of the milk being bound to the tannin.”
“One should use astringent teas as needed, but avoid excessive use. When an astringent herb is being used for properties other than astringency, a little milk should be added to neutralize the tannins. There is no reason to fear the occasional use of astringents internally or externally.”
Also, tannins, because of their astringent qualities are used to cure animal hides, because astringents tighten up tissues and cells. So, think of that a bit in reducing your intake of black teas.
So, I thought about this and noticed that alot of South Asians use a small amount of milk in their tea, and I thought, that is so smart. I would recommend green tea alot more than black tea, but it is your decison, I just wanted to pass on some information that I had learned.