Decaffeinated tea is not completely caffeine-free, most decaffeinated teas contain about four milligrams of caffeine per cup compared to the average cup of black tea that contains 40 milligrams of caffeine.
For comparison's sake: a cup of filter coffee has 865 milligrams of caffeine.
Many "herbal teas" on the market today do not actually contain the leaves of the Camellia sinensis plant and are therefore not real teas and also will not provide all the health benefits of real tea leaves.
It is recommended that you should drink at least 5 cups of tea a day. This amount of tea, scientists say, boosts the immune system and gives the body a better chance of fighting off infections.
Remember though that instant, bottled, decaffeinated, highly processed or herbal teas do not count because they do not have the same antioxidant properties of green, black, and oolong teas.
Researchers at the Food Safety and Toxicology Center of Michigan State University found that the perfect brewing temperature of tea is 80 degrees Celsius, anything less won't extract the same levels of polyphenols, and anything more will damage the polyphenols with too much heat.