According to Katherine Tallmadge, the American Dietetic Association spokeswoman, “There doesn’t seem to be a downside to tea.”
However, tea contains oxalic acid which if consumed in excess can create problems for the kidneys, including kidney stones. So you may want to stick to 2-3 cups a day if you are susceptible to kidney stones and eating high quantities of high-oxalate foods.
As when drinking more than 1 or 2 servings of any caffeinated beverage, pregnant or breastfeeding women and people taking medicine for high blood pressure (and other such complex medications) should consult their doctor.
People at risk of esophageal cancer should avoid drinking very hot beverages in general, so it is generally good advice to wait 4 minutes before consuming tea.
People with iron deficiencies should be aware that tea can interfere with iron absorption, ironically, by the exact same mechanism that it helps defend the body from free radicals: by chemically bonding with iron during digestion, causing it to be flush out of the body as a waste product.
Also, the same components in tea that yield its health benefits tend to be colorfully pigmented, so observing normal oral hygiene can be important to prevent possible teeth stains.
Men should perhaps limit themselves to less than seven cups of tea per day because one study reported a possible link with prostate cancer.
And of course, tea is just one aspect of a healthy lifestyle. For optimum health, you’ll still need to eat a well-balanced diet, exorcize, get enough sleep, etc.