Though generally considered safe to drink, tea can cause skeletal fluorosis when consumed in very large amounts, according to the New England Journal of Medicine. The caffeine content in tea can decrease iron absorption in people with anemia, though healthy individuals are not at risk, notes the National Institutes of Health. Tea also contains lead in amounts that may be unsafe for pregnant or lactating women to consume, says the Journal of Toxicology.
Though it is often touted as a health beverage, there is little evidence that drinking tea prevents cancer, according to Nature.com. However, drinking three or more cups of black tea a day has been shown to reduce the risk of coronary heart disease. When consumed in moderate quantities of fewer than 8 cups per day, the negative health effects of tea are negligible.
The adverse health effects of drinking tea only occur in healthy individuals when tea is consumed in excessive and unusual amounts, according to the New England Journal of Medicine. Skeletal fluorosis, for instance, may occur in people who regularly consume upwards of 100 tea bags per day, but the fluoride content of tea is not high enough to cause detrimental effects in people who only consume a few tea bags every day.