It is widely believed that tea originated in the Far East and was introduced to the Western world in the 19th century. Just like coffee, tea is acidic; therefore those with sensitive stomachs are advised to watch how much they drink.
Acidity in tea comes from the tannins it contains and can be tasted if a teabag is left to brew for too long, leaving an acrid, bitter flavor. Its acidity derives from the soil in which the tea plants are grown, as they can't survive on soil that is too alkaline.
Black teas have the highest acidity content, between pH 4.0 to 6.0 (anything lower than 7 is deemed to be acidic), while green and oolong varieties have lower levels. It is believed the practice of adding milk to tea started because it reduces the acidity levels.
Having a diet high in acidic foods can cause health problems such as gout, weight problems, ulcers, bloating, fatigue, a tendency to get infections, and even problems such as depression and apathy.