A cup of black tea steeped for four minutes has 40 to 100 milligrams of caffeine, whereas a three minute infusion only contains about 20 to 40 milligrams. A comparable cup of coffee contains 60 to 180 milligrams. Oolongs have even less caffeine and green teas have negligible amounts. On the other hand, over the years, multiple attempts have been made to associate coffee with negative health effects. However, most claims remain unsubstantiated.
Coffee seems to be a relatively safe beverage in moderation.
There are, in fact, some positives to drinking coffee, based on its caffeine content. For example, coffee is probably the most concentrated source of caffeine in our diets. In moderation, caffeine is capable of boosting energy, increasing alertness and quickening reaction time. It is a mood elevator and may help mild depression. For asthmatics, even a single cup of coffee per day has been shown to reduce asthmatic symptoms.