Black coffee, without added cream or sugar, is thought to be the healthiest form of the beverage, but like anything else, consuming too much can be unhealthy. The main ingredient in coffee is caffeine, which has well-documented health risks in large doses, according to WebMD. Additionally, while drinking a cup or two of coffee daily can invigorate the mind and prepare a person for their day, too much coffee and caffeine can cause excessive tension.
Caffeine is a stimulant and a diuretic. It stimulates the adrenal glands to produce cortisol, a hormone responsible for stress. This puts strain on the heart and cardiovascular system and can exacerbate high blood pressure. Drinking no more than four 8-ounce cups of black coffee per day can help prevent this. As a diuretic, caffeine can cause excessive urination, which can lead to dehydration if the water is not replenished.
Black coffee is often acidic and the caffeine causes production of hydrochloric acid in the stomach. When the esophagus relaxes, this allows stomach acid to travel into the esophagus, potentially causing heartburn. Therefore, it's best to eat breakfast first, as to not have coffee on an empty stomach.