There is no such thing as efficacy of black tea as a food. But its vitamins and other nutrients can provide the body needs. Black tea is made from the fresh leaves or mature tips of the tea tree, through the greening, kneading, stacking, drying and other processing techniques, to the black color, tea color orange, pure aroma for the best. Black tea contains vitamins, minerals, proteins, amino acids, caffeine, tea polysaccharides and other substances. Every 100 milliliters of black tea water contains 1 calorie, which contains 5 micrograms of folic acid, 99.7 grams of water, 37 milligrams of potassium and 3 milligrams of magnesium. Black tea contains tea polysaccharide, which is beneficial to the body. Black tea contains caffeine, which has a certain refreshing effect, so insomniacs should consume less. Black tea should not be consumed too much at one time, so as not to cause discomfort.