Tannic acid

Tannic acid is a naturally occurring plant polyphenol and can be found in practically all aerial plant tissues. Mainly used in industry as a fixative of dyes and as a chemical intermediate and reagent in the manufacture of leather, inks, coatings, and rubber. Tannic acid has been used in medicine to form protective coverings on tissue wounds. Historical medicinal applications of tannic acid include as anti-hemorrhoidal, anti-diarrheal and for treatment of skin burns, skin sores and ulcers. Recently, novel pharmacological uses of tannic acid have been explored including as antioxidant, anti-cancerous, anti-allergic, anti-inflammatory, anti-helminthic and anti-microbial agent. Tannic acid can form complexes with nutrients including carbohydrates, proteins and essential minerals. Tannin-nutrient complexes are indigestible are excreted. By reducing nutrient bioavailability, tannic acid reduces the nutritional value of foodstuffs. Tannic acid also forms complexes with enzymes that are involved in nutrient digestion and absorption. Tannic acid-enzyme complexes cannot fulfill their enzymatic and catalytic functions upon nutrients and this in turn are responsible for lowering the nutritional quality of foodstuffs. For these reasons, tannic acid is considered to be an antinutrient. Consumption of too much tannic acid can lead to malnutrition and diseases such as anemia, osteoporosis and cancer. An unusually high incidence of esophageal cancer has been noted in areas where nuts and seeds rich in tannins are consumed. A positive relation has been observed between the food tannin content and the incidence of esophageal cancer.