- Li H et al, 2003, Review in the studies on tannins activity of cancer prevention and anticancer PubMed
- Aviram M et al, 2001, Pomegranate juice consumption inhibits serum angiotensin converting enzyme activity and reduces systolic blood pressure PubMed
- Kaltwasser JP et al, 1998, Clinical trial on the effect of regular tea drinking on iron accumulation in genetic haemochromatosis PubMed
- Tannins: fascinating but sometimes dangerous molecules Cornell University
- Iron Linus Pauling Institute
- Brune M et al, 1989, Iron absorption and phenolic compounds: importance of different phenolic structures PubMed
- Beecher GR, 2003, Overview of Dietary Flavonoids: Nomenclature, Occurrence and Intake The Journal of Nutrition
Tannin is any polyphenolic compound that forms strong complexes with proteins and other large molecules . The word tannin originates from “tanning”, a leather production by soaking animal skins in plant extracts containing tannins . Tannins are polyphenols that give bitter taste and mouth-drying effect to the plant foods.
- Hydrolyzable tannins are esters of gallic acid (gallotannins) or ellagic acid (ellagitannins) and sugars.
- Non-hydrolyzable or condensed tannins or proanthocyanidins consist of flavan-3-ols. They include procyanidins, and prodelphinidins.
- Derived tannins formed during food processing such as theaflavins and thearubigins in black tea or oolong tea.
- Tannic acid extracted from nutgalls.
- Reference: [4,7]
Foods High in Tannins
- Red wine
- Green tea, black tea, oolong tea
- Chocolate, cocoa
- Unripe fruits: pomegranate, persimmon
- Berries: strawberries, cranberries, blueberries
- Apples with skin
- Grapes, especially grape seeds and skins
- Nuts: hazelnuts, walnuts, pecans
- Spices: cloves, thyme, cumin, vanilla, cinnamon
- Beans: red beans, acacia
- Smoked fish and meat
- Reference: 
Tannins as Food Additives
Tannic acid is used as a clarifying agent or dye in fruit juices, soft drinks and alcoholic drinks.
Various non prescription (over-the-counter) oral tannin supplements are available.
Tannins Health Benefits
There is INSUFFICIENT EVIDENCE about the effectiveness of tannins in the prevention or treatment of cancer  or high blood pressure  and hemochromatosis .
Tannins Safety: Side Effects, Toxicity
Side effects may include nausea, vomiting, diarrhea.
Tannins ingested in large amounts may reduce the absorption of the non-heme iron from plant sources, not iron from animal foods . Tannins may reduce the absorption of certain medications.