Black and green teas contain no essential nutrients in significant content, with the exception of the dietary mineral, manganese at 0.5 mg per cup or 26% of the Daily Value.[69] Tea leaves contain diverse polyphenols, including flavonoids, epigallocatechin gallate (commonly noted as EGCG) and other catechins.[70][71]
It has been suggested that green and black tea may protect against cancer[72] or other diseases such as obesity[73] or Alzheimer's disease,[74] but the compounds found in green tea have not been conclusively demonstrated to have any effect on human diseases.[75][76] One human study demonstrated that regular consumption of black tea over four weeks had no beneficial effect in lowering blood cholesterol levels.