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. Tea leaves contain diverse polyphenols, includingflavonoids, epigallocatechin gallate (commonly noted as EGCG) and other catechins.
It has been suggested that green and black tea may protect against cancer or other diseases such as obesity or Alzheimer's disease, but the compounds found in green tea have not been conclusively demonstrated to have any effect on human diseases. One human study demonstrated that regular consumption of black tea over four weeks had no beneficial effect in lowering blood cholesterol levels.