Dietary iron can rob green tea of its benefits arising from its antioxidant property. A Penn State research on a mouse model found that green tea's polyphenols lose their healing ability when bound to iron.

"If you drink green tea after an iron-rich meal, the main compound in the tea will bind to the iron," said Matam Vijay-Kumar, assistant professor of nutritional sciences, Penn State. "When that occurs, the green tea loses its potential as an antioxidant. In order to get the benefits of green tea, it may be best to not consume it with iron-rich foods."

Iron-rich foods like red meat and dark leafy greens, as well as iron supplements have this negative influence on green tea.

Polyphenol EGCG (epigallocatechin gallate) -- the main compound in green tea – when bound to iron loses its ability to inhibit an enzyme responsible for inflammation. Inactivation of the enzyme myeloperoxidase by EGCG usually helps control inflammatory bowel disease(IBD).

Often, IBD patients are prescribed iron supplements. The team also found that EGCG is inactivated by a protein found in inflammatory conditions.

"The benefit of green tea depends on the bioavailability of its active components," said Beng San Yeoh, graduate student in immunology and infectious diseases and first author of the study. "It is not only a matter of what we eat, but also when we eat and what else we eat with it."
The study is published in the American Journal of Pathology.

Chronic inflammation of the digestive tract in IBD results in bloody diarrhoea, pain, fatigue, weight loss and other symptoms including iron deficiency/anemia.

Polyphenols in green tea block a signalling molecule called VEGF, which often triggers atherosclerosis and cancer. EGCG has also been seen to generate nitric oxide in the blood, which helps widen the blood vessels and prevent damage. It has also been seen to trigger a process in the mitochondria causing the death of oral cancer cells.

Green tea made from unfermented leaves contains the highest concentration of powerful antioxidants in its six polyphenols, of which EGCG is one. Antioxidants fight free radicals that can damage DNA and cause cell death.