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Green tea can decrease your body's ability to absorb iron. The catechins in the tea block some of the iron from being absorbed in your body.  Know the risks. If you have anemia, drinking green tea can make it worse.  Iron-deficiency anemia is caused by not having enough iron in the blood, which in turn lowers either the red blood cells or hemoglobin. Anemia can cause fatigue because not enough oxygen is being carried throughout your body. One cause of anemia is excessive menstrual bleeding. If you think you may be anemic, talk to your doctor about taking an iron supplement and eating iron-rich foods. Green tea can increase pressure in the eye for an hour or more.  Know who's at risk. If you suffer from glaucoma, you can increase the risk of the disease. Glaucoma is an eye disease. It affects the optic nerve. It can impair your vision over time. Instead, drink your tea between meals to give your body a chance to absorb the iron.  Eat foods rich in iron and vitamin C. Iron can help with anemia, while vitamin C increases your body's ability to take in iron.  Iron-rich foods include meats, beans, and greens, to name a few.  Foods rich in vitamin C are things like citrus fruits, kiwi, strawberries, broccoli, and peppers. Green tea increases the pressure in your eye within 30 minutes of drinking it, and the effects can last beyond an hour and a half of drinking the tea.
Understand the problem with iron. Know the problem with glaucoma. Avoid drinking green tea with meals if you have an iron deficiency. Avoid green tea altogether with glaucoma.