If your doctor has prescribed you an iron supplement, you likely know that the supplement comes with certain rules. Take it with a meal if you have an easily upset stomach, for instance. Avoid consuming it with calcium, milk, or antacids, all of which inhibit your body’s absorption of iron. And there’s another rule you should add to your list: Don’t take iron with a swig of green tea or black tea.
The Case Against Black and Green Tea With Iron
Research shows that both black and green teas diminish absorption rates of iron in your body. A 2016 scientific report published in Clinical Case Reports found that green tea, when consumed in large quantities, interferes with absorption to such an extent that it can lead to iron deficiency anemia.
In addition, a 2017 study published in The American Journal of Clinical Nutrition found that black tea significantly reduced iron absorption levels. A much earlier study from 1989 found that just five milligrams of tannins can reduce iron absorption by 25 percent.
The bottom line? Black and green teas can make iron supplements ineffective.
Why do green and black tea make it difficult for your body to absorb iron?
You might think that caffeine is the main iron inhibitor in tea — and that would be a natural assumption. However, it’s only a small piece of the puzzle. A study published in Food Chemistry found that caffeine binds to a miniscule six percent of the iron in any given food. Not exactly the impact you’d expect!
The true inhibitors, it turns out, are antioxidants.
Green tea contains catechins, which are naturally occurring flavonoids, or plant compounds with powerful antioxidant properties. While catechins are beneficial because they prevent cell damage and reduce inflammation, they also interfere with the body’s ability to absorb iron.
Black tea also inhibits iron absorption in the body, but for a different reason: it contains tannins. Also known as tannic acid, tannins are polyphenols (plant compounds) with a bitter flavor and anti-inflammatory properties. When they enter the gut, they form a complex bond with iron. As a result, the body cannot easily absorb the iron into the bloodstream.
What does this mean for you?
The National Library of Medicine recommends you wait at least two hours after drinking a beverage that could interfere with your iron pill. Once two hours have passed, you can take your supplement without issue. (Or, take the supplement first and wait two hours before drinking green or black tea.)
With a little forward thinking, you should be good to go. Just be sure to double check with your doctor — a doctor will give you the best advice in terms of drinks that could interfere with your medications.