Tea and Iron

Monday, Oct 22, 2007

This is an article I’ve been meaning to write for a long time. The effect of tea on iron absorption is something I get asked about a lot, and something that is surrounded by loads of misinformation. So, let’s start setting the record straight . . .

Let’s begin with tannins. Tannins are naturally occurring molecules in tea and (as you may have noticed) they have a bad reputation because of their association with tannic acid (which is used to tan hides to make leather). Though the tannins in tea are in the same class of chemicals as tannic acid, tea does NOT (contrary to popular belief) contain ANY tannic acid. The tannins tea DOES contain are catechins (like EGCG, which is reported to aid in weight loss) and other bioflavonoids (molecules that are noted for their antioxidant properties). Some of these tannins are responsible for the dark color and astringent taste in some teas, particularly black and Oolong teas. Many of them are found in other “healthy” foods, such as berries, pomegranates, and wine.

So tannins are good, right? Yes and maybe also no. It all comes down to iron. You see, dietary iron comes in two forms: heme and non-heme. Heme iron is from meat sources and non-heme iron is from plant sources, such as cereal grains, legumes, and leafy greens. Heme iron is generally unaffected by tannins and is typically absorbed at a rate of 10-30%, depending on the body’s level of need for it at the time. Non-heme iron, on the other hand, IS affected by the tannins in tea and is only absorbed at a rate of only 2-10%. So, if you eat meat and are not diagnosed as anemic, then you will have no problems drinking as much tea as you like before, after, and during meals. However, if you are vegetarian/vegan and/or are diagnosed anemic, then you may want to place some restrictions on your tea drinking. Here’s why:

Tannins chelate non-heme iron. This means that they form an insoluble bond with some of the iron molecules, making it undigestible. The degree of chelation is dose-dependant: the more tea you drink during a meal, the less iron is absorbed. (FYI, calcium also chelates iron, particularly when taken in a large dose as a supplement, and foods such as spinach and soy are thought to chelate iron at a similar rate to tea.) The typical decrease in iron absorption from a meal with a cup (as in measuring cup) of tea in clinical studies is approximately 30-60%. If you’re already low on iron it can make a big difference. This reduction in absorption can be minimized in several ways.*

The most commonly suggested means of managing non-heme iron and tea are to drink less tea and to not drink tea with meals. Three to four cups of tea a day is perfectly fine for a healthy vegetarian/vegan or for someone with mild anemia, provided you don’t drink it all during your one iron-rich meal of the day. Drinking tea no less than an hour before and after your meals greatly reduces the inhibition of iron absorption.

(I know what you’re thinking. “You want me to drink LESS tea and plan my meals around my tea-drinking! You must be crazy!” You didn’t think I’d go on all this time just to say that, though, did you? No, no, it gets better. Read on.)

Vitamin C and some other acids (such as lactic acid in milk and malic acid in pumpkins and plums) aid in non-heme iron absorption and can help to counteract the interference with absorption caused by tannins by adding an electron and changing it from its ferric form (which is harder to digest) to its ferrous form (which is easier to digest). Some studies have shown a threefold increase in non-heme iron absorption due to an increase in vitamin C intake during a meal. Simply put, a little lemon in your tea goes a long way.

Calcium can also act as a friend rather than a foe in iron absorption. By adding a splash of milk to your tea (typically a faux pas, but quite nice with some Assam and Ceylon teas), you can cause the tannins to bind with calcium BEFORE either one can bind with your iron. Clever . . .

Another solution is to switch to tisanes (“herbal teas”), which tend to be much lower in tannins and often taste good with a bit of lemon juice.

If you (like me) prefer “true teas” (white, yellow, green, oolong, black, and pu-erh, all from the Camellia Sinensis plant), then you may consider moving to the “lighter” teas on the spectrum (white, yellow, and green) to try to reduce the amount of tannins per cup. Separate studies have stated that green tea reduces iron uptake by about 30% and black tea reduces iron uptake by about 60%, though no major comparative studies in iron absorption have been performed to date.

A tasty solution is to avoid oversteeping your tea, as oversteeping releases excess tannin (hence the bitter taste of overbrewed tea).

The final way to increase non-heme iron absorption is very obvious, but often overlooked in this kind of conversation. EAT MORE IRON. Lots of foods are rich in non-heme iron. Cereals, dried beans, nuts, leafy greens, tofu, potatoes, raisins, broccoli and all kinds of other yummy foods are good sources of it. Just swap out the iceberg for Swiss chard and the sugar for blackstrap molasses and you’re on your way!

So, now you know how tannins and iron interact and how to reduce the impact tannins have on the absorption of non-heme iron. However, I feel it would be utterly wrong of me to finish this article without including one more little gem on tea and iron. One of tea’s BENEFITS may be its interference with iron absorption. Crazy talk? Maybe not.

When you have an infection, your immune system produces chemicals (like Lcn2) and cells (macrophages) that withhold iron from bacteria, making it impossible for them to reproduce. Thus, drinking more tea when you have an infection may help you to heal sooner. (However, this is not something that has been adequately tested/proven, so please don’t go around stating it as fact!)

Additionally, tea’s reduction of iron absorption may be of use to people with hemochromatosis, a disease that causes the body to stockpile iron and (in later stages) encourage cancerous growth (due to the overabundance of iron). Little is known about hemochromatosis at present (most doctors don’t even know how to properly diagnose it at this point), but this study shows promise in the use of high-tannin tea to reduce the storage of iron in the system (by about 30%) and, thus, reducing the necessity/frequency of drawing blood as a means of treatment. The way I figure, if advanced bloodletting is the main form of treatment for hemachromatosis, then drinking some extra tea really can’t hurt.

*Please note that I am NOT a medical doctor, I am just someone who knows a lot about tea. If you have an iron deficiency or excess, talk with your doctor or dietician about what is best for you.