DEAR DR. BLONZ: I’m a 69-year-old male, vegan, with an active cycling routine. For most of my adult life, I’ve been a blood donor without any problems. About two years ago, I began consistently failing the initial screen due to low blood iron. Eventually, one of the technicians asked if I drank tea. I had, in fact, begun drinking tea daily around the time I began failing the blood screen. A few weeks ago, after abstaining from tea for a few days, I passed the screen and successfully donated.
My online research seems inconclusive about whether tea depletes iron. I would have thought that low blood iron would seriously affect my cycling performance, but I haven’t seen definite signs of that. To what extent does tea deplete blood iron? Will drinking a cup or two of tea per day affect endurance and athletic performance? -- S.H., Tulsa, Oklahoma
DEAR S.H.: My compliments to you, and all who are blood donors; it is a generous pay-it-forward way to give of ourselves, and help others in a way unlike any other.
Donation centers don’t typically measure blood iron directly; what they screen for is the level of hemoglobin, the iron-containing “metalloprotein” in red blood cells designed to carry oxygen. Blood accounts for about 10% of body weight, about 1.2 to 1.5 gallons, and the amount removed during the donation should only have a minimal, short-term impact on the oxygen-carrying ability of a donor’s blood. We have extra blood stored in the spleen, so the blood volume is rapidly replenished. For more on donations, see b.link/donor.
Kudos also on your healthful approach, and to your detective work in having tea on the suspect list. Teas made from black tea leaves, and to a lesser extent, oolong, then green, contain tannins that can bind with minerals such as iron and affect their absorption. This is not tea depleting body iron; it is the tannins affecting absorption, so dietary iron is less able to make it in. (I realize this might seem odd, but for physiological reasons, the digestive tract is often considered to be outside of the body; it’s only after a substance is absorbed that it is considered “in.”) Think of the tannin effect as a physical phenomenon within your digestive system, where the tannins are binding with the mineral to form a compound that is too large to be absorbed.
Your experience with a brief cessation of tea drinking and with your cycling would suggest that this may only be a minor issue. You could counter the effect by avoiding drinking high-tannin teas with iron-rich meals. (There is a list of vegetarian sources of iron at b.link/zr38h.)
I do recommend you relate these experiences to your health professional to help decide if a more informative blood test would be indicated.
Finally, tea has several healthful benefits, so enjoy. There are teas with low, or no tannins, and certain herbal teas are tannin-free.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.