By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily
Iron plays an integral role in brain development and the functioning of our immune system. However, several factors can influence the bioavailability of iron, or our body’s ability to absorb this mineral.
Tannins and Iron Bioavailability
Tannic acid, sometimes known as “tannins,” is found in coffee and tea and is responsible for a bitter taste. Tannins cause a decrease in iron absorption so much so that if you drink coffee or tea around an hour before or after a meal, particularly when it contains non-heme iron, you can reduce your iron bioavailability by as much as 40%.
Thus, if you’re taking a multivitamin with iron, you should space it out from when you’re having coffee or tea. This applies to both regular and decaf drinks, because it’s not the caffeine but rather the tannins in coffee and tea that affects iron bioavailability.
Additionally, phytates, which are found in fiber; oxalates, which are found in plants (particularly beet greens, rhubarb, and spinach); and even soy may interfere with iron absorption.
One source of dietary iron you may not be aware of is steamed clams. Approximately, a 3.5-ounce portion contains 22 milligrams (mg) of iron. Additionally, cooked oysters contain about 8.5 mg of iron in the same portion size—about 3.5 ounces.
You may be wondering how much iron you need. The daily reference intakes for iron are based on age, gender, and stage of life cycle.
Males between the ages of 19 and 70 require 8 mg. Females between the ages of 14 and 18 require 15 mg. Females ages 19 to 50 require about 18 mg. At the end of menstruation and the beginning of menopause, women ages 51 to 70 require only 8 mg; so the amount becomes close to the requirement for males.
On average, the typical American diet contains about 10 mg of iron per every 1,000 calories consumed; but, this is the typical American diet that’s going to contain heme iron or animal-based iron.
Children, pregnant or menstruating women, and repeat blood donors are at the most risk for iron deficiency. One in 10 premenopausal women in the United States has an iron deficiency.
“In Houston, one of the challenges that we’ve had is, how do we manage this level of iron deficiency?” Professor Anding said. “We had a project going on at one of the local schools, in inner-city Houston, that was being remodeled. What happened was we were seeing a very huge prevalence of children in that school being iron deficient.”
As it turned out, these children actually had lead poisoning. The school was being remodeled, and the administrators were refinishing the surfaces.
The leaded paint became airborne, competing with iron for absorption. All of these children undergoing standardized tests in school had an iron deficiency, which decreased their cognition and their ability to perform on the standardized tests. Thus, this example shows how non-dietary interference can occur with iron absorption.
Another instance where you can see iron deficiency is in the use of non-steroidal anti-inflammatory drugs. In fact, these medications actually erode the lining of the stomach and cause stomach bleeding. You usually won’t experience pain or see blood in your stool, but you can still end up overtly iron deficient.
Overall, then, the number one reason that Professor Anding sees in her clinical practice for anemia among men is from non-steroidal anti-inflammatory drug use, including pain medications that impact iron bioavailability. Tomorrow’s article will delve more deeply into iron deficiency and associated symptoms.
Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.