Iron Absorption: How Much Iron Are You Absorbing From Your Diet?

May 12, 2013

by Cathe Friedrich

Iron deficiency is a common problem among pre-menopausal women, especially among female athletes and women who are physically active. There’s some evidence that women who exercise heavily – long-distance running or high-intensity exercise have increased iron requirements and need more iron in their diet. Why might this be? When you pound your feet against a hard surface, it causes destruction and loss of red blood cells along with iron through the urine. You also lose small amounts of iron through sweating.

When you combine this with the fact that you lose iron monthly if you’re menstruating, it’s not hard to see why athletic women are prone to iron deficiency. That’s why it’s important to get enough iron through diet if you’re pre-menopausal and active. Just because you eat iron-rich foods doesn’t mean you’re absorbing all of the iron they contain. Here’s what you need to know about iron absorption and how to maximize your iron intake from the foods you eat.

How Much Iron Do You Absorb From Food?

You absorb more iron from animal sources like red meat. These are known as heme-based sources of iron. You absorb less from plant-based or non-heme sources of iron. When you consume animal-based iron sources, your intestines take up as much as 35% of the iron in these foods, while you only absorb 2 to 5% of the iron from plant-based foods. Not surprisingly, athletes that eat a vegetarian diet are more prone towards iron deficiency anemia and low iron stores.

Factors That Affect Absorption of Iron

Having adequate amounts of stomach acid is important for iron absorption. Low levels of stomach acid are more common than people think and levels decrease with age. If you take antacids, they reduce iron absorption by blocking stomach acid.

What you eat with iron-rich foods also impacts its absorption. Phytates are compounds in whole grain foods, nuts, seeds, beans and soy foods that block iron absorption along with the absorption of other minerals like calcium, magnesium, and zinc. Tannins in tea and oxalates in grains, nuts, chocolate and some fruits and vegetables including spinach, tomatoes, and rhubarb also reduce iron absorption from plant foods. Even though spinach is a food high in iron, it’s not the best way to meet your iron requirements because it’s in a non-heme form, and the oxalates in spinach interfere with your body’s ability to use it.

If you have low iron levels, it’s best to limit these foods and not consume iron-rich foods at the same time. If you take calcium, zinc or magnesium supplements, these can interfere with iron absorption. Iron is a 2+ ion just like calcium, zinc, and magnesium so they compete with each other for uptake by your intestines to some degree.

Are There Ways to Increase Iron Absorption From Your Diet?

Along with limiting foods that block absorption like oxalates, tannins and phytates, eating iron-rich foods along with foods high in vitamin C boosts absorption of iron from plant foods by up to three times. If you’re iron deficient, eat a source of vitamin C with your meals to increase the amount of iron your body can use.

Not Everyone Needs More Iron

If you’re an athletic, pre-menopausal female, be mindful of your iron status. Ask your doctor to check an iron panel to measure your iron stores along with your hemoglobin and hematocrit. Low iron levels, especially iron-deficiency anemia, can reduce exercise tolerance and zap your energy.

Make sure you’re getting enough dietary iron, but don’t use an iron supplement unless you’re deficient. Iron is a pro-oxidant at higher levels that can damage cells. Plus, it can accumulate in your body to toxic levels. If you’re post-menopausal, make sure your daily vitamin doesn’t contain iron. Unless your iron stores are low, you don’t need it.

The Bottom Line?

Iron deficiency is more common in active, athletic women and can reduce exercise performance. Monitor your iron status and make sure you’re getting enough dietary iron. Just as importantly, make sure you’re absorbing it properly by following these guidelines.

References:

Clin J Sport Med. 2012 Nov;22(6):495-500.

Int J Vitam Nutr Res Suppl. 1989;30:103-8.

Int J Vitam Nutr Res. 2004 Nov;74(6):403-19.

Exercise Physiology. Fifth Edition. McArdle, Katch, and Katch (2001)