Iron absorption is the process that directly determines the risk of iron deficiency. The body cannot actively excrete excess iron, so its balance is regulated precisely at the stage of absorption in the gut.
The key 'conductors' of this process are the exporter protein ferroportin and the hormone hepcidin.
Where and how iron is absorbed
Most absorption takes place in the duodenum and the beginning of the jejunum. There are two forms: heme iron (from meat, fish, poultry) is absorbed well and depends little on other factors; non-heme iron (from plants and fortified foods) is absorbed worse (on average 5–12%) and depends heavily on the composition of the diet. To be absorbed, non-heme iron is reduced and passes through the gut cell, and then ferroportin releases it into the blood, where transferrin picks it up.
What boosts and what slows absorption
Boosting non-heme iron absorption are vitamin C (ascorbic acid) and animal protein (meat, fish). Slowing it are phytates from grains and legumes, polyphenols in tea and coffee, calcium and dairy products, and reduced stomach acidity (including on the background of antacids and proton pump inhibitors). That is why iron supplements are advised not to be taken with tea, coffee or milk.
Why absorption drops in disease
With inflammation and chronic disease, the liver ramps up hepcidin production, which blocks ferroportin — and iron stops passing from the gut into the blood. In celiac disease and Crohn's disease, the gut lining itself is damaged, so iron deficiency develops even with adequate intake.
Calculate using this marker
Calculators where Iron absorption is used directly:
Frequently asked questions
What is best to take iron with for better absorption?
With a source of vitamin C (for example, a glass of orange juice) and on an empty stomach. Avoid taking it at the same time as coffee, tea, dairy products, calcium and antacids — they reduce absorption.
Is it true that iron from plant foods is barely absorbed?
It is absorbed, but worse than from meat: non-heme iron is 5–12% bioavailable. Vitamin C noticeably increases absorption, so it is important for vegetarians to combine iron sources with vegetables and fruit.