When is iron most bioavailable?

Iron is an essential nutrient for human health. A lack of it can lead to low energy, heart palpitations and shortness of breath, and even anaemia. Iron deficiency can also have long-term affects on the growth of children.

For a human to take in enough iron in the food they eat, it must be bioavailable to allow for its absorption.

What is bioavailability?

Bioavailability is, essentially, how much of a given nutrient is absorbed into the body after it is consumed as part of a food.

“It describes the capability of a micronutrient source to contribute to the physiological requirements for that micronutrient,” Susan Fairweather-Tait, professor of human nutrition at the University of East Anglia, says.

The bioavailability of iron in particular, she told us, is measurable. “For iron, it is possible to directly measure utilisation (i.e. bioavailability) as the percentage incorporation of an isotopically-labelled dose of iron into haemoglobin (whereby 80% of absorbed iron is incorporated into haemoglobin).”

What affects the bioavailability of iron?

The bioavailability of iron in food varies highly. According to Jeannine Baumgartner, lecturer in nutritional science at King’s College London, it often depends on both the type of iron and whether or not iron absorption inhibitors or enhancers are present in the food or meal matric.

Haem iron, which is found in animal-based foods, is significantly more bioavailable than non-haem iron found in plant-based foods. Absorption studies, she told us, indicate that while the bioavailability of non-haem iron is 2-20%, the bioavailability of haem iron is 15-40%.