The body begins to upregulate iron absorption at a ferritin concentration of less than 50 µg/L, indicating an incipient iron deficiency in young women.

2021 EClinicalMedicine Threshold ferritin and hepcidin concentrations indicating early iron deficiency in young women based on upregulation of iron absorption Galetti V, Stoffel NU, Sieber C, Zeder C, Moretti D, Zimmermann MB

Cohort Study Ferritin Hepcidin Iron Absorption

In the methodology, this study utilizes a pooled analysis of stable iron isotope studies conducted between 2006 and 2019 on healthy women aged 18 to 50. These studies quantified iron absorption from meals providing physiological quantities of iron. A mathematical model known as generalized additive modeling was employed to ascertain the relationships between iron absorption, ferritin, and a molecule called hepcidin. By estimating the first derivatives of the trend created by the model, inflection points (or thresholds) in these relationships were established.

The results revealed that hepcidin increased in a linear fashion parallel to ferritin. Iron absorption increased when hepcidin reached a threshold value and when a threshold ferritin value was detected, beyond which iron absorption remained stable. An auxiliary validation within the results found that a hepcidin of approximately 3 nmol/l corresponded to a ferritin level of approximately 51 µg/l. These findings collectively suggest that if the body's ferritin concentration falls below 50 µg/L—corresponding to a hepcidin level of less than 3 nmol/l—the body will respond by absorbing more iron from the diet, signaling an emerging iron deficiency.

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