The serum or plasma ferritin concentration (referred to hereafter as ferritin) is the most widely used indicator to detect iron deficiency and a low ferritin indicates depleted iron stores. However, the threshold ferritin that defines iron deficiency remains unclear and diagnostic ferritin cutoffs from expert groups vary widely.

Our study aim is to define the ferritin in Kenyan young women at which the body senses iron depletion and begins to upregulate iron absorption from the diet; this approach could provide a functionally defined threshold of iron deficiency in Sub-Saharan African women.

Inclusion Criteria:

• Age 18-28 y, not pregnant or lactating
• Body weight <75 kg
• body mass index (BMI) between 17 and 25 kg/m2
• No acute illness/infection (self-reported)
• No metabolic or gastrointestinal disorders (self-reported)
• No use of medications affecting iron absorption or metabolism during the study
• No intake of mineral/vitamin supplements 2 weeks prior to the first study visit and during the study