Alternate Day vs. Daily Iron Supplementation in Iron Depleted Women

Inclusion Criteria: * Female, 18 to 45 years old, * SF levels \<25 μg/L, * Hb levels ≥ 11 g/dL * Normal Body Mass Index (18.5-25 kg/m2), * In possession of a mobile phone on which the study app can be loaded, * Signed informed consent, * Not mandatory (only for subgroup analysis): having participated in a former stable iron isotope study in our laboratory between 1-5 y ago Exclusion Criteria: * Elevated CRP \> 5 mg/L, * Any metabolic, gastrointestinal, kidney or chronic disease (self-reported) affecting iron metabolism, * Continuous/long-term use of medication, which may interfere with iron absorption, gut physiology and iron metabolism, * Consumption of additional iron supplements over the study period, * Consumption of iron supplements since screening, * Difficulties with blood sampling, * Known hypersensitivity or allergy to iron or placebo capsules in the given amount (ferrous sulfate, mannitol, silica) * Pregnancy, breastfeeding * Women who intend to become pregnant during the course of the study, * Known or suspected non-compliance, drug or alcohol (more than 2 drinks/day) abuse, * Smokers (\> 1 cigarette per week), * Participant is likely to be absent on one the study appointments, * Inability to follow the procedures of the study, e.g. due to language problems, self-reported psychological disorders, etc. of the participant.