RecruitingClinical trialDietary Iron RequirementsDietary Reference Intakes (DRIs) for iron are based on a relatively small number of studies in European populations. This research study will determine iron needs in a representative sample of adults living in the US using the iron isotope dilution technique. Following administration and equilibration of a stable iron isotope, participants will be followed for a 12 week study period. Blood will be collected every 4 weeks and the isotopic composition will be determined. Results will help update dietary iron guidelines making sure they better match the specific needs of the US population.