Dietary 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.

Inclusion Criteria:

• Males and premenopausal females age 18-50 y
• Previously participated in an iron stable isotope study or willing to consume an oral stable iron isotope and undergo a one-year equilibration period
• Willing to refrain from iron-containing supplements for the duration of the study
• Willing to refrain from tobacco smoking for the duration of the study
• Have not donated blood 3 months prior to the start of the study and willing to refrain from donating blood for the duration of the study
• Willing to have blood stored for future use
• Able and willing to comply with study requirements and consent to participate

Exclusion Criteria:

• Females: pregnant or lactating or plans to become pregnant during the study period
• Inability to provide informed consent and engage in informed consent procedures
• Plans to relocate outside the study area