Formulation of Vitamin A Tracer Doses for Administration to Human Subjects using Retinol Isotope Dilution Technique

The retinol isotope dilution (RID) technique relies on the administration of isotopically labeled vitamin A tracers to human subjects. Here, we present a method to guide research teams on how to prepare vitamin A stable isotope tracers for both research studies and population surveys. The article provides an overview of the preparation, sourcing of materials, equipment required, and procedures to ensure that the tracers are safe for human consumption. Vitamin A stable isotope tracers can be obtained commercially and are usually labeled with either deuterium [²H] or carbon-13 [¹³C] with >95% all-trans isomeric purity and >99% isotopic enrichment. The preparation of the vitamin A stable isotope tracers involves dissolving the tracer in edible vegetable oil through sonication and heat. Tracers need to be prepared at a concentration that is well within the volumetric limits of the delivery system. Finally, the tracer is aliquoted into sterile amber glass vials, and tracer concentrations are confirmed spectrophotometrically.