The development of a vitamin C-deficient diet using a selective menu design

Abstract

The amount of vitamin C found in human plasma as a direct function of dietary ingestion is unknown. This relationship, which must be understood to predict the ideal vitamin C requirement, can be identified by assaying serum from hospitalized normal volunteers who are placed on a controlled, vitamin C-deficient diet. With the development of a unique assay for serum ascorbic acid analysis, an 18 week study was designed, requiring the creation of a vitamin C-deficient diet. A 14-day cycle, selective menu design was used to develop a diet restricted to ≤5 milligrams (mg) vitamin C daily. This approach depleted both plasma and dietary vitamin C, while controlling for other nutrients. The three volunteers who have completed this study to date depleted plasma vitamin C from >50 micromolar (umol/L) to 7.0 ± 1.0 umol/L (scorbutic range) within 1–3 weeks. The diet was maintained and daily intake was monitored throughout the repletion phase of the study, during which time controlled oral and intravenous vitamin C doses were administered. Plasma ascorbic acid increased from 7.0 ± 1.0 umol/L to 76 ± 18 umol/L with subsequently increased doses of vitamin C. Nutritional parameters remained within normal ranges. Mean dietary compliance, calculated by number of days with <5.0 mg vitamin C/total days on study, was 84.5 ± 8.7% over the 18 weeks. This rate is indicative of the high degree of diet acceptance achieved with a selective menu design. This successfully developed diet was essential to the study of ascorbic acid pharmacokinetics over a 4–5 month period.