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Effect of transferrin polymorphism on the metabolism of vitamin C in Zimbabwean adults^1,2,3

¹ From the Departments of Chemical Pathology (IK and ZARG) and Medicine (ITG, HK, VMM, TS, and EM), Medical School, University of Zimbabwe, Harare, Zimbabwe; the Department of Clinical Chemistry, University of Ghent, Ghent, Belgium (JRD and MRL); the Unit of Renal and Infectious Diseases, AZ St Jan, Bruges, Belgium (JRB); and the Department of Medicine, Howard University, Washington, DC (VRG).

Background: Transferrin is the major iron binding protein in human plasma. In black persons, the transferrin CD phenotype has been associated with alterations in certain markers of iron status.

Objective: We studied vitamin C status in a Zimbabwean population according to transferrin phenotype because vitamin C metabolism is influenced by iron-driven oxidative stress.

Design: The study population consisted of 150 black African adults, 90 of whom were at risk of iron overload on the basis of high dietary iron content in the form of traditional beer. Transferrin phenotypes, indirect measures of iron status, and leukocyte ascorbic acid concentrations were determined. The in vitro rate of L-ascorbic acid depletion in sera from different transferrin phenotypes was investigated.

Results: The transferrin phenotype frequencies of transferrin CC and CD were 0.893 and 0.107, respectively. The iron status of transferrin CC and CD subjects was similar. After adjustment for traditional beer consumption, baseline leukocyte vitamin C concentrations were significantly higher in 16 transferrin CD subjects ( ± SE: 2.10 ± 0.34 and 2.61 ± 0.28 fmol/leukocyte in men and women, respectively) than in 134 transferrin CC subjects ( ± SE: 1.65 ± 0.11 and 1.99 ± 0.11 fmol/leukocyte in men and women, respectively; P = 0.024). Oral administration of ascorbic acid (2.0 g every 24 h for 48 h) led to slower rises in leukocyte vitamin C concentrations in subjects with the transferrin CD phenotype than in subjects with the transferrin CC phenotype (P = 0.028). After in vitro supplementation of serum with 570 µmol vitamin C/L, the rate of L-ascorbic acid depletion was significantly lower in subjects of a transferrin CD phenotype than in subjects with the transferrin CC phenotype.

Conclusion: Transferrin polymorphism may affect vitamin C status in blacks.

Key Words: Africa • transferrin • phenotype • vitamin C • L-ascorbic acid • iron status • scurvy • blacks