Do iron and vitamin C co-supplementation influence platelet function or LDL oxidizability in healthy volunteers?

Abstract

Objective: To examine the effect of co-supplementation with iron and vitamin C on antioxidant status, platelet function and low density lipoprotein oxidation in normal healthy volunteers.

Design: The study was carried out with two groups of 20 subjects each acting as their own control, comparing presupplemention with postsupplemention. One group was supplemented with iron and the RDA level of vitamin C and the second group with iron and 260 mg/d vitamin C.

Setting: The International Antioxidant Research Centre, The Guy’s, King’s College and St Thomas’s School of Biomedical Science, Guy’s Campus, London.

Subjects: Forty normal healthy volunteers, recruited from the staff of the Medical School and Hospital in which two volunteers withdrew during the study.

Interventions: Subjects in both studies were randomly assigned to one of two groups (5 males and 5 females group) and received supplements containing iron (14 mg/d) and either 60 mg/d (Group A) or 260 mg/d (Group B) vitamin C for 12 wk. Blood samples were taken at 6 wk and 12 wk, and prior to supplementation and analysed for iron and antioxidant status (transferrin bound iron, vitamin C and E, and β-carotene levels) in both studies. Samples from the first study were analysed for the susceptibility of LDL isolated from plasma to Cu²⁺-induced oxidation and samples from the second for platelet function.

Results: Transferrin-bound iron was significantly increased (P<0.05) at 12 wk, in Group A subjects (from 14.9±5.3 μmol/l to 19.5±2.3 μmol/l; mean±s.d.; n=19), whereas those in Group B showed a significant increase (P<0.05) after 6 wk (from 15.8±4.5 μmol/l to 20.4±6.6 μmol/l; n=19) which decreased at 12 wk (16.3±5.0 μmol/l). Plasma total ascorbate significantly increased from an initial level of 59.3±21.3 μmol/l to 87.6±29.0 μmol/l after 6 wk and 81.7±11.4 μmol/l after 12 wk following the Group B supplementation, but only after 12 wk in Group A (from 64.0±24.8 μmol/l to 77.2±13.2 μmol/l). Plasma α-tocopherol concentrations were significantly increased after 6 wk and 12 wk with both levels of supplementation (from 24.2±5.7 μmol/l Group A and 23.4±5.3 μmol/l Group B to 26.3±5.5 μmol/l and 25.7±4.7 μmol/l respectively at 12 wk). The mean lag phase to oxidation of low density lipoprotein (LDL) was significantly increased in subjects in Group B after 12 wk ingestion of iron and 260 mg vitamin C (from 80.0±14.8 min to 97.2±16.9 min; n=9). Platelet sensitivity to ADP-induced aggregation was significantly decreased (P<0.05) by 12 wk in Group A (from EC₅₀ 2.3±1.3 μM to 3.7±2.2 μM; n=10), whereas those receiving higher vitamin C showed a significant decrease (P<0.05; from EC₅₀ 1.9±0.6 μM to 3.1±1.8 μM) after 6 wk which subsequently increased towards presupplemental levels (2.6±1.6 μM). Platelets from the latter subjects showed a significant reduction in ADP-induced ATP secretion at both 6 wk and 12 wk.

Conclusion: The results show modest beneficial effects on LDL oxidation and platelet function following supplementation with iron and vitamin C. No evidence for pro-oxidant effects was observed.

Sponsorship: This work was funded by the Ministry of Agriculture, Fisheries and Food (AN 0513).