β-Carotene Supplementation Increases Antioxidant Capacity of Plasma in Older Women , ,

Abstract

The antioxidant effect of dietary β-carotene supplementation on the peroxidation potential of plasma was investigated in a randomized double-blind, placebo-controlled study. Twelve healthy women (62–80 y) supplemented their usual daily diet with 90 mg of β-carotene (n = 6) or placebo (n = 6) capsules for 3 wk. Plasma concentrations of β-carotene, α- and γ-tocopherol, ascorbate, urate, bilirubin and in vitro production of phosphatidylcholine hydroperoxides (PC-OOH) and utilization of plasma antioxidants in the presence of 50 mmol/L 2,2′-azobis (2-aminopropane) hydrochloride (AAPH), a free radical generator, at 37°C were measured before and after dietary treatment. Plasma β-carotene increased from 0.76 ± 0.16 to 6.45 ± 1.16 µmol/L (P < 0.05) in supplemented but not placebo-treated subjects. The plasma concentrations of other antioxidants did not change significantly in either group. β-Carotene supplementation did not affect basal levels of plasma PC-OOH as measured by HPLC post-column chemiluminescence but did affect AAPH-induced production of PC-OOH. Before supplementation, the induction period of plasma PC-OOH production was 2.4 ± 0.4 h, with levels reaching 5.39 ± 1.50 µmol/L after 6 h of incubation. After supplementation, the induction period increased significantly to 4.2 ± 0.4 h (P < 0.01), with a lower PC-OOH production of 2.16 ± 0.90 µmol/L after 6 h (P < 0.05). In this system, plasma ascorbate concentrations were depleted first, followed by loss of bilirubin and α-tocopherol and then by the sequential loss of γ-tocopherol, urate and β-carotene. These results indicate that β-carotene supplementation increases the plasma antioxidant capacity of older women.