beta-carotene does not change markers of enzymatic and nonenzymatic antioxidant activity in human blood

In vitamin A-replete populations, increased concentrations of serum caroten oids have been associated with a decreased risk of degenerative diseases. T he mechanism of action of carotenoids in determining antioxidant activity i s largely unknown. The aim of the study was to examine the effect of carote noid supplementation and spinach intake on erythrocyte enzyme antioxidant a ctivities, serum or plasma nonenzymatic antioxidant concentrations, and con centrations of oxidatively damaged amino acids in plasma; Subjects received for 3 wk a basic diet (n = 10), a basic diet with a carotenoid supplement (n = 12) or with a spinach product (n = 12 per group), i.e., whole-leaf, mi nced, liquefied or liquefied spinach plus added dietary fiber. After 3 wk o f dietary intervention, changes in serum or plasma concentrations of ascorb ic acid, alpha-tocopherol, FRAP (ferric reducing ability of plasma) and uri c acid and erythrocyte enzyme activities were assessed, and differences amo ng experimental groups were tested. Consumption of spinach resulted in grea ter (P < 0.01) erythrocyte glutathione reductase activity and lower (P < 0. 05) erythrocyte catalase activity and serum alpha-tocopherol concentration compared with the control group. Consumption of the carotenoid supplement l ed to lower alpha-tocopherol responses (P = 0.02) compared with the basic d iet only. Our data suggest that the short-term changes in erythrocyte gluta thione reductase activity and serum alpha-tocopherol concentration can be a ttributed to an increased carotenoid (lutein and zeaxanthin) intake, but be ta-carotene is unlikely to be a causative factor. Lower erythrocyte catalas e activity after intervention with spinach products may be related to other constituents in spinach such as flavonoids.