Rooibos was shown to enhance the activity of glutathione-S transferase and UDP-glucuronosyl transferase in rat liver (11) (16), allowing cells to protect against oxidative stress, and to reduce the effects of hepatocarcinogens. A study of oxidative stress in rats found that serum superoxide dismutase and urine 8-hydroxy-2'-deoxyguanosine (8-OHdG) concentrations (as markers for DNA damage) were significantly reduced following administration of rooibos (17). Some studies have shown that the non-oxidized teas have greater antimutagenic effects compared to the oxidized forms. This is probably due to reduction in total polyphenol content with oxidization (11) (18) (19). The anti-inflammatory effects of rooibos are thought to be due to its inhibition of COX-2 enzyme (5).
Rooibos also modulates immune function: It induces higher IL6, IL10 and IFN-gamma levels and increases cell-mediated immunity (3); and increases IL2 levels while suppressing IL4 (4).
In other studies, rooibos significantly decreased glucocorticoid levels in rats and steroid metabolite ratios linked to metabolic disorders-cortisol:cortisone in humans and CORT:testosterone in rats (23).
Hot water-soluble solids from fermented rooibos inhibited adipogenesis and influenced adipocyte metabolism, suggesting a role in preventing obesity (24).