Rooibos (Aspalathus linearis) extract, containing eriodictyol-6-C-β-D-glucoside as the active component, stimulates exocrine glands via the M ₃ muscarinic acetylcholine receptor

We previously discovered that rooibos extract activates the M ₃ muscarinic acetylcholine receptor (M3R), a key component of exocrine secretion. In this study, we examined the rooibos extract for active components in vitro and monitored its fast-acting effects against dryness in humans. Our in vitro analysis demonstrated that the M3R-stimulating effect of rooibos extract was similar to that of eriodictyol-6-C-β-D-glucoside (E6CG), whereas other rooibos constituents (aspalathin, orientin, isoorientin or eriodictyol-8-C-β-D-glucoside) were not active. In a placebo-controlled, double-blinded crossover clinical trial, 36 subjects with dryness at the mouth, eyes, and skin consumed a daily dose of either 100 mg rooibos or placebo tablets for three days. Rooibos extract ingestion increased resting-saliva content, tear volume, and stratum corneum moisture content, and reduced the dryness symptoms. In conclusion, rooibos extract contains E6CG as a M3R activator and stimulates exocrine gland secretion, which relieves dryness at the mouth, eyes, and skin in humans.