Evidence Level
Turkey tail has the deepest evidence base of any medicinal mushroom. PSK (polysaccharide-K) has been approved as an adjunctive cancer therapy in Japan since 1977, and a 2012 meta-analysis by Oba et al. analyzing 8,009 patients across 13 RCTs found that PSK significantly improved overall survival in gastric and colorectal cancer patients receiving chemotherapy. In the United States, a Phase I clinical trial funded by the NIH (Torkelson et al., 2012) found that turkey tail significantly increased NK cell activity in breast cancer patients after radiation therapy, with dose-dependent immune enhancement at 3, 6, and 9g/day. For general immune support, Pallav et al. (2014) demonstrated that turkey tail supplementation modulated gut microbiome composition in healthy volunteers, increasing beneficial Bifidobacterium and Lactobacillus strains. The beta-glucan content of turkey tail activates the complement system and enhances macrophage phagocytosis through dectin-1 and CR3 receptor binding.