Black tea rich in polygonatum sibiricum polysaccharides inhibits osteoporosis in ovariectomized mice through immune regulation and gut microbiota suppression

There is a growing interest in identifying dietary strategies to prevent osteoporosis. Black tea has emerged as a potential candidate due to its demonstrated effects on bone metabolism. However, the presence of caffeine in black tea may have an adverse impact on bone health. In our study, we have formulated a compound black tea beverage (CBT) with reduced caffeine content and supplemented with food additives such as Polygonatum polysaccharide. This study aims to investigate alternative mechanisms underlying the anti-osteoporotic effects of this composite black tea preparation. Mice were randomly assigned to sham (S) group, OVX group, and CBT group. After surgery, statistical differences (P < 0.05) became evident when the thermal pain threshold was reached at 5 weeks, while the grip and mechanical pain thresholds were achieved at 6 weeks, persisting until 10 weeks. Following CBT intervention, IL-17 A, TNF-α, TGF-β, β-CTX and PINP levels displayed improvements (P < 0.05). Compared to the OVX mice, CBT mice exhibited varying degrees of improvement in BV/TV, Tb.Th, Tb.N, Tb.Sp (P < 0.05) and a significant decrease in RANKL and TNF-α protein expression in the bone tissue (P < 0.001), along with a significant increase in OPG and TGF-β1 protein expression (P < 0.001). Those treated with CBT exhibited various degrees of improvement in Th17 cells, Treg cells, and the Treg/Th17 cell ratio (P < 0.05) and displayed higher expressions of FOXP3 and lower expressions of ROR-γt in the spleen tissue (P < 0.05). CBT treatment was found to decrease the relative abundance of norank_f_Maurbaculaceae and Lactobacillus, while increasing the relative abundance of Lachnospiraceae NK4A136_group and Dubosella. CBT has been shown to functional behavioral assessments and bone microstructure, thereby effectively retarding the progression of osteoporosis. This impact is postulated to stem from certain bioactive constituents within CBT that act via immune regulation and gut microbiota modulation.