Fig. 3.

Effect of gut microbiota and metabolites on bone metabolism. The gut ecosystem can affect bone homeostasis via (a) modulating gut barrier integrity; (b) enhancing the absorption of Ca²⁺ and Mg²⁺; (c) regulating the inflammatory response by balancing Th17 and Treg cells differentiation; and (e) directly promoting the activation of osteoblasts while suppressing the differentiation of preosteoclasts. Blue line: Stimulation or activation. Red line: Suppression or infibition. IGF-1, Insulin-like growth factor-1. LPS, Lipopolysaccharide. PTH, Parathyroid hormone. SCFAs, Short-chain fatty acids. Th, T helper. Treg, T-regulatory.