Stem cells maintain tissue homeostasis and repair. Embryonic stem cells are pluripotent; adult stem cells are tissue-specific (hematopoietic, mesenchymal, satellite cells for muscle, etc.).
Mechanism — Self-renew through asymmetric division, generating one new stem cell and one specialized cell. Stem cell pools and function decline with age — fewer cells, less responsive, and a more inflammatory niche.
Use case — Support endogenous stem cell function: adequate sleep, exercise (especially for satellite cells in muscle), nutrient-dense diet, fasting (transient HSC mobilization). Mesenchymal stem cell therapy is real but still investigational for most indications.
Caveats — Stem cell clinics are a regulatory minefield in the US. Most marketed treatments lack rigorous evidence. Choose clinics with proper sourcing, characterized cells, and tracked outcomes — the variability is enormous.