Potential health benefits of cold-water immersion: the central role of PGC-1α.

Cold-water immersion (CWI) elicits a coordinated thermoregulatory and stress-response programme that may converge on molecular pathways linked to peroxisome proliferator-activated receptor-γ co-activator-1α (PGC-1α), a master regulator of mitochondrial biogenesis and a coordinator of angiogenesis, antioxidant defence and metabolism. Through activation of peripheral cold receptors (e.g. TRPM8), CWI triggers sympathetic noradrenaline release and hypothalamic-pituitary-thyroid axis stimulation (TSH→D2→T3), driving β-adrenergic/cAMP-PKA-p38MAPK-CREB signalling that could robustly upregulate PGC-1α and uncoupling protein-1 in brown adipose tissue and skeletal muscle. Concurrent shivering-induced Ca2+ fluxes engage calcium/calmodulin-stimulated protein kinase II and calcineurin, enhancing PGC-1α expression in an AMP-activated protein kinase (AMPK)-independent manner. Elevated PGC-1α coactivates nuclear respiratory factors (NRF1/NRF2) and mitochondrial transcription factor A to expand mitochondrial content and oxidative capacity, while upregulating key antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase). Together with oestrogen-related receptor α, PGC-1α can co-activate vascular endothelial growth factor, a pathway compatible with angiogenesis and improved perfusion; however, in humans the link to CWI remains indirect and is largely limited to acute molecular responses. Downstream metabolic adaptations, including increased fatty acid oxidation (via carnitine palmitoyltransferase 1, peroxisome proliferator-activated receptors α/γ and AMPK) and fibroblast growth factor 21 secretion, enhance insulin sensitivity and energy expenditure. Most of the evidence currently rests on molecular signalling data, heterogeneous study designs, or acute gene expression responses. Direct evidence for increased mitochondrial content, improved mitochondrial function, or long-term health benefits in humans is scarce. Therefore, this article introduces a hypothetical dose-response relationship, linking immersion time to proposed health benefits and death, and provides practical recommendations for safe CWI protocols.