Abstract

Background
Studies of cold-dwelling humans show lower bone mineral density (BMD) and greater age-related bone loss. While cold exposure is regularly used for analgesic purposes, prolonged use may unintentionally exacerbate symptoms it aims to treat.

Objective
To evaluate human evidence on the effects of cold exposure upon markers of bone health.

Methods
This scoping review followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. OVID (MEDLINE, EMBASE), Elsevier (ScienceDirect, Scopus), and PubMED databases were searched using the terms (“Cold temperature” OR “cryotherapy” OR “Hydrotherapy” OR “Cold stress”) AND (“Bone Matrix” OR “Bone mineral density” OR “bone formation” OR “bone remodelling” OR Osteogenesis). Inclusion criteria were: (1) cold exposure or application in humans; (2) measurement of bone health or turnover markers; and (3) original research or case reports.

Results
Searches resulted in 2,372 articles, yielding a final pool of 13 articles for inclusion after screening. Several cooling methods were used, predominantly cold air (n=6), cooling vests (n=4), sleeping in cold rooms (n=1), β3 agonist coupled with cooling pads (n=1) and ice water swimming (n=3). Markers of bone health were assessed, with BMD shown to increase following cryotherapy, and having a positive correlation with brown adipose tissue. Papers returned suggest a neutral or positive response in factors that enhance osteoblast differentiation (irisin, insulin-like growth factor-1 [IGF-1], meteorin-like protein [METRNL]), which fails to translate directly into improved bone formation (procollagen 1 N-terminal propeptide [P1NP], osteocalcin).

Conclusion
Cold exposure might dampen bone resorption mechanisms (beta isomerised C terminal telopeptide of type 1 collagen [β-CTX]) but not others (receptor activator of nuclear factor κ B [RANK], RANK ligand [RANKL], interleukin-6 [IL-6]). Hormonal markers of bone remodelling (thyroid stimulating hormone [TSH], parathyroid hormone [PTH], triiodothyronine [T3]) also showed contrasting effects. As such, the limited data does not allow for clear conclusions.