Balneotherapy and cortisol levels: an updated systematic review and meta-analysis

The main objective of this review is to examine the impact of balneotherapy on serum and salivary cortisol concentrations. A systematic search was conducted in PubMed, Scopus, Web of Science, PEDro, and Google Scholar. The databases were screened from inception up until April 2024. After screening the scientific literature, 845 articles were retrieved and 17 studies, involving a total of 765 participants, were eventually included in the review. Among them, four were randomized controlled trials, five were non-randomized studies, and eight were pre-post studies with no control group. The evidence gathered in this review indicates a significant short-term reduction in cortisol levels in healthy individuals undergoing balneotherapy, particularly those experiencing high levels of stress. Conversely, in patients with rheumatic conditions (especially if elderly), increases in cortisol levels induced by balneotherapy can act as beneficial hormetic stress, reducing inflammatory mediators and improving pain and functional quality of life. The meta-analysis shows an overall trend of reduction in stress hormone levels, more pronounced in the intervention group undergoing mud-balneotherapy compared to the control group, a finding that, however, does not reach statistical significance (g=-0.11 [95% CI: -0.30; 0.08]; p > 0.05). Current scientific evidence demonstrates that balneotherapy has a positive impact on the regulation of cortisol levels. The regulation of the hypothalamic–pituitary–adrenal axis and the beneficial effects observed on health parameters and quality of life allow mud-balneotherapy to be classified as eustressful stimuli useful in preventing stress-related pathologies in healthy individuals and in alleviating symptoms in patients with chronic conditions. Future research on the topic is advised.