Effects of balneotherapy on stress, anxiety, and depression: results of a multicenter randomized controlled trial with six-month follow-up

Balneotherapy (BT), involving the use of natural resources such as mineral water, peloids, and climate exposure, is increasingly recognized as a complementary intervention for stress-related mental health conditions. This study aimed to evaluate the short- and long-term effects of a standardized BT complex on stress, anxiety, depression, and related outcomes. A multicenter, randomized, controlled, single-blinded (researchers) parallel-group trial was conducted in six Lithuanian medical spa centers. Adults aged 18–65 years with moderate to high stress levels (N = 243) were randomized into three intervention groups—ambulatory BT (11ABT), ambulatory BT plus nature therapy (11ABTNT), inpatient BT (11BTS)—and one control group (11 C). The treatment period was 11 days, with assessments at baseline, post-intervention, 3 months, and 6 months. Primary outcomes included perceived stress (PSS-10), salivary cortisol, anxiety (STAI-5), and depression (CESD-R). Secondary outcomes were fatigue (FAS), sleep quality (SQS), functional adaptation (WSAS), integrative well-being, cognitive performance, and treatment safety. All intervention groups showed statistically significant improvements across primary and secondary outcomes compared to baseline (p < 0.001), with medium to very large effect sizes. The greatest short-term effects were observed in the inpatient group (11BTS), including reductions of 46% in stress intensity, 54% in depression, and 49% in sleep impairment. Improvements in fatigue, anxiety, and stress management were also notable. These effects persisted at 6 months, with sustained reductions of up to 31% in stress, 27% in anxiety, and 50% in stress management. Sleep quality improved by up to 67%, and integrative outcomes by 40%. No serious adverse events were reported, and treatment was well-tolerated across all sites. Balneotherapy using natural resources is a safe, effective, and sustainable complementary approach for improving mental health. The observed reductions in stress, anxiety, depression, and fatigue—alongside enhanced sleep and functioning—suggest that BT may be a valuable addition to integrative care strategies for stress-related conditions. Further large-scale trials are warranted to confirm these findings and support wider clinical implementation. ClinicalTrials.gov Identifier NCT06018649 (August 25th, 2023).