Introduction

Mental disorders are leading determinants of global health. According to The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 data, depression and anxiety are the most common mental disorders that cause disability (GBD 2019 Diseases and Injuries Collaborators, 2020; GBD 2019 Fracture Collaborators, 2021). Depression and anxiety lead to decreased quality of life, increased suicide risk, and worsening physical health (Ribeiro et al., 2020; Zhang et al., 2019). Anxiety and depression have been a major concern due to their negative effects and the focus has been on their effective treatment. Treatment options such as pharmacotherapy, psychotherapy, and a combination of psychotherapy and medication are available to improve symptoms of anxiety and depression (Bandelow et al., 2017). An important limitation of psychotherapy is the insufficient number of psychotherapists and high treatment costs in low-income countries (Bernhardt et al., 2019). Psychotherapies can create stigmatization, and prejudice or increase client self-hatred (Dimidjian & Hollon, 2010). Anxiolytics and antidepressants cause physical effects such as weight gain, gastrointestinal and sexual difficulties, insomnia, severe headaches, and drowsiness, which negatively affect patient compliance with treatment (Uzbay & Yüksel, 2002). However, hydrotherapy and balneotherapy applications are very attractive because they do not require chemicals or drugs. These treatments, which have minimal side effects, have low risks for the general health and well-being of patients (Cacciapuoti et al., 2020).

Hydrotherapy aims to treat by utilizing the physical properties of water such as temperature, hydrostatic pressure, viscosity, and electrical conductivity. In hydrotherapy, plain water is used internally and externally. (Reger et al., 2022). Hydrotherapy is used to protect and improve physical and mental health. Applications such as sitting baths, whirlpool baths, irrigation systems, butterfly baths (hubbarda tank), aqua therapy, halliwick, bad ragaz ring method, and watsu are considered within the scope of hydrotherapy (Genç & Deveci, 2023). Immersion in warm water reduces sympathetic nervous system activation and increases parasympathetic nervous system activation. This effect elicits a relaxation response and reduces anxiety (Becker, 2009). Castro-Sánchez et al. revealed that 40 sessions of Ai-Chi exercise showed significant improvements in depression scores of multiple sclerosis patients (Castro-Sánchez et al., 2012). In studies examining the effect of hydrotherapy on anxiety and depression for different diseases in the literature, it was determined that it reduced anxiety and depression (Latorre-Román et al., 2015; Dinç Yavaş et al., 2021).

Another therapy that affects the level of anxiety and depression of individuals is balneotherapy. There are many balneological applications in spas. Balneotherapy is among the most commonly used treatment methods. Balneotherapy is defined as the use of baths (in bathtubs or pools) containing thermal mineral water from natural sources, with a temperature of at least 20 °C and mineral content of at least 1 g/L, and is applied as a cure (Fioravanti et al., 2017; Karagülle & Karagülle, 2015). The fact that balneotherapy is applied in the form of a cure makes hot springs an ideal environment not only for physical health but also for mental health by getting away from the stress and fatigue of daily life. It is used not only for the treatment of diseases but also by many people who want to live a healthy life and slow down aging (Özkuk et al., 2018). Dubois et al. investigated the efficacy of balneotherapy against paroxetine, a selective serotonin reuptake inhibitor, in patients with a generalized anxiety disorder (GAD). As a result of the study, it was found that the change in anxiety scores of balneotherapy patients was more advantageous (Dubois et al., 2010). The effect of spa treatments on salivary cortisol levels, which is considered as a stress marker, was examined, and it was reported that spa treatments have the potential to affect salivary cortisol levels in healthy or diseased individuals (Antonelli & Donelli, 2018). It was found that pain, mood, sleep, and depression symptoms improved after the balneotherapy cure was applied to healthy older adults (Latorre-Román et al., 2015). Özkuk et al. also found a more significant decrease in anxiety after balneotherapy and reported that this may be due to the interaction between pain and anxiety (Özkuk et al., 2018).

This study aims to provide a synthesis of evidence from randomized controlled trials published over the last two decades to determine the effectiveness of hydrotherapy and balneotherapy on anxiety and depression.

Method

This research is a systematic review and meta-analysis. The preparation of the study protocol and reporting of the manuscript were carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2021). Before the review, the study protocol was registered in the International Register of Prospective Systematic Reviews (PROSPERO) with accession number CRD42023448993.

Research question

In the current systematic review and meta-analysis, the PICOS tool was applied to develop a search strategy by PRISMA recommendations: (P) Population: Adult individuals aged 18 years and older; (I) Intervention: Hydrotherapy and balneotherapy; (C) Comparison: Active control or waiting list; (O) Outcome: Depression and anxiety (S) Study design: Randomized controlled trials.

Search strategy

The literature was searched in PubMed (MEDLINE), Cochrane, Scopus, Web of Science, and CINAHL databases for the last 20 years (2003–2023) between 15 October and 15 November 2023. The following Medical Subject Headings (Mesh) and free text terms were used to search the databases: (“anxi*” OR “panic disorder” OR “phobia” OR “depression” OR “depressive symptoms” OR “depressive disorder” or “major depressive disorder” OR “depressive syndrome”) AND (“hydrotherapy” OR “balneotherapy” OR “thalassotherapy” OR “spa therapy” OR “thermotherapy” OR “phytothermotherapy” OR “aquatic” OR “hydrogalvanic” OR “cryo” OR “pool exercise” OR “water-based” OR “pool-based” OR “stanger” OR “mud” OR “thermal water” OR “bath” OR “peloid” OR “natural therapeutic gas” OR “radon”). Only articles in English are included.

Eligibility criteria

Inclusion criteria for the analyses were 1) articles in English, 2) randomized controlled trials, 3) a sample of adults aged 18 years and older, 4) a sample diagnosed with anxiety or depression according to DSM-V, 5) a sample of healthy/patient individuals in whom anxiety or depression symptoms were measured, 6) studies describing balneotherapy or hydrotherapy as interventions, 7) studies reporting anxiety and depression severity assessed by a valid and reliable scale, 8) studies reporting anxiety and depression severity as mean, standard deviation, 9) studies published in 2003 or later. Control groups may include any form of intervention, including a control intervention (therapy, education) or usual care. The exclusion criteria for this analysis were 1) qualitative studies, correlation studies, cross-sectional studies, case–control studies, and cohort studies 2) studies with a population of children or adolescents.

Study selection

All references obtained through the search strategy were exported with the reference management software Endnote X9 and duplicate references were removed. The identification of the studies to be included in this review was carried out independently by the researchers according to the inclusion and exclusion criteria. Firstly, title/abstract screening was carried out by two independent authors. Studies with titles/summaries that did not meet the inclusion criteria were excluded at this step. Eligible studies were saved in a template created in Excel so that the full text could be read and evaluated. This template consisted of study details (author, publication year, country), inclusion or exclusion status, and reasons for exclusion. Full-text reviews of data extraction, methodological quality assessment, and analysis of included studies were performed by two independent authors. Any disagreements were resolved by discussing the full text of the article. The PRISMA Flow Diagram of the study selection process is given in Fig. 1.

Fig. 1
figure 1

Diagram of selection of studies

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Data extraction

Data extraction was carried out by two independent authors to obtain the research data. The information extracted included first author, year of publication, country, sample size and characteristics, intervention type, intervention, and control group, measurement tools used, and results.

To minimize the risk of bias, the literature search, selection of articles, data extraction, and quality assessment of the articles were carried out separately by two researchers. Any disagreement was resolved by discussing the full text of the article.

Quality assessment

The quality assessment of the studies was performed independently by two authors using the Joanna Briggs Institute critical appraisal tools. The “JBI Critical Appraisal Checklist for Randomized Controlled Trials” consisting of 13 items was used for the quality assessment of randomized controlled trials (Barker et al., 2023). Each item in the checklists was coded as yes, no, uncertain, or not applicable. In the checklist, items with “no” and “uncertain” answers received 0 points, while items with “yes” answers received 1 point. The full text of all included studies were analyzed and the studies were scored as a result of the review. Quality scores were given by two independent authors (SK and MY). There was 91.5% inter-rater agreement for quality scores. All discrepancies were discussed and reconciled by the reviewers.

Meta-analytical method

Stata 16.0 software was used for meta-analysis. Heterogeneity between the included studies was evaluated with I2. If the I2 statistic was below 0.50, it was accepted as low heterogeneity and a fixed effects model was used. Mean difference (MD) and standardized mean difference (SMD) were calculated for continuous variables. All tests were calculated with two-tailed tests and a p-value less than 0.05 was considered statistically significant. Begg’s test and Egger’s test were used to assess publication bias, and when the result of the test was p < 0.05, publication bias was considered to be present.

Results

Included studies

As a result of the search in electronic databases, 6,261 articles were found. After removing duplications, 5.431 articles remained. After title/abstract screening, 195 articles were identified as review articles. Of these studies, 178 were excluded from the meta-analysis because they were not randomized controlled trials (n = 73), did not report depression and anxiety outcomes with mean and standard deviation, or were ongoing randomized controlled trials (n = 23), the sample did not consist of adults (n = 8), did not report depression and anxiety (n = 26), and the intervention was not hydrotherapy or balneotherapy (n = 48) (Fig. 1). Seventeen studies were included in the meta-analysis.

Characterization of studies

The studies included in the meta-analysis included six countries. Brazil (Aidar et al., 2018; Assis et al., 2006; Britto et al., 2020; Cavalcanti et al., 2019; Fonseca et al., 2021; Taglietti et al., 2018), Turkey (Ardiç et al., 2007; Bağdatlı et al., 2015; Kurt et al., 2016; Taşkın & Ergin, 2022; Yolgösteren & Külekçioğlu, 2021), Spain (Acosta-Gallego et al., 2018; Pérez-de la Cruz, 2019; Tomas-Carus et al., 2008), Sweden (Hägglund et al., 2017), South Korea (Kim et al., 2012) and Germany (Naumann et al., 2020). There were a total of 977 participants, 455 participants were in the mind–body therapy group and 522 participants were in the control group. The largest sample studied 128 participants (Cavalcanti et al., 2019) and the smallest sample studied 21 participants (Ardiç et al., 2007). Among the 17 eligible studies, 12 included hydrotherapy (Acosta-Gallego et al., 2018; Aidar et al., 2018; Assis et al., 2006; Britto et al., 2020; Cavalcanti et al., 2019; Fonseca et al., 2021; Hägglund et al., 2017; Kim et al., 2012; Pérez-de la Cruz, 2019; Taglietti et al., 2018; Taşkın & Ergin, 2022; Tomas-Carus et al., 2008), 5 (Ardiç et al., 2007; Bağdatlı et al., 2015; Kurt et al., 2016; Naumann et al., 2020; Yolgösteren & Külekçioğlu, 2021) involved balneotherapy (Table 1).

Table 1 Summary characteristics of included studies
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Effect sizes

Anxiety symptoms

We included 8 studies reporting anxiety as a mental health outcome. The analysis revealed a significant effect and moderate heterogeneity (effect size of [SMD = 0.46 (95% CI 0.27 to 0.65), p = 0.00; I2 = 40.64%]). Hydrotherapy and balneotherapy interventions had a medium effect on reducing anxiety scores (Fig. 2).

Fig. 2
figure 2

Forest plots of the relationship between hydrotherapy/ balneotherapy and depression, anxiety

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Depression symptoms

We included 15 studies reporting depression as a mental health outcome. The analysis revealed a significant effect and low heterogeneity (effect size of [SMD = 0.53 (95% CI 0.38 to 0.67), p = 0.00; I2 = 0.00%]). Hydrotherapy and balneotherapy interventions had a medium effect on reducing depression scores (Fig. 2).

Subgroup analysis

All eligible articles were categorized by intervention type for anxiety and depression as shown in Fig. 3. In the subgroup analyses by intervention type for depression, a fixed effects model was used in the analysis due to small heterogeneity between studies (p = 0.69, I2 < 50%). It was found that applying hydrotherapy or balneotherapy intervention did not make a difference in reducing depression scores [SMD = 0.53, 95%CI (0.38, 0.67), p = 0.23]. In the subgroup analyses by intervention type for anxiety, the fixed effects model was used in the analysis since there was medium heterogeneity between the studies (p = 0.11, I2 = 40.64%). Balneotherapy intervention was found to be effective and statistically significant in reducing anxiety scores [SMD = 0.46, 95%CI (0.27, 0.65), p = 0.01].

Fig. 3
figure 3

Forest plots of the relationship between the number of intervention type and depression, anxiety. 1: Hydrotherapy, 2: Balneotherapy

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Publication bias

Funnel plot, Begg test, and Egger test were used to evaluate publication bias. No publication bias was found as a result of the Begg test (p = 1.000) and Egger test (p = 0.561) for anxiety. For depression, no publication bias was found as a result of the Begg test (p = 0.620) and Egger test (p = 0.539). According to the funnel plot graph, it was observed that the studies were symmetrically distributed (Fig. 4).

Fig. 4
figure 4

Funnel plots

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Reporting quality

The scores for the methodological quality of all studies included in the systematic review ranged from 5 to 12 (Table 2). The methodological quality of 5 studies was below 50% (Aidar et al., 2018; Ardiç et al., 2007; Kim et al., 2012; Taşkın & Ergin, 2022; Yolgösteren & Külekçioğlu, 2021). In 8 of the eligible studies, blinding of outcome assessors (Bağdatlı et al., 2015; Britto et al., 2020; Fonseca et al., 2021; Kurt et al., 2016; Pérez-de la Cruz, 2019; Taglietti et al., 2018; Tomas-Carus et al., 2008; Yolgösteren & Külekçioğlu, 2021) and blinding of outcome assessors and participants in 1 study (Assis et al., 2006).

Table 2 Quality assessment of the included studies
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Discussion

This systematic review and meta-analysis examined the relationship between hydrotherapy and balneotherapy and anxiety and depression symptoms in adults. The results showed that hydrotherapy and balneotherapy were significantly associated with lower anxiety and depression symptoms.

The results of this study suggest that hydrotherapy and balneotherapy interventions provide a significant improvement in depressive symptoms of adult individuals. Castro-Sánchez et al. revealed that 40 sessions of Ai-Chi exercise showed significant improvements in depression scores of multiple sclerosis patients (Castro-Sánchez et al., 2012). In a study conducted by Evcik et al. with 63 patients with fibromyalgia syndrome, water therapy was found to be effective in improving depression (Evcik et al., 2008). Latorre-Román et al. reported that balneotherapy was effective in the severity of depression in healthy adults (Latorre-Román et al., 2015). Dinç Yavaş et al. showed that standard balneotherapy and exercise programs had a positive effect on depression (Dinç Yavaş et al., 2021).

The results of the current study support our findings. Most of the studies that reported depression as a mental health outcome (14 out of 15 studies) did not report any concurrent intervention. This provides an important opportunity to evaluate the unique effects of hydrotherapy and balneotherapy. While 14 of the studies reporting depression as a mental health outcome described depressive symptoms associated with chronic diseases, only 1 evaluated the effectiveness of interventions in patients with depression. Therefore, it should be carefully considered whether existing interventions reduce depression by affecting the clinical picture of chronic diseases or whether they are directly effective on depression. Subgroup analysis showed that the type of intervention did not differ in improving depressive symptoms of adult individuals. Although balneotherapy utilizes the chemical content of water, it is based on similar mechanisms as hydrotherapy. Since both interventions may benefit from similar physical properties of water (temperature, pressure), they may have similar effects on depression (Fritsch et al., 2022).

The results of this study show that hydrotherapy and balneotherapy interventions provide a significant improvement in anxiety symptoms of adult individuals. Dubois et al. reported that balneotherapy provided a significant improvement in the anxiety scores of patients with generalized anxiety disorder compared to paroxetine (Dubois et al., 2010). A review of the literature on the effectiveness of balneotherapy reported that balneotherapy improved depression and anxiety (Clark-Kennedy et al., 2021). In the study by Im and Han, whirlpool hydrotherapy was found to reduce anxiety significantly more than hot compresses (Im & Han, 2013). In a systematic review of the effectiveness of hydrotherapy during labor, it was found that hydrotherapy reduced maternal anxiety (Shaw-Battista, 2017). The results of the current study support our findings. In a systematic review and meta-analysis investigating the effectiveness of hydrotherapy and balneotherapy in fibromyalgia syndrome, it was found that both intervention types did not show a significant effect on depressive symptoms (Naumann & Sadaghiani, 2014).

The current finding contradicts our study result. Most of the studies that reported anxiety as a mental health outcome (7 out of 8 studies) did not report any concurrent intervention. This provides an important opportunity to evaluate the unique effects of hydrotherapy and balneotherapy in reducing anxiety. Subgroup analysis showed that balneotherapy was more effective in improving anxiety symptoms in adults. Since balneotherapy (n = 35) was evaluated with a smaller sample size than hydrotherapy (n = 185), the results of the study on the effectiveness of balneotherapy should be evaluated with caution.

Limitations

This meta-analysis has some limitations. Firstly, the methodological quality of the studies included in the meta-analysis differs from each other. Only 8 studies reported that outcome assessors and 1 study reported that outcome assessors and participants were blinded. In some studies, the randomization method was not explained. In addition, some studies did not provide adequate explanations about the participants who dropped out of the study or did not examine whether the dropouts made a difference in the analyses. These methodological quality problems limit the interpretation of the results. Secondly, the meta-analysis is limited to studies involving the adult population with depression and anxiety symptoms. Except for 1 study including a sample followed up with a diagnosis of depression, the other studies were limited to studies that determined the level of anxiety and depression with self-report scales. The results should be interpreted with caution due to studies conducted with different patient populations. Third, there is a diversity of interventions in the control groups compared. Different interventions make it difficult to generalize and interpret the results; it makes it difficult to determine the true effect of hydrotherapy and balneotherapy.

Conclusion

This study shows that hydrotherapy and balneotherapy reduce depression and anxiety scores in adult individuals. It was found that the type of intervention did not make a difference in improving depression scores of adult individuals, and balneotherapy was a more effective intervention in reducing anxiety scores.