Materials and methods

Missing data

Study authors were contacted and missing data obtained through personal communication (Fig. 1).

Fig. 1

Flowchart of the review and meta-analysis of randomised controlled trial (RCT) studies

Results

Systematic review

The literature search identified 122 studies. Among these, we found 18 possibly relevant studies for data retrieval according to the initial inclusion criteria (clinical trials) (Szucs et al. 1989; Konrad et al. 1992; Kovacs and Bender 2002; Holló et al. 2004; Balogh et al. 2005; Bender et al. 2007; Balint et al. 2007; Gaal et al. 2008; Olah et al. 2008; Zámbó et al. 2008; Nagy et al. 2009a, b; Kulisch et al. 2009; Olah et al. 2010, 2011; Tefner et al. 2012; Horvath et al. 2012; Kovacs et al. 2012). Data from 1,199 subjects (patients and controls) of the 18 clinical studies were evaluated. Dropouts comprised 7.1 % (n  = 85) of all patients, and a single adverse event (an allergic reaction to sulphur) occurred in only one study. The main causes of discontinuation were poor compliance and intercurrent disease.

 

Knee osteoarthritis

Three randomised, double blind, tap-water-controlled studies were identified, including the first trial of this kind published in English (Szucs et al. 1989). Immersion in thermal mineral water resulted in significant improvement of the clinical indices, namely pain [measured with a visual analogue scale (VAS)] and function [rated with the Western Ontario and McMaster Universities (WOMAC) scale] after balneotherapy (Szucs et al. 1989; Kovacs and Bender 2002; Balint and Szebenyi 1997; Gaal et al. 2008) (Table 1).

Table 1

Effect of balneotherapy on knee osteoarthritis. WOMAC Western Ontario and McMaster Universities index, RCT randomised controlled trial

 

Hand osteoarthritis

The two RCTs (one single blind and one double blind) showed that balneotherapy is beneficial for patients with hand osteoarthritis, in both the short and the long term. This was confirmed by the improvement of subjective and objective parameters [grip strength, pinch strength, Health Assessment Questionnaire (HAQ) score, morning joint stiffness, swollen joint count, tender joint count, the Short Form-36 (SF-36), HAQ-DI, Australian/Canadian Hand Osteoarthritis Index (AUSCAN), and Euro Qol Group (EQ5D) scores], without adverse events (Kovacs et al. 2012; Horvath et al. 2012) (Table 2).

Table 2

Effect of balneotherapy on hand osteoarthritis. VAS Visual analogue scale, HAQ Health Assessment Questionnaire, SF-36 Short Form-36, AUSCAN Australian/Canadian Hand Osteoarthritis Index, EQ5D Euro Qol Group scores

 

Chronic low back pain

One double blind and two single blind, tap water-controlled studies were published along with an RCT and a prospective study. The first three studies showed the beneficial effect of thermal mineral water compared with tap water. Both the clinical indices and the quality of life parameters improved significantly in the active treatment groups. The use of tap water as control is a rarity in the literature on the evaluation of mineral waters for low back pain. In a study with 1-year follow-up, analgesic consumption recorded at the last visit was significantly lower in the balneotherapy group compared to the controls (Konrad et al. 1992; Balogh et al. 2005; Gaal et al. 2008; Kulisch et al. 2009; Tefner et al. 2012) (Table 3).

Table 3

Effect of balneotherapy on chronic low back pain

 

Underwater traction treatment

Underwater traction (also known as weight bath therapy) was introduced by the Hungarian physician, Károly Moll (Moll 1953) In a controlled study of patients suffering from cervical and lumbar degenerative disc disease, underwater traction reduced pain intensity (VAS), increased spinal mobility, and improved the quality of life (Olah et al. 2008) (Table 4).

Table 4

Effect of underwater traction therapy on neck and lumbar pain

 

Chronic pelvic inflammatory disease

A 3-week course of balneotherapy was beneficial as an add-on intervention in the management chronic pelvic inflammatory disease. The improvement of clinical parameters was significantly greater with thermal mineral water than with tap water (Zámbó et al. 2008) (Table 5).

Table 5

Effect of balneotherapy on chronic inflammatory pelvic disease

 

Physiological effects

 

Effect of radon baths on the endocrine system

In Hungary, some mineral waters contain small amounts of radon, which had no significant effect on endocrine parameters. According to another study, radon speleotherapy had a minor influence on the endocrine system in patients suffering from chronic lung disease (Nagy et al. 2009a, b) (Table 6).

Table 6

Effect on endocrine parameters of exposure to radon in a spa bath and in healing caves

 

Effects on inflammatory and metabolic indices

Four studies investigated changes in inflammatory and metabolic indices. One controlled study found that mineral water had a more beneficial effect on antioxidant status than tap water. In hypertensive patients, the differences between baseline and post-treatment HbA_1C levels were more pronounced in the balneotherapy group than in the controls. The C-reactive protein levels in hypertensive patients decreased significantly after balneotherapy. In a study of patients with psoriasis, no change of beta-endorphin levels could be detected during balneo-phototherapy (Holló et al. 2004; Bender et al. 2007; Olah et al. 2010, 2011) (Table 7)

Table 7

Effect of balneotherapy on inflammatory and metabolic indices

Meta-analysis

Of the 18 clinical trials, 9 were excluded; 2 studies lacked a proper control group (Gaal et al. 2008; Holló et al. 2004); 1 study measured the effect of underwater traction and not that of balneotherapy (Olah et al. 2008). One additional study evaluated radon cave therapy and not balneotherapy (Nagy et al. 2009a, b). Following a more detailed review of these provisionally selected articles, a further five papers were excluded for the following reasons: one study lacked a relevant common endpoint (Szucs et al. 1989), and diverse outcome measures were assessed in at least four studies (Bender et al. 2007; Nagy et al. 2009a, b; Olah et al. 2010, 2011). Only studies with a symptom-specific outcome measure evaluated in at least four studies were selected. In the end, nine studies fulfilled the inclusion criteria for meta-analysis (Konrad et al. 1992; Kovacs and Bender 2002; Balogh et al. 2005; Balint et al. 2007; Zámbó et al. 2008; Kulisch et al. 2009; Horvath et al. 2012; Tefner et al. 2012; Kovacs et al. 2012). In view of the inclusion criteria, we selected “pain at rest” and “pain on loading” (both measured by VAS), because these were assessed in four and nine trials, respectively. If the paper did not specify what kind of pain was measured, we contacted the authors for clarification. We found that “pain on loading” improved significantly in seven out of the nine studies (Fig. 2). In this meta-analysis, the overall improvement of “pain on loading” was about 70–80 % (SMD 0.747, 95 % CI 0.931 to − 0.563, fixed effect; SMD 0.783, 95 % CI 1.144 to 0.422, random effect). “Pain at rest” improved in three out of four studies (Fig. 3); overall improvement was about 70 % (SMD 0.715, 95 % CI 0.998–0.433, random effect, SMD 0.715, 95 % CI 0.998–0.433 fixed affect). Using summarised analysis, the aggregate improvement of “pain on loading” and of “pain at rest” was significant. The heterogeneity test was significant for “pain on loading”. In seven trials, “pain on loading” improved significantly relative to the control group treated with heated tap water (Konrad et al. 1992; Kovacs and Bender 2002; Balint et al. 2007; Zámbó et al. 2008; Horvath et al. 2012; Tefner et al. 2012; Kovacs et al. 2012). However, in the remaining two trials, the improvement of “pain on loading” was significant also in the tap water group (Balogh et al. 2005; Kulisch et al. 2009). This finding may be explained by the cumulative soothing effect of warm water and concomitant interventions (such as electrotherapy). In these two studies, additional parameters, namely muscle spasm (measured by a manual method) and quality of life improved significantly in patients treated with thermal mineral water, as compared with the controls.

Fig. 2

Visual analogue scale (VAS) intensity of pain on loading

Fig. 3

VAS intensity of pain at rest

Discussion

In Hungary, balneotherapy has long been used as a traditional treatment, for the country is rich in thermal mineral waters. The majority of the published papers focus on balneotherapy for musculoskeletal disorders, although an increasing number of publications report its application in other clinical fields. Additional applications include inhalation treatment for laryngeal diseases and oncology rehabilitation programs, whereas the drug sparing effect of balneotherapy can be utilized in psychiatry (Dubois et al. 2010). Furthermore, it is useful in cardiovascular rehabilitation, especially because of the positive haemorheological effects of natural carbonated mineral water (Pagourelias et al. 2011). In the international medical literature, Kamioka et al. (2010) reviewed hydro- and balneotherapy papers published between 1990 and 2008. The authors could not draw any conclusions regarding balneotherapy, because of the diversity of outcome measures, the lack of proper control groups, and poor study design. Falagas et al. (2009) reviewed balneotherapy studies excluding hydrotherapy trials. They selected 29 RCTs of 1,720 patients; 8 of these evaluated balneotherapy in osteoarthritis, 4 in fibromyalgia, 4 in ankylosing spondylitis, 4 in rheumatoid arthritis, 3 each in psoriatic arthritis and chronic low back pain, and 1 in Parkinson’s disease. In 17 trials, pain decreased significantly compared to the control group, whereas in 8 trials there was no difference. The analgesic effect of balneotherapy lasted for 3 months in 9 studies of longer duration. In their meta-analysis of studies evaluating balneotherapy in osteoarthritis (including the study by Kovacs and Bender 2002), Verhagen et al. (2008) found only a few well-designed trials using appropriate statistical methods. The authors concluded that the effect of balneotherapy is “unproven” and called for additional well-designed studies. The systematic review by Forestier and Françon (2008) led to similar conclusions regarding balneotherapy trials of knee osteoarthritis. The small number of included patients and the poor methodology precluded any conclusions regarding the decrease of pain, improvement of function and quality of life following balneotherapy of patients with osteoarthritis of the knee. Harzy et al. (2009) reviewed 9 RCTs evaluating the balneotherapy of knee osteoarthritis. They found that pain measured by VAS decreased significantly for 8–12 weeks in six RCTs and for 20–24 weeks in two RCTs; articular function also improved significantly over the longer term. Recently, Forestier et al. (2010) published a multicenter RCT (conducted at three study sites) of 382 patients with knee joint osteoarthritis. The active group was treated with baths in thermal mineral water for 18 days in addition to massage, underwater massage, and mud packing. The control group received drugs and exercised. Balneotherapy was significantly superior in improving pain and joint function as measured by WOMAC, even after 6 months of follow-up. Pittler et al. (2006) published their meta-analysis of 5 RCTs (of 580 patients) appraising the effect of balneotherapy in chronic back pain. Active treatment comprised complex balneotherapy in 5 RCTs, but only immersion in thermal mineral water in one RCT. The controls—patients on the waiting list for balneotherapy—received drugs and exercised. The author rated the results as “encouraging” regarding the decrease of pain, and emphasised the need for further research. Since 2005, three tap water-controlled RCTs, all by Hungarian authors, have evaluated the effect of balneotherapy on back pain (Tefner et al. 2012; Kulisch et al. 2009; Balogh et al. 2005). The physical effect of temperature, buoyancy, and hydrostatic pressure, etc. during balneo- and hydrotherapy are well-established (Sramek et al. 2000). The chemical effects of balneotherapy, such as the absorption of minerals through the skin, is scarcely documented (Shani et al. 1985). The mode of action of thermal-mineral water treatment has been discussed in several papers, of which the work of Fioravanti et al. (2011) provides the most comprehensive overview. Only two countries—Turkey and Israel—have reviewed domestic balneotherapy research. Karagülle and Karagülle (2004) analysed 15 papers on studies evaluating the treatment of various musculoskeletal diseases at eight Turkish spa resorts. One of these studies examined the effect of mud pack treatment, whereas the others appraised that of bathing in thermal mineral water. The analgesic effect was significant in all balneotherapy trials. Katz et al. (2012) reviewed the research focused on Dead Sea balneo- and climatotherapy. Bathing in Dead Sea water and the exposure to UV radiation has a beneficial effect on psoriasis. Dead Sea balneo- and climatotherapy decreases pain, improves joint function and quality of life in rheumatoid arthritis, in ankylosing spondylitis, as well as in psoriatic arthritis and in osteoarthritis. Dead Sea balneotherapy did not increase blood pressure, as shown by ambulatory blood pressure monitoring (ABPM). Although our selection criteria identified only 18 Hungarian studies, all the remaining Hungarian papers, letters, and methodology publications appeared in important international journals (Balint and Szebenyi 1997; Bender et al. 2001, 2002; Somlai et al. 2007; Gerencsér et al. 2010; Varga 2011; Kavasi et al. 2011a, b; Varga 2012; Szendi et al. 2012). The Hungarian study of underwater traction (“weight-bath”) confirmed earlier biomechanical findings (Kurutz and Bender 2010).

Based on the numerous Hungarian and non-Hungarian tap water-controlled studies, we can state that thermal mineral water alleviates pain caused by different musculoskeletal diseases regardless of the qualitative and quantitative composition of mineral water. This finding may suggest that the minerals might act on cutaneous nerve endings, and thereby achieve long-lasting gate control; experimental skin biopsy studies could answer this question. The first tap water-controlled trial studying the effect of balneotherapy in chronic inflammatory gynaecological diseases was published by Hungarian authors. There are additional Hungarian studies about the effect of balneotherapy on the antioxidant system, as well as on inflammatory and metabolic parameters, which have been shown to remain normal even in patients with hypertension and obesity. The effects of exposure to radon in caves and in mineral water on some endocrine parameters were also studied. The Hungarian study of vertical underwater traction (weight bath—a balneotherapy modality introduced in the 1950s) was the first in the literature to demonstrate the clinical efficacy of this treatment in cervical and lumbar disc disease under controlled study conditions. We are aware, however, that only well-designed and implemented trials can prove or refute the efficacy of balneotherapy. Hungarian authors were the first to use balneotherapy with heated tap water as placebo control in a double-blind controlled study. This was possible because most of the Hungarian thermal mineral waters do not have a characteristic smell, and their colour can be imitated when necessary. Hungarian authors have aspired to conduct trials under ordinary, non-spa conditions, in local, ambulatory patients, keeping them in their everyday environment. The abundance of thermal springs in Hungary made it possible to realise this ambition.

Conclusion

Our review and the meta-analysis of nine articles appear to confirm that the studied Hungarian thermal mineral waters significantly reduce pain in degenerative joint and spinal disease, as well as osteoarthritis of the hand and knee, and that they also alleviate chronic low back pain.