Challenges of blinding in clinical balneology trials: a scoping review

Abstract

Background: In evidence-based medicine, randomized, placebo-controlled, double-blind clinical trials are considered the 'gold standard' of study design. Efforts must be made to advance evidence-based balneology in a similar manner. The objective of this scoping review was to assess the intervention types of experimental and control groups used in clinical balneology trials to map the proportion of open-label, single- and double-blind studies.

Methods: Eligibility criteria: i) prospective interventional clinical trial, ii) focused on the therapeutic effect of natural medicinal and mineral water, iii) administered head-out immersion, iv) compared with any other intervention or no treatment, v) in adult patients, and vi) with no restrictions on study design or language. Two authors independently searched the Medline, Embase and Cochrane databases for trials published in any language between 1990 and 12 February 2025.

Results: The 109, included trials were categorized into eight groups according to the treatment of the experimental and control groups and the use of blinding. Studies in the lower categories (1, 2, 3) completely lack blinding. In categories 4a-b-c, tap water control was used in parallel with medicinal/mineral water. Category 4c was the first category where the 'gold standard' of evidence-based medicine was implemented. Finally, in the last two categories (5a-b), validated placebo water was used. Low-category papers constituted the largest group, accounting for 74% of the total number of publications. From 1990 to the present, only 11% of publications chose the double-blind setup. Most higher category papers were published in Hungary. Over time, there has been no clear improvement in study design.

Conclusions: Future balneological research should prioritize rigorous experimental designs, particularly by incorporating validated placebo water and double-blind methodologies. Without these improvements, the ability to draw reliable conclusions about the true efficacy of balneotherapy remains limited.

Registration: The scoping review protocol was registered prospectively in OSF registries (Registration DOI https://doi.org/10.17605/OSF . IO/XHS4B, internet Archive link https://archive.org/details/osf-registrations-xhs4b-v1 , Date registered June 26, 2022).

Keywords: Balneology; Blinding; Clinical trial; Medicinal water; Mineral water; Scoping review.

Fig. 1

PRISMA 2020 flow diagram for new systematic reviews

Fig. 2

Total number of included papers by country. A: Austria; BIH: Bosnia; BR: Brazil; CN: China; DE: Germany; EE: Estonia; ES: Spain; ETH: Ethiopia; FR: France; HU: Hungary; IL: Israel; IS: Iceland; IT: Italy; JP: Japan; LT: Lithuania; MAR: Morocco; TR: Turkey

Fig. 3

Distribution of papers by water type

Fig. 4

Total number of papers published in each category

Fig. 5

Proportion and number of lower (1, 2, 3) and higher (4, 5) category papers by country. A: Austria; BIH: Bosnia; BR: Brasil; CN: China; DE: Germany; EE: Estonia; ES: Spain; ETH: Ethiopia; FR: France; HU: Hungary; IL: Israel; IS: Iceland; IT: Italy; JP: Japan; LT: Lithuania; MAR: Morocco; TR: Turkey

Fig. 6

Proportion and number of all papers in all categories by decades