BackgroundCardiovascular diseases are a main cause of mortality worldwide. Spa bathing and immersion in thermoneutral water (ITW) have a long history in the treatment of cardiovascular risk factors.MethodsWe conducted a three-arm parallel-group, randomized controlled study to investigate the effects of frequent ITW on moderately elevated blood pressure (BP). Here, we report on the secondary outcomes, i.e. the influence of immersion in thermoneutral water on further cardiovascular risk factors: body mass index (BMI), waist circumference, blood lipids, fasting blood glucose and C-reactive protein. Patients (age 57.6 ± 9.6 years, BMI 29.5 ± 5.7 kg/m2) with mild to moderately elevated BP received ITW for 45–60 min in pools of thermal-mineral water at 34.0–36.0 °C four times a week for 4 weeks. One group (Bath1) reduced the intensity to one bath a week for a further 20 weeks, while the other group (Bath2) continued bathing four times a week. The control group was instructed to relax for 45–60 min four times a week for 24 weeks using a relaxation CD.ResultsThe secondary analysis of the intention-to-treat population (N = 59) did not show a significant reduction of BMI, waist circumference, blood lipids, fasting blood glucose or C-reactive protein in patients with a mild to moderately elevated BP after 4 and 24 weeks ITW, respectively. There were no significant differences between the groups.ConclusionThus, we did not find evidence to support our ITW program being an efficacious intervention to induce cardiovascular alterations in this population of hypertensive patients.Trial registrationDRKS00003980 at drks-neu.uniklinik-freiburg.de, German Clinical Trials Register (registration date 2012-07-10).Electronic supplementary materialThe online version of this article (doi:10.1186/s12906-016-1241-7) contains supplementary material, which is available to authorized users.

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