2021 · Kato — Heat-retention effects of hydrogen-rich water bath assessed by thermography for humans
Super-Abstract
A hydrogen-rich bath keeps the body warm longer than a normal bath. Thermography on 24 healthy people showed, after identical bathing (41 °C, 10 min), markedly more heat retention — above all in the abdomen, thighs, arms and hands — as well as widened fingertip capillaries as a sign of better circulation. (Journal of Thermal Biology, 2021.)
Commentary
Hydrogen bath devices are sold commercially, but the heat-retention effect had hardly been cleanly studied — this study fills exactly that gap. 24 healthy people bathed under identical conditions (41 °C, 10 minutes) once in hydrogen-rich water (H₂ concentration 185–548 µg/L, redox potential −167 to −91 mV) and once in normal water (0.8 µg/L, +479 mV). A thermal imaging camera measured 30 and 60 minutes after the bath. Result: the H₂ bath retained markedly more heat — in this order: abdomen > thighs > arms > hands > feet. On the head, armpits and lower legs there was hardly any difference. In addition they measured the thickness of the fingertip capillaries: it was more dilated after the H₂ bath than after the normal bath — a sign that H₂ promotes circulation beyond the mere heat effect. Heat retention correlated weakly to moderately with body fat percentage and BMI and inversely with muscle percentage — but no more strongly than with the normal bath. In practical terms: the effect was present broadly across different body types. To be honest in the assessment: small sample (n = 24), healthy subjects, short observation, and the conclusion „circulation-promoting“ is derived indirectly from capillary thickness + thermography, not a direct blood flow measurement.
Key quotes
- „hydrogen-rich water bath ... brought about the heat-retention being more marked than those of normal water bath for several body-parts in the order as follows: abdomen > upper legs > arms > hands > feet“ — stronger heat retention in the H₂ bath, graded by body region
- „The thickness was expanded in the hydrogen-rich water bath more markedly than that in the normal water bath, suggesting that the hydrogen-rich water bath may have the hydrogen-based promotive effect ... on blood circulation of the whole body.“ — dilated fingertip capillaries as a sign of better whole-body circulation
- „The heat-retention after bathing can be noted as effects of the hydrogen-rich water bath, which is applicable for most of people widespread regardless of their body composition index.“ — the effect was present largely regardless of body build
Our assessment
Directly relevant for H₂ bath/wellness products (the H₂ bath as an application form alongside drinking water and inhalation). The study provides a concrete, everyday and easily communicable argument: noticeably longer warmth + a sign of better circulation. The stated H₂ concentrations (185–548 µg/L) and the strongly negative redox potential (−167 to −91 mV) are useful reference values for product communication. Limitations honestly: small sample (n = 24), only healthy subjects, short follow-up (max. 60 min), and the circulation claim is indirect (capillary thickness/thermography instead of a direct flow measurement). No clinical endpoints. Classification as pilot/mechanistic evidence in a wellness context — no medical cure promise.
Study design
- Type: clinical pilot study (thermographic, comparison of H₂ bath vs. normal bath) · n: 24 (healthy) · Duration: bath 10 min at 41 °C; measurement 30 and 60 min after the bath · H₂ delivery: full bath in hydrogen-rich water (185–548 µg/L H₂; ORP −167 to −91 mV) vs. normal water (0.8 µg/L; +479 mV)
- Result: stronger heat retention in the H₂ bath (abdomen > thighs > arms > hands > feet), little on the head/armpits/lower legs; significantly widened fingertip capillaries; weak/moderate correlation with body fat/BMI, inverse correlation with muscle percentage (individual p-values not reported in the abstract)
Abstract
Hydrogen-rich water bath devices are commercially available, but have been scarcely clarified for heat-retention effects. In this study, heat-retention effects of hydrogen-rich water bath were assessed by thermographic clinical trials, which employed twenty-four healthy subjects. The thermograms indicated that, under the same conditions (41 °C, 10-min bathing), hydrogen-rich water bath (hydrogen concentrations: 185-548 μg/L; oxidation-reduction potentials: -167 to -91 mV, versus 0.8 μg/L and +479 mV for normal bath, respectively) brought about the heat-retention being more marked than those of normal water bath for several body-parts in the order as follows: abdomen > upper legs > arms > hands > feet, for 30- and 60-min post-bathing, being in contrast to scarce heat-retention for head, armpits and lower legs. Then, as reflection to promotive effects on blood stream, we also examined the thickness of fingertip-capillary in hands. The thickness was expanded in the hydrogen-rich water bath more markedly than that in the normal water bath, suggesting that the hydrogen-rich water bath may have the hydrogen-based promotive effect, exceeding over mere heat retention-based effects, on blood circulation of the whole body. Meanwhile, the heat-retention in hydrogen-rich water bath weakly or moderately correlated with contents of the subcutaneous fat, whole body fat and body mass index, and inversely correlated with skeletal muscle rates, although their correlation degrees did not obviously exceed over normal water bath, with a poor relation with the basal metabolism rate. Thus, the hydrogen-rich water bath was suggested to exert heat-retention effects exceeding over normal water bath, in diverse body-parts such as abdomen, upper legs, arms and hands, via promotion to blood flow which was reflected by expanding the thickness of capillary. The heat-retention after bathing can be noted as effects of the hydrogen-rich water bath, which is applicable for most of people widespread regardless of their body composition index.
Source & links
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