Night-time hot spring bathing is associated with a lower systolic blood pressure among Japanese older adults: A single-institution retrospective cohort study

Abstract Hot spring bathing is practiced helping manage hypertension. We analyzed patients’ medical records to investigate the preventive effects of hot spring bathing on hypertension with the aim of identifying a novel approach to prevent and manage hypertension. The study cohort comprised 99 patients aged ≥ 65 years who were admitted to the Department of Internal Medicine of Kyushu University Beppu Hospital between December 1, 2021, and November 30, 2022; who could walk by themselves; and who used hot springs for 3 days or more. We retrospectively calculated the odds ratios (OR) and 95% confidence intervals (CIs) of the influence of night-time hot spring bathing using the multivariate logistic regression model. The changes in both systolic and diastolic blood pressure were significantly decreased in the night-time bathing group (n = 21) compared to those in the noontime (n = 26) and afternoon (n = 52) groups. The female sex (OR 7.540; 95% CI 4.280–13.30), hypertension (OR 0.397; 95% CI 0.245–0.644), and arrhythmia (OR 12.20; 95% CI 5.340–28.00) were independently and significantly associated with night-time hot spring bathing. Night-time hot spring bathing was significantly associated with a reduced systolic blood pressure in older adults. Prospective randomized controlled trials on night-time hot spring bathing as a treatment for hypertension are warranted to investigate whether night-time hot spring bathing can prevent hypertension among adults aged ≥ 65 years.