Frequency of Bathtub Bathing and Developing Dementia in Community-Dwelling Older Adults in Japan: A 9-Year Follow-Up in JAGES Cohort Study

• Published in: THE JOURNAL OF BALNEOLOGY, CLIMATOLOGY AND PHYSICAL MEDICINE Vol. 88; no. 2; pp. 73 - 82
• Main Authors: YANAGI, Natsuyo, KONDO, Katsunori, OJIMA, Toshiyuki, HAYASAKA, Shinya
• Format: Journal Article
• Language: Japanese
• Published: The Japanese Society of Balneology, Climatology and Physical Medicine 25.05.2025; 一般社団法人 日本温泉気候物理医学会
• Subjects: cohort study; dementia; older adults; tub bathing; コホート研究; 浴槽入浴; 認知症; 高齢者
• ISSN: 0029-0343; 1884-3697
• DOI: 10.11390/onki.2365

  Background: In recent years, Finnish sauna bathing has been reported to have beneficial health effects, such as reducing the risk of hypertension and dementia. Although tub bathing in Japan, which is used daily by the Japanese, differs from sauna bathing, there are a few reports on its potential effects in reducing the risk of cardiovascular disease and depressive symptoms, but no reports on dementia. Therefore, we aimed to investigate the association between bathing and incident dementia in Japanese community-dwelling older people using large longitudinal data.  Methods and Results: We used data from the Japan Gerontological Evaluation Study (JAGES), which included community-dwelling older people aged ≥65 years who were not certified for long-term care. The baseline survey was conducted in 2010, and the onset of dementia was assessed using records from Japan’s long-term care insurance system. After excluding respondents with missing data on bathing frequency in summer and winter separately, a total of 7,509 individuals were analysed for summer and 7,590 for winter. Bathing frequency was divided into two groups: low frequency (0-6 times/week) and high frequency (≥7 times/week). To examine the association between bathing frequency and incident dementia, we performed survival analysis using the competing risk model and calculated sub hazard ratios (SHRs) and 95% confidence intervals (CIs). During 9 years of follow-up, 1,430 (17.2%) cases of dementia were identified in 8,317 individuals. In the crude model, the high-frequency bathing group showed a significantly lower risk of incident dementia, and this association remained significant after full adjustment, with SHRs of 0.74 (95% CI: 0.62-0.88) in summer and 0.82 (95% CI: 0.70-0.97) in winter.  Conclusions: High-frequency bathing was associated with a lower risk of incident dementia among Japanese community-dwelling older adults. This finding suggests that tub bathing, one of the lifestyle habits of older people in Japan, may contribute to preventing dementia.