ABSTRACT
Background: The traditional Japanese style of soaking in a hot bath is a lifestyle custom for many citizens, no study had ever investigated the association between bathing as a lifestyle practice and the onset of long-term depression. Through a large-scale six-year longitudinal study, we aimed to determine whether tub bathing as a lifestyle custom plays a role in preventing the onset of long-term depression. Methods: Of 11,882 individuals who responded to surveys conducted in 2010 and 2016 as part of the Japan Gerontological Evaluation Study (the JAGES) project, we analyzed 6,452 and 6,465 individuals for whom information was available regarding summer bathing frequency and winter bathing frequency, respectively; all of these individuals were independent, had a Geriatric Depression Scale (hereafter, “GDS”) score of ≤4, and did not suffer from depression. The cohort study involved dividing participants into a group of those who bathed 0-6 times a week and a group of those who bathed ≥7 times a week and determining the percentages of individuals who developed depression based on their GDS scores six years later. Multiple logistic regression analysis was performed to determine odds ratios for the association between depression onset and tub bathing. Results: For individuals who tub bathed ≥7 times a week, the odds ratios for depression onset versus individuals who bathed 0-6 times a week in summer and winter were 0.84 (95% confidence interval, 0.64-1.10) and 0.76 (95% confidence interval, 0.59-0.98), respectively. Tub bathing ≥7 times a week in winter significantly reduced the risk of depression onset. Conclusions: New-onset depression was shown to be infrequent in older adults who bathe in a tub frequently. Tub bathing was suggested to potentially contribute to the prevention of depression in the elderly.