Association Between Passive Body Heating by Hot Water Bathing Before Bedtime and Depressive Symptoms Among Community-Dwelling Older Adults.

OBJECTIVE: Passive body heating can have an antidepressant effect by activating warm-sensitive neural pathways associated with affective functions. Interventional studies showed that patients with depression had reduced depressive symptoms after passive body heating. However, the effect of hot water bathing at home on depressive symptoms in the general population remains unclear. Thus, we evaluated the association between objectively measured hot water bathing and depressive symptoms among older adults. DESIGN: Cross-sectional analysis. SETTING: A baseline survey of community-based cohort study in Japan. PARTICIPANTS: Community-dwelling older volunteers (n = 1,103; mean age: 72.0 years). MEASUREMENTS: The authors evaluated bathing conditions and distal skin temperature for 2 consecutive days. Depressive symptoms were defined as the 15-item Geriatric Depression Scale score of ≥6. RESULTS: Logistic regression showed that the no bathing group (adjusted odds ratio [OR] 2.60, 95% confidence interval [CI] 1.36-4.95, χ² = 8.40, degrees of freedom [df] = 1) and the either-day bathing group (adjusted OR 1.68, 95% CI 1.11-2.56, χ² = 5.89, df = 1) had higher odds of depressive symptoms than the both-day bathing group independent of potential confounders including age, sex, body mass index, alcohol intake, income, living alone, hypnotic use, diabetes, and physical activity. Shorter interval from bathing to bedtime was significantly associated with lower odds of depressive symptoms and higher nighttime distal skin temperature after adjusting for water temperature and duration. CONCLUSION: A higher frequency of hot water bathing and shorter interval from bathing to bedtime were associated with lower odds of depressive symptoms.