Association between before-bedtime hot-tub bathing and sleep quality in real-life settings among community-dwelling older adults

Abstract

Objectives: This study aimed to provide insights on the effects of hot-tub bathing on sleep quality under real-life conditions, accounting for various factors such as bathing behaviors, environmental influences, and individual characteristics.

Methods: We analyzed the association between hot-tub bathing and subsequent sleep in 2252 older adults (mean age, 68.8 years). Objective and self-reported sleep quality were assessed using actigraphy and the Pittsburgh Sleep Quality Index, respectively. Wrist and abdominal skin temperatures were recorded at 3- and 1-minute intervals, respectively, excluding and including the bathing period. The distal-proximal skin temperature gradient, an index of heat dissipation, was calculated as wrist skin temperature minus abdominal skin temperature.

Results: Multivariable models showed that individuals who bathed had significantly higher actigraphic sleep efficiency (1.3% [95% CI: 0.3-2.4], P = .013), shorter actigraphic wake after sleep onset (3.3 minutes [95% CI: 1.0-5.7], P = .005), higher distal-proximal skin temperature gradient after bedtime (0.26°C [95% CI: 0.11-0.41], P = .001), and lower odds of poor self-reported sleep quality (Odds ratio 0.73 [95% CI: 0.58-0.91], P = .006) compared with those who did not bathe, after adjusting for age, sex, body mass index, income, physical activity, day length, indoor and outdoor temperatures, and other confounders. Among bathers, immersion duration and abdominal skin temperature (surrogate for bathtub temperature) exhibited a negative interaction in relation to actigraphic sleep efficiency.

Conclusions: In real-world situations, hot-tub bathing was positively associated with actigraphic sleep metrics. Our findings can be used in future interventional studies to determine optimal hot-tub bathing conditions for improving sleep quality.

Keywords: Actigraph; Distal-proximal skin temperature gradient; Hot water bathing; Passive body heating; Pittsburgh Sleep Quality Index.