Changes in sleep profile on exposure to sodium chloride and artificially carbonated springs: a pilot study.
Sachiko Ito Uemura, Takashi Kanbayashi, Wakako Ito and 5 others
PMID 37131353WHAT IT FOUND
In eight healthy young men, baths before bed did not clearly shorten time to fall asleep or improve total sleep, but they increased a brain-wave marker of deep sleep in the first sleep cycle versus no bath.
Key findings
01Bathing raised core body temperature before bedtime, and the bathing groups then had lower core body temperatures during sleep than the no-bath group.
02Delta power per minute in the first sleep cycle, which the authors calculated as a marker of deep sleep, increased after bathing: 20.4 after sodium chloride spring, 20.7 after artificial carbonated spring, 18.1 after plain hot water, and 13.6 after no bath (p<0.01).
03Sleep latency, total sleep time, sleep stages, REM sleep, wake time after sleep onset, sleep efficiency and total delta power did not significantly differ between groups.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study included only eight healthy young men who completed the experiment, so it does not show what happens in women, older adults, people with insomnia, or patients. Participants and researchers were not blinded, and the sodium chloride spring room was warmer than the other rooms, so expectations and environment could affect the results. The study tested one acute bath, not repeated bathing, and used a portable single-channel EEG. It was a pilot with a small sample and no prior power calculation; the significant delta-power result did not translate into significant changes in sleep latency, total sleep time, sleep stages, wake time, sleep efficiency or subjective sleepiness. Hot spring effects cannot be separated from temperature, physical action and chemical composition, and the sodium chloride condition used a natural hot spring facility rather than a bathtub.
Declared interests
Partially supported by AMED and JSPS KAKENHI grants. Authors declared no conflicts of interest.
The easy way to misread this
Do not conclude that sodium chloride or artificially carbonated springs are better sleep treatments than a plain hot bath or a proven alternative to medication. The significant finding was a delta-power change in early sleep, while sleep latency and most sleep-stage outcomes were not significantly different, and the study had only eight healthy young men.