Category: Sleep

Bathing before bed is linked to falling asleep faster, sleeping for longer and sleeping more efficiently.

Having a bath or shower around 90 minutes before bedtime leads to the best sleep. Bathing before bedtime is linked to falling asleep faster, sleeping for longer and sleeping more efficiently, studies show. The best temperature for the bath or shower is between 104 and 109 degrees Fahrenheit (40-43 degrees Celsius).

Cooling the body’s core

Hot baths and showers work, slightly confusingly, because they end up lowering the body’s core temperature. The hot water stimulates the thermoregulatory system, which causes blood to move from the core to the hands and feet. This effectively cools the body’s core. A cooling body temperature helps signal to the body and brain that it is time to sleep. The reason is that our body temperature follows daily, or ‘circadian’, rhythms. Body temperature naturally fluctuates by around 2-3 degrees and is at its highest in the late afternoon and early evening. Around 90 minutes before bedtime, though, it is normally reduced by up to 1 degree. The body’s lowest temperature is achieved through the middle and later parts of sleep.

Reviewing the research

The conclusions come from a review of 17 separate studies that examined the connection between taking a bath or shower before bedtime and sleep quality. The results clearly showed the benefits of a hot shower or bath 1-2 hours before bedtime. Shahab Haghayegh, the study’s first author, said:

“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings. The only way to make an accurate determination of whether sleep can in fact be improved was to combine all the past data and look at it through a new lens.”

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The study was published in the journal Sleep Medicine Reviews (Haghayegh et al., 2019).

People in the study slept better and their memory was boosted.

Special sounds during sleep can improve sleep and boost memory.

The gentle sounds were timed to coincide with natural ‘brain waves’: the waves of electrical activity in the brain.

People in the study were able to recall 26 percent more words they had learned after being exposed to the sounds during sleep.

Dr Phyllis Zee, a study author, said:

“This is an innovative, simple and safe non-medication approach that may help improve brain health.

This is a potential tool for enhancing memory in older populations and attenuating normal age-related memory decline.”

Deep sleep is known to be critical for memory consolidation: the process by which memories are laid down for the long-term.

However, in older adults, the amount of time spent in deep sleep typically reduces.

The study compared the acoustic stimulation with sham treatments, which acted as a placebo.

Older individuals — who were targeted for the study — showed better sleep and enhanced memory only after the real acoustic stimulation.

The study’s authors explain their conclusions:

“Acoustic stimulation that was phase-locked to sleep slow waves in older adults had systematic effects on sleep indices and performance on a declarative memory test.

These results provide the first demonstration that acoustic stimulation alters SWA [slow wave activity or, colloquially, deep sleep] and can enhance word pair recall in older adults.

These results converge with other findings in young adults indicating that acoustic stimulation during sleep is a promising tool for altering SWA and enhancing sleep-dependent memory consolidation.”

The sound waves in the study were timed to coincide with people’s brain waves.

Their brain waves were read in real time and the sounds timed to help synchronise activity across the neurons.

Dr Nelly Papalambros, the study’s first author, said:

“The idea is to be able to offer this for people to use at home.

We want to move this to long-term, at-home studies.”

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The study was published in the journal Frontiers in Human Neuroscience (Papalambros et al., 2017).

Even good sleepers frequently experience insomnia.

Around one-quarter of Americans who are ‘good sleepers’ experience acute insomnia each year.

However, without treatment 75 percent recovered without developing persistent sleep problems.

Of the rest, 21 percent got on to have recurring bouts of insomnia.

The remaining 4 percent developed chronic insomnia.

Insomnia is defined as having trouble falling asleep or staying asleep for at least three nights a week across two weeks.

The condition becomes chronic when it continues for three months.

Dr Michael Perlis, study author, said:

“Whether caused by stress, illness, medications, or other factors, poor sleep is very common.

These findings reveal new insights about the paths that acute insomnia takes and can inform interventions that target poor sleep and help people recover sustained sufficient sleep.”

The study tracked 1,435 adults for a year.

All were initially defined as ‘good sleepers’: able to fall asleep within 15 minutes and not remaining awake for more than 15 minutes during the night.

The study’s authors conclude:

“The incidence rate of acute insomnia (3 or more nights a week for between 2 and 12 weeks) is remarkably high.

This said, most incident cases resolve within a few days to weeks. Incident chronic insomnia only occurs in about 2 in 100 individuals.”

Adaptive insomnia

So, why is insomnia so common?

It may be that insomnia in response to stressful situations helped keep our ancestors alive — after all, it is sub-optimal to be fast asleep in your cave when there’s a pack of wolves outside it.

The study’s authors explain:

“…it is possible that AI [acute insomnie] may be normative (i.e. expected as part of the natural rhythm of sleep/insomnia) , if not adaptive.

One way this might be true is that the AI that occurs with stress may be an unrecognized part of the fight-flight response; a necessary override to the normal two process regulation of sleep timing, depth and/or duration.

Put differently, stress induced insomnia may prohibit the systematic imperative for sleep under unsafe conditions.”

Unfortunately, the knowledge that periodic insomnia is normal doesn’t make it any less unpleasant.

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The study was published in the journal Sleep (Perlis et al., 2019).