Tag Archives: Warm

Baby bath.

A warm bath 1-2 hours before bedtime helps improve sleep quality, meta-analysis shows

Researchers at the University of Texas at Austin (UoT) say that a warm bath one or two hours before going to bed is just what you need for a good night’s sleep.

Baby bath.

Image via Pixabay.

A review of thousands of previous studies on the subject allowed the authors to link bathing and showering (water-based passive body heating) with improved sleep quality. Bathing 1-2 hours before bedtime in water of about 104-109°Fahrenheit (40 to 43°C) seems to yield the best results.

A nice, relaxing bath

“When we looked through all known studies, we noticed significant disparities in terms of the approaches and findings,” said Shahab Haghayegh, a Ph.D. candidate in the Department of Biomedical Engineering at UoT and lead author on the paper.

“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.”

The team collaborated with members from the UoT Health Science Center at Houston and the University of Southern California to review 5,322 studies on the effects of water-based body heating on sleep. From this body of research, they extracted information published in journals meeting predefined inclusion and exclusion criteria (so as to ensure their data was reliable). The team quantified the effects of bathing by looking at several indicators:

  • Sleep onset latency: how much time it takes to fall asleep
  • Total sleep time
  • Sleep efficiency: how much time people spend asleep compared to the amount of time they want to sleep
  • Subjective sleep quality.

Overall, the team reports, the optimum bath temperature to increase sleep quality revolved around 104-109°Fahrenheit (40 to 43°C). If taken 1-2 hours before bed, such a bath also reduced the time needed to fall asleep by an average of 10 minutes.

The team writes that body temperature is, in part, governed by our bodies’ sleep/wake cycle (the ‘circadian clock’) that is handled by the hypothalamus. Our bodies are 2 to 3 degrees Fahrenheit warmer in the late afternoon/early evening than during sleep (at which point it is the lowest of the whole day). People on average experience a reduction in core body temperature of about 0.5 to 1°F an hour before their usual sleep time. It keeps dropping as we sleep, reaching the lowest point sometime between the middle and later part of our usual sleep duration. In the morning, or around the time one is used to waking up, core temperature begins to rise. Think of it as a kind of biological alarm clock.

The temperature cycle underpins the sleep cycle and is an essential factor in falling asleep rapidly, easily, and for ensuring high-efficiency sleep, the team notes. The team says that the optimal time to have a bath is 90 minutes before going to bed — this gives your body enough time to cool down sufficiently.

Warm baths and showers stimulate the body’s thermoregulatory system, they explain, which improves blood flow from the internal organs out to peripheral areas such as the limbs — where it dissipates heat. Therefore, baths taken 1-2 hours before bedtime aid the natural circadian process and increase the chances of falling asleep quickly and improve sleep quality.

The paper “Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis” has been published in the journal Sleep Medicine Reviews.

Commuters, traffic, and offices make cities hotter during the week

Humans have a much more direct impact on weather than you’d think. The huge number of commuters pouring into cities during the week actually makes them warmer and shifts local wind, rain, and cloud patters, a new study found.

Image credits Pat McKane / Pixabay.

During the week, all the people, cars, and operating buildings in cities pour out a lot of heat into the environment. Recently, Nick Earl at the University of Melbourne, Australia found that you can actually tell if it’s a workday or the weekend by the average temperature. Based on more than 50 years’ worth of recordings from Australia’s Bureau of Meteorology, Earl and his team showed that morning temperatures in Melbourne are typically 0.3 degrees C hotter on Thursday or Friday than on a Sunday.

“That’s just the average,” he says. “Some days will heat up more, if for example there isn’t much wind.”

It’s not surprising, given that the city sees some 250,000 extra people and heavy traffic every weekday compared to the weekends. All the air conditioning in office buildings also plays a part. This weekly cycle caught Earl’s eye in the first place.

“Nothing in nature occurs on a weekly cycle, so it must be due to human activity.”

Earl and his team have shown that Sydney, Brisbane, and Adelaide have similar weekly temperature cycles. Tokyo or Moscow also show the same cyclicity. Other weather phenomena, such as wind speeds, precipitation, and cloud cover also tend to be greater in urban centers during the week. These are effects of higher heat and pollution levels, Earl says.

“For example, warmer temperatures in the city create convection, which can suck in more air from outside, affecting wind speeds and direction,” he added.

Knowing how human activity impacts weather and average temperatures can help adapt to freak weather patterns and save lives. This can become especially useful in hot areas or countries, such as Australia, where heatwaves can claim the lives of a lot of people.

“For example, during heatwaves, you could ban cars from the city so that it doesn’t warm up as much.”

It could also help urban planners counteract the effect, for example by requiring roofing to be made of deflecting material which can cool down cities.

The paper will be presented at the annual conference of the Australian Meteorological and Oceanographic Society in Canberra next month.