Source: The Conversation – UK – By Robert MacKinnon, Clinical Scientist and Deputy Head of School for Psychology, Sports and Sensory Sciences, Anglia Ruskin University
Are you one of those people who can’t drop off to sleep if it’s “too quiet”? If so, you’re not alone. According to a 2023 survey of UK participants, 50% of people listen to some kind of noise to help fall asleep.
Many people have turned to pink, white or brown noise to help them drift off. But a new study has found listening to pink noise, an alternative to white noise, even to drown out irritating background sounds, can disrupt the quality of sleep you get.
What is pink noise?
Not all noises are equal though when it comes to sleep. Noises range from structured sound like music and speech, with patterns and meaning, through to others that have some arrangement and perhaps calming effect, like birdsong, ocean waves or wind chimes to noise with no order at all.
We can describe sounds by how much energy each frequency of the sound has. White noise is a totally random sound. Each different frequency in white noise has the same energy, so it sounds like a hissy continuous sound. A 2017 study found white noise seems to help some people concentrate.
Pink noise is different. Instead of equal energy at each frequency, the energy halves with every doubling of frequency (so 500Hz has twice the energy of 1000Hz). This mimics a lot of sounds in nature (like running water) and gives a deeper, more rumbly sound. It sounds less harsh than white noise.
You can also get brown noise – stop laughing – which is named after 18th-century scientist Robert Brown rather than anything bowel related. It is sometimes referred to as red noise instead. Higher frequencies have less energy
(500Hz has four times the energy of 1000Hz). It is even more bass-heavy than pink noise, sounding like heavy rain or a roaring waterfall.
What did the study find?
The new study by the University of Pennsylvania, sponsored by the US Federal Aviation Authority, compared the affect of pink noise and earplugs upon participants’ sleep when intermittent noise of planes flying overhead was played over a loudspeaker.
The control condition here was a noise-free night where the participants were monitored, but were not having their sleep interrupted. The researchers then tested the same participants under different conditions on different nights of their stay during the experiment. They measured brain activity, heart rate and muscle activity while participants slept, which allowed them to analyse the different stages of sleep.
The researchers first looked at how pink noise affected participants’ sleep when there was no other background noise and compared the effect to the control night. They found that pink noise led to a reduction of the amount of participants’ rapid eye movement (REM) sleep, which should make up about a quarter of our sleep. REM sleep isn’t considered a restful type of sleep but it is the sleep state in which we dream. REM is important for memory formation, brain plasticity and emotion regulation, particularly for children.
In the next phase of the experiment, they found that the environmental noise, by contrast, reduced the amount of so-called N3 sleep compared to the control night. This is the deepest non-REM type of sleep. It is where the body grows and repairs itself, and about a quarter of sleep should normally be of this type too.
The researchers then tried to block the environmental noise. When they used earplugs to see if they would help participants’ sleep, they worked well, restoring about three quarters of the lost N3 sleep. When they tried pink noise to see if it could help, they found that it actually made the sleep structure worse, reducing both N3 and REM sleep.
So is silence best?
Perhaps, and especially for babies and toddlers whose brains are still undergoing the most change and development. For adults though, there does seem to be some suggestion playing nighttime sounds helps. A 2022 review found that there was widespread, but low-quality, evidence that sounds at night time (especially pink noise) helps with the amount of sleep people get and also that people felt that it was better quality sleep. This was self-reported, rather than measured using equipment like in the new study from Pennsylvania, which might help to explain the different findings.
Other things may stop you getting to sleep. Many people experience tinnitus, a ringing or buzzing sound in the head or ears, which can be worst before bed and affect sleep quality. A silent room can make it seem even louder. Some people find a background sound, whether a “colour” of noise, nature sound, music or a podcast, helpful here to get to sleep. Being able to pick which “colour” of random sound you prefer has been shown to help people with tinnitus.
However, there are reports of potential harm from using any of these “random” sounds to help with tinnitus instead of more patterned noise like music or speech. This is because the random sounds can show the same kind of effect as ageing does on the brain. How this works, whether potential noise-induced hearing loss acts as an step in the chain, and how broadly it happens, remain areas of investigation.
So it’s not quite time to put the story of sleep quality and noise to bed just yet. In the meantime, trying some earplugs if there is unwanted sound, or keeping any noises calm, not too loud and relaxing for you may be the best bet for a good night’s sleep.
Robert MacKinnon does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
– ref. Pink noise: what is it and can listening to it make your sleep worse? – https://theconversation.com/pink-noise-what-is-it-and-can-listening-to-it-make-your-sleep-worse-275179