London - Do we all need "pink noise" in our bedrooms? That’s what US researchers suggest, claiming that this type of meaningless sound, comparable to a waterfall, could help us enjoy a better night’s sleep - and even stall the onset of dementia.
Using noise to aid sleep is surprisingly common, with surveys showing as many as a quarter of adults prefer some kind of sound over dead silence to lull them into slumber.
Some of the most popular sounds are vacuum cleaners and hairdryers - indeed, many hairdryers come with a label warning "Do not use while sleeping" because of the fire risk involved. Thankfully, smartphone apps can now produce such sounds, too.
Scientists define these as types of "white noise" - which in its purest form, resembles radio static.
In 2005, US researchers from Rhode Island Hospital reported that when white noise was played in intensive care units, patients woke less frequently during the night. The simple explanation is that the noise masked environmental sounds, helping the patients to fall and stay asleep.
But now, scientists believe "pink nois"’ can perform significantly better. It is similar to white noise, but is thicker-sounding, with more low frequencies, which makes it similar to the torrent of a large waterfall.
There are now apps you can download to play pink noise (such as NoiseZ, Noise Generator: Full Spectrum and Pink Noise).
Over the past three decades, pink noise has fascinated researchers, as it is believed that it can induce brainwave patterns involved in deep sleep, when our brains work to consolidate new memories.
In a 2012 study, researchers at Peking University in Beijing hooked six people to electroencephalograms (EEGs), which recorded their brainwaves overnight as they slept.
When they were played pink noise, there was reduced activity in the brainwaves involved in alertness. This induces a deep - or "slow wave" - sleep that is known to help with long-term memory formation, they wrote in the Journal of Theoretical Biology.
Now, US researchers are investigating whether pink noise may help to stave off dementia. As we age, we tend to have less deep sleep as our slumber becomes lighter and more fragmentary.
One theory is that older brains produce less of the hormone melatonin, which induces sleep.
But brain cells associated with regulating sleep patterns, the ventrolateral preoptic nucleus, also slowly die off as we age, according to the journal Brain in 2014.
Professor Phyllis Zee, a neurologist who led the study, explains: "The effect for memory is related to the ability of the sound stimulus to enhance slow-wave sleep."
She adds: "The noise is just noticeable enough that the brain realises it’s there, but not enough to disturb sleep." Her team plans more tests over multiple nights.
However, other experts are yet to be convinced by the dementia benefits. "We don’t have scientific devices yet that can measure the differences in sleep quality accurately," says independent sleep researcher Dr Neil Stanley.
But he believes pink noise can help induce slumber, not least as it sounds so utterly meaningless.