While most adults need between seven and nine hours of sleep every 24 hours to function effectively, scientific research is shedding light on why a rare group of people can remain energised after remarkably little rest.
Recent genetic studies have found that specific inherited mutations allow natural short sleepers to function on as little as four hours of sleep without apparent ill effects. The findings suggest these mutations may protect against memory loss and cognitive decline, while opening up new possibilities for pharmaceutical development, reports BBC.
The discovery of natural short sleepers
For Aimee Pugh Bernard, an immunology professor at the University of Colorado, waking up at 4:30am after going to bed at around 10pm has been a lifelong routine.
Even after sleeping for just five hours, she remains energetic. She walks her dog, completes a one-hour gym session and works for 1.5 hours before 8am. Her father and brother follow similar sleep patterns.
In 2019, Bernard submitted a blood sample to a research team at the University of California, San Francisco (UCSF). Tests confirmed that she carries a rare genetic mutation linked to Familial Natural Short Sleep (FNSS), an inherited condition in which people go to bed at conventional times but wake up unusually early, sleeping between four and six-and-a-half hours.
According to the US National Sleep Foundation’s latest review of evidence, adults aged 26 to 64 generally need seven to nine hours of sleep a day, making FNSS carriers an unusual exception to the norm.
Protection against cognitive decline
One of the biggest questions surrounding FNSS is why carriers do not appear to suffer the usual consequences of sleep deprivation.
Dr Ying-Hui Fu, a molecular biologist at UCSF and the lead investigator, said genetic variations associated with FNSS appear to protect carriers against cognitive problems, including memory impairment.
In a 2019 study led by Dr Fu, mice engineered to carry an FNSS mutation slept less but showed protection against memory deficits. They were also less likely to develop a mouse model of Alzheimer’s disease.
Research involving humans has produced similar findings.
In a 2014 study, an international research team examined a pair of fraternal twins, only one of whom carried a short-sleep mutation. The carrier twin regularly slept about an hour less than his brother.
However, when both were kept awake continuously for 38 hours, the carrier twin recorded around 40 per cent fewer performance lapses than his sibling.
Despite sleeping less overall, he also obtained almost the same amount of non-REM slow-wave, or deep, sleep. This suggests that he gained similar biological benefits from a shorter period of sleep.
Pharmaceutical potential and genetic complexity
Scientists hope these genetic discoveries could eventually help develop treatments for sleep disorders or support military personnel who are required to operate with limited rest.
However, Dr Fu cautioned that researchers must first understand the underlying biological mechanisms before developing drugs.
She warned that altering sleep patterns without activating the protective pathways associated with FNSS could lead to serious long-term side-effects, including Alzheimer’s disease, Parkinson’s disease or cancer emerging after five to 20 years.
Beyond these rare mutations, sleep duration is estimated to be 30 per cent to 65 per cent heritable and influenced by hundreds of genomic regions.
A preprint study led by geneticist Isabelle Austin-Zimmerman at King’s College London analysed data from nearly 650,000 adults and identified around 244 genetic variants associated with sleep duration.
Although each common variant changes sleep duration by only about a minute, their combined effect accounts for roughly 20 minutes of variation in the average person.
Mental health: Resilience versus risk
Research into common genetic variants has revealed contrasting effects on health.
A study led by Dr Chiara Petrosellini, a clinical academic obstetrician and gynaecologist at University College London (UCL), examined 343 mothers with bipolar disorder.
Women with the highest genetic likelihood of being short sleepers had half the risk of developing postpartum psychosis and insomnia compared with those with the lowest likelihood.
Researchers suggested that these women might have developed greater tolerance to sleep disruption earlier in life, reducing the effects of sleep deprivation on their mood after childbirth.
However, broader population research by Austin-Zimmerman’s team found that genetic variants associated with shorter sleep were generally linked to higher risks of insomnia, fatigue, attention deficit hyperactivity disorder (ADHD), depressive symptoms and type 2 diabetes.
The findings suggest that a genetic predisposition to short sleep does not automatically protect people from related health risks.
The illusion of functioning on little sleep
Sleep experts warn that most people who claim to function well on very little sleep are likely experiencing hidden cognitive impairment.
A study co-authored by Hans van Dongen, a sleep scientist at Washington State University’s Sleep and Performance Research Center, found that healthy adults restricted to four or six hours in bed each night experienced steadily declining performance in cognitive tests.
Despite their worsening results, participants rated themselves as only “slightly” sleepy after two weeks.
Van Dongen explained that people can become increasingly impaired while growing less aware of their cognitive deficits. However, his separate research confirms that a small minority genuinely possess resilience to sleep deprivation.
Understanding genetic differences
Long-term research by Fu and Austin-Zimmerman aims to identify people who are genuinely resilient to short sleep and develop therapies that could help others build similar resilience.
For Bernard, discovering her FNSS mutation brought considerable relief. It dispelled her previous concerns that her short sleep resulted from an inability to relax or taking on too many responsibilities.
Knowing that her sleep pattern is genetically determined has allowed her to enjoy her productive early mornings and embrace her natural sleep rhythm.
