We all know that sleep is important for our mood, productivity and general health. But what you might not realise is how serious the health implications of sleeplessness can be, particularly for older people and teenagers.
Researchers at the Brigham and Women’s Hospital in Massachusetts found that a lack of sleep – defined as five hours’ sleep or less a night – can double an individual’s risk of dementia. The study, conducted among 2,812 adults aged 65 and over, also found that those getting less than six hours’ sleep were at greater risk of memory loss and difficulties with language and problem-solving compared with people sleeping for at least seven hours a night.
The respondents were asked a range of questions, covering aspects including quality of sleep, frequency of awakenings, incidence of snoring and regularity of napping. They then examined the relationships between these characteristics and outcomes, including incident dementia and all-cause mortality.
Routinely taking 30 minutes or longer to fall asleep was associated with a 45% greater risk of dementia. The researchers also found associations between difficulty in maintaining alertness, routine napping, poor-quality sleep or sleeping no more than six hours a night with an increased risk of premature death.
We all accept that insufficient sleep is not good for our brain function – we know that we may not perform well if we don’t sleep well
“Our results showed that, among all the characteristics, short sleep duration was the strongest predictor of incident dementia. Those sleeping for no more than six hours a night were at an elevated risk,” says researcher Dr Rebecca Robbins, instructor in medicine at Harvard Medical School and co-author of Sleep for Success! Everything you must know about sleep but are too tired to ask.
Sleep and mental health
Sleep experts at the University of South Australia, Adelaide, believe that both parents and medical practitioners need to improve their awareness of the relationship between sleep and mental health in teenagers.
Dr Alex Agostini, a lecturer at the university, observes that sleep is especially important for people in this age group because they are going through a range of potentially stressful physical and developmental changes.
A teenager regularly getting less than six hours’ sleep a night is twice as likely as average to engage in risky behaviour such as dangerous driving and drug abuse, according to the researchers.
Attributing cause
While studies show clear correlations between a lack of sleep and health problems, scientists acknowledge that establishing causal links is a harder task. Professor Derk-Jan Dijk is director of the University of Surrey’s sleep research centre and a former associate neuroscientist at the Brigham and Women’s Hospital. He notes that attributing causes for dementia, for instance, is complex, not least because of the possibility of reverse causality.
“If there is something wrong with a person’s brain, it could affect their sleep,” he explains. “But yes, extreme sleep patterns and disorders are associated with adverse health outcomes, including dementia.”
Tim Beanland, head of knowledge management at the Alzheimer’s Society, also observes that the relationship between sleep deprivation and dementia is complex. Different types of dementia are associated with different sleep problems, he adds.
“Researchers are not yet sure which way the interaction goes – whether poor sleep causes or exacerbates dementia, or if dementia leads to poor sleep,” Beanland says. “Some researchers believe that both of these theories could be true and the relationship could be circular. On top of this, the mechanisms that underlie these interactions are unclear. More research is needed, particularly studies that observe large groups of affected people for long periods.”
Recent research suggests that the glymphatic system – a network of vessels that clears waste chemicals from the central nervous system, mostly during sleep – may be disrupted by, and contribute to, some diseases of the brain.
Disturbed sleep is also a risk factor for numerous other health issues. Disorders such as sleep apnoea, when breathing repeatedly stops, may increase the risk of cognitive decline, while the impact of both very short and long sleep duration have been reported for many other health outcomes.
How to get enough sleep
Simply going to bed earlier may not be the answer to getting enough sleep, according to Dijk. He believes that the most effective solution is to find the “sweet spot” – the best time to go to bed for uninterrupted, high-quality sleep.
“We all accept that insufficient sleep is not good for our brain function – we know that we may not perform well if we don’t sleep well,” he says. “But there’s no better way to ruin your sleep than by spending too much time in bed. For example, people who go to bed too early are likely to have their sleep interrupted.”
Daytime napping, while not always a bad thing, does not make up for a poor night’s sleep, says Dijk, who adds: “There are certainly healthy nappers, but it’s a bit of a misrepresentation to say that napping is a good thing. Healthy older people should not be sleeping during the day. If you’re doing that, you’re not getting enough sleep at night, or there’s another health problem.”
If napping is not the answer, could sleeping tablets be? Referring to another study run by the Brigham and Women’s Hospital team, Robbins suggests that the answer is no. In an analysis of medication usage among older people in the US, this research found that 15% of the sample routinely consumed sleep medication. This usage was associated with incident dementia across the follow-up interval.
While people might be tempted to use weekends to catch up on their sleep, getting a regular seven-plus hours’ worth is more important, particularly for teenagers, according to Agostini.
“There are so many reasons why it is healthier to minimise sleep loss by regularly going to bed a little earlier throughout the week than it is by trying to make it up over the weekend,” she says. “I don’t recommend a delay in wake times of more than an hour on Saturday and Sunday mornings.”
