The truth about whether you need less sleep as you get older

By Claudia Hammond

The older we get the fewer hours we need to sleep, seems to be the accepted wisdom. But there might be other reasons for waking up earlier in the morning.

It’s common for older people to say they have trouble sleeping. As many as half report some kind of sleep disturbance, with between a quarter to a third experiencing insomnia.  

There seem to be two main difficulties: falling asleep at the start of the night and then waking up too early in the morning – yet finding it impossible to get back to sleep. In some cases, the discomfort caused by a medical condition exacerbates sleep difficulties, but many find that even without the disturbance of physical symptoms, sleep still eludes them for at least part of the night.

A lack of sleep can have a long-term impact on the immune system and on many other aspects of health, includingwellbeing, as well as leading to daytime sleepiness and an increased risk of accidents. But maybe people simply don’t need as much sleep when they’re older and needn’t worry about it.

It is harder than it sounds to establish how much sleep people of different ages need. You can, of course, measure how many hours of sleep people actually get and if you do this you find that on average older people sleep for a shorter time than their younger friends, but that only tells you that they get less sleep, not that they need less sleep.

Sometimes people will say that the reason older people can’t sleep at night is they’ve spent part of the day napping. But, others argue that feeling excessively sleepy during the daytime should not be accepted as an inevitable aspect of ageing.

Insomnia in the retired is not always taken seriously by doctors. In one study, 69% of older people reported a sleep problem, but in 81% of cases the problem was not noted on the patient’s chart.

So if we imagine for a moment that older people do need the same amount of sleep, why then do they sleep for fewer hours? One hypothesis is that the aging process disrupts their circadian rhythms, causing them to wake earlier than they should. Studies have demonstrated the clock does seem to shift, leading people to wake earlier in the morning and go to bedearlier at night. They might still need the sleep, but they can’t get it and when they do fall into a slumber, the quality of sleep is not as good as when they were younger.

In a new study from Russia, 130 people went to a laboratory one morning and then stayed there all day and overnight. Staff kept them awake for the entire time, regularly asking them to assess how sleepy they felt. These feelings of sleepiness vary throughout the day and night and in sleep deprivation experiments such as this, they are taken to reflect processes related to the body clock such as changes in body temperature at different times of day and the release of the hormone melatonin in the evening.

The slow-wave activity in the volunteers’ brains was also measured several times during the day and night. Then all this data was analysed in relation to a sleep diary the people had kept for the previous week, in order to see how the pattern of sleepiness and slow brainwaves varied according to propensity to be morning or evening types. They found that, once again, the older people felt sleepy at different times from the younger people and had different timings of slow-wave activity in the brain.

The study’s author, Arcady Putilov, suggests that two mechanisms might be responsible for the decrease in sleep time. He believes that in middle age the processes underlying the oscillations of slow-wave sleep weaken, making it harder to stay asleep, and on top of that, in older age the stronger circadian rhythms weaken because changes in body temperature and the release of the hormone melatonin weaken.

Support for a role for the impact of circadian rhythms on the disruption of sleep in older people, comes from brand new data obtained using a smartphone app called Entrain, developed by the researchers at the University of Michigan, Ann Arbor, to help people adjust their light levels at different times of day in the hope of combatting jet lag.

Users of the app are asked about their typical sleep patterns and canchoose whether to share that data the researchers. Five thousand people from around the world did, which has provided a snapshot of global sleeping habits of people of different ages. Among the young people there was a range of early risers and night owls, but the older group was more homogenous.

Most woke early and went to bed relatively early. In this study it was the men in their 40s who seemed to get the least sleep, which is unusual. But the finding that older people sleep at more specific times suggests that there is a narrower range of times in which people past retirement age are able to get to sleep and stay asleep.

So changes in the body clock stop older people getting to sleep and keep older people awake, maybe, then, it is a myth that they need less sleep. It’s simply that they have a narrower window in which to sleep. Perhaps the daytime napping isn’t preventing sleep at night. Instead the lack of sleep in the night is causing sleepiness in the daytime, hence the need for a nap to make up for the lost sleep.

But the debate doesn’t end there. In a 2008 study, a study conducted at Brigham Women’s Hospital in the US, gave people the chance to sleep for 16 hours a day for several days. The 60-to-72-year-olds slept for an average of 7.5 hours each day, while the 18-to-32-years-olds managed almost nine hours. You could interpret this as meaning that they needed more sleep than the older people, but there is also the possibility that they were more tired out with a greater sleep debt in the first place because they’d been going to bed late. This study doesn’t rule out the idea that the body clocks of the older people were preventing them sleeping during the day, even if they needed it. But the next study, conducted by some of the same researchers, this time at the University of Surrey, added an extra twist.

This time people were asked to try to nap at various times of day. Once again the older adults found it harder, implying that either their body clocks were keeping them awake or they hadn’t built up as much of a sleep debt as the young people. So this time the technicians made sure they were lacking in sleep. They monitored their brain activity all night and every time they detected slow-wave activity, they blasted the room with a noise, to disturb them. The followed day, tired out, the older people found it just as easy to snooze as the young people. So this suggests that when they really need the sleep they can get it and that, just maybe, the rest of the time they’re not sleep-deprived. 

After examining the findings of 320 studies an expert panel convened by the National Sleep Foundation in the US recommends seven-to-nine-hours sleep a night for adults up to the age of 64 and seven-to-eight hours for the over 65s.

Yet the idea of changes in the processes underlying circadian rhythms as we age, also seems compelling. So this is one where it’s not yet possible to say whether it’s a myth that older people need less sleep. What we do know is that trying to sleep on long, lonely dark mornings, and finding yourself awake, but unrefreshed, is miserable and should be taken seriously.

A Cochrane review of cognitive behavioural interventions for sleep problems in adults over the age of 60 looked at the very best trials and found that in some cases it can be effective and is worth consideration by doctors as an alternative to sleeping pills.

/By BBC/