Aging and sleep — do our sleep needs change over time?

As we age during adulthood, our sleep tends to change in a number of ways. These changes include structural transformations, for example in the timing, duration and pattern of our sleep, as well as specific variations in brain activity during certain sleep stages.

Researchers have shown that normal aging is linked to sleep impairments in otherwise healthy seniors. However, lifestyle changes, gender, poor health, illnesses and diseases common in old age also play a role in determining whether a person’s sleep will become disrupted in later life.

This article will consider how the aging process is related to sleep changes that occur throughout adulthood. An understanding of this multifaceted relationship informs the debate about whether our sleep need reduces as we age, which is also outlined in this article.

How does our sleep change as we age?

Over the course of our lifespan there are structural changes to our sleep, as well as specific changes to the quality and quantity of brain wave oscillations. In some instances, the specific changes to our sleep appear to occur independently of structural mechanisms.

The timing and duration of sleep changes as we age, with earlier bedtimes and rise times and shorter overall sleep durations becoming more common in older adults. There are also significant increases in sleep fragmentation amongst older adults, including a greater frequency of night wakings (which appears to plateau after the age of 60), decreased sleep efficiency, and more instances of fragile sleep, making us more prone to waking in response to external stimuli.

In older age our sleep also becomes lighter. The amount of deep non-rapid eye movement (NREM) sleep (also known as slow wave sleep) decreases and the proportion of light NREM sleep, specifically stages 1 and 2, increases.

These structural changes cause many older adults to experience more daytime sleepiness and increase the frequency of their daytime naps. Up to 50% of older adults report subjectively poor sleep quality. However, self-reported sleep quality may not be a helpful measure of sleep changes in older adults as sleep complaints are often linked to poor health rather than aging, while many healthy elderly people regard their poor sleep as an inevitable part of aging.

Significant reductions in slow wave brain activity occur in middle age and become particularly prominent in old age. Studies have found that the amplitude, number and average frequency of slow wave oscillations reduce as we age. Even when older adults maintain the same total amount of NREM sleep, there are still significant differences in the density and amplitude of slow waves within those sleep stages.

Slow wave activity is closely linked to the homeostatic drive to sleep following periods of continued wakefulness. The longer we remain awake (i.e. during the day), the greater the pressure to sleep and the greater the amount of slow wave activity when we sleep. In young adults, slow wave activity peaks in the first NREM cycle of the night and then declines across subsequent sleep cycles as the pressure to sleep dissipates.

This process plays a role in regulating the sleep-wake cycle and the effect appears to alter over the course of adulthood. In older adults, the pressure to sleep does not dissipate as dramatically and the amount of slow wave sleep does not correspond as much with the amount of prior wakefulness.

The homeostatic drive to sleep is partly regulated by extracellular adenosine, which accumulates while we are awake for an extended period. There is evidence to suggest that older adults actually have higher adenosine levels. It may be the case that the loss of adenosine receptors or age-related changes in the glial function inhibits the ability of older adults to respond to increased levels of extracellular adenosine, producing a lower homeostatic sleep response.

The time spent in stage 2 NREM sleep does not appreciably vary with age, but the sleep spindles — bursts of neural activity that support cognitive functioning — which occur during this stage of sleep deteriorate in terms of their number, duration, peak and amplitude.

This shows that specific aspects of sleep — notably, slow wave brain activity and sleep spindles — can change with age in ways that are distinct from broader changes in sleep structure. This will be an important point to remember when we go onto discuss the debate about aging and sleep need.

Other specific changes which may contribute to poor sleep in old age include reductions in the number of neurons responsible for initiating and maintaining sleep and sleep-wake regulation, the thinning of gray matter in the brain, the decline in certain sleep-related hormones and deterioration of aspects of the circadian rhythm.

Most of the changes outlined above occur over the course of middle age and either stop or become slower after the age of 60. Men generally suffer far greater disruption to slow wave sleep as they age compared to women, but women are more likely to complain of poor sleep. The reasons for these gender disparities remain unclear.

“Older adults do not require as much sleep as younger adults” — the evidence

One school of thought argues that our sleep need simply declines with age so that older adults require less sleep than younger adults. Proponents of this view highlight a number of different phenomena to support their claim.

Firstly, when offered very long, enforced periods of sleep opportunity, older adults have been shown to sleep significantly less than younger adults. This suggests that older adults have a reduced sleep need.

Secondly, studies have shown that older adults demonstrate a smaller rebound in slow wave sleep time and slow wave activity following a period of sleep deprivation or slow wave sleep suppression. This suggests that older adults experience a lower build-up of homeostatic sleep pressure, which could reflect a natural decline in sleep need.

Thirdly, older adults suffer less objective and subjective sleepiness following slow wave sleep deprivation (and when fully rested) compared to younger adults. Older adults also show less impairment on sleep-sensitive vigilance tasks under sleep deprivation conditions. This suggests that older adults don’t need as much sleep to continue functioning at the same levels during the day.

Why may this argument be problematic?

Another school of thought argues that we have the same sleep need as we age but we are less capable of meeting that need. This could be a better explanation for why older adults are found to sleep considerably less than younger adults when given lots of opportunity to sleep.

Levels of extracellular adenosine, a major marker of homeostatic sleep drive, actually increase in many sleep regulatory centers of the brain as we age. This indicates that older adults have a higher sleep need.

The lower build-up of sleep pressure in older adults may not reflect a lower sleep need. Instead, it may reflect an impaired sensitivity to a still present, or increased, sleep drive. This is because adenosine receptor loss and neuronal loss in sleep regulatory centers inhibits the ability of older adults to translate increased sleep need into increased sleep pressure.

Reports of less subjective sleepiness amongst older adults may not provide a reliable indication of the sleep quality actually experienced by older adults because we have the ability to normalise the effect of chronic sleep restriction. The apparent lack of impact that sleep deprivation has on the performance of older people in vigilance tasks may simply reflect a lower baseline as older adults often perform significantly worse under well rested conditions than younger adults.

Older adults perform significantly worse on sleep-dependent cognitive functions, such as learning and long-term memory consolidation. This is due to the degree of impairment to NREM sleep, not just the aging process, as older adults of the same age perform differently. The deterioration of sleep in older adults has cognitive consequences, indicating that older adults are less capable of generating the sleep they need to maintain certain cognitive functions at optimal levels.

The argument that the aging process lowers our sleep need also neglects the fact that poor sleep in seniors can be attributed to many reasons, including the pain and discomfort associated with illnesses, the side effects of medications and lifestyle changes.

What does this mean in practice?

The current evidence appears to support the hypothesis that older adults do not have a reduced sleep need, but rather, an impaired ability to register and/or meet that sleep need. This does not mean that older adults need to sleep more. Instead, it means that sleep quality and the capacity to achieve consolidated NREM sleep may become deficient in advancing age.

The National Sleep Foundation guidelines recommend 7–8 hours of sleep each night for those over the age of 65. Experts also advise improving sleep hygiene and implementing safety measures such as keeping a phone and a light switch within reaching distance as you sleep, and eradicating trip hazards as poor sleep can increase the risk of falls and accidents.

Sleep has been receiving more attention in geriatric research due to increasing evidence that links poor sleep in older adults to adverse health outcomes, especially cognitive decline. Better self-reported sleep has been linked to better health outcomes, particularly in mental, cognitive and physical health. There are potential interventions that could promote restorative sleep and daytime wellbeing in the elderly.