Insomnia is a common complaint in older adults. Whether this is a natural, normal part of getting older has been a subject of debate. Is this insomnia of the secondary type - caused by other illnesses or medications – or the primary type – with no connection to other maladies. This chicken-and-egg question of the relationship between declining sleep quality and development of chronic illness in older adults: Does low quality sleep contribute to other physical problems or do illnesses cause the low quality sleep?
The emerging consensus is that decline in sleep quality with age is not normal or inevitable. It is quite common, but increased rates of insomnia in old people are because of secondary insomnia, not primary insomnia. It just so happens that common, non-obvious degeneration of the neural system in older people causes circadian activity rhythms to become irregular, sleep to fragment, and daytime sleepiness to increase in severity and duration. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3199684/)
Chronic sleep difficulties affect older people more often than younger adults. The homoeostatic regulation of sleep changes as we age, although this is now thought to be due to illness, rather than a normal part of aging. Older adults typically have shallower sleep, and fragmentation is more common. Doctors prescribe sleeping aids to the elderly much more often than for young adults or kids.
It’s not just a subjective experience of insomnia. Polysomnographic measurements of physiological indicators have confirmed the reality of the decreased quality and quantity. Deep sleep, as a percentage of total sleep, decreases as people age, along with a decrease in growth hormone levels. During late life, REM sleep in a typical night declines about 10 minutes per decade. Wake time during the nocturnal period, a measure of sleep fragmentation, increases about 30 minutes per decade.
Factors that contribute to insomnia in seniors may include medical illnesses and medication use, both of which are more common in older adults. Some seniors also have too little physical activity and reduced exposure to bright light. The healthiest seniors who are the most physically active and the have the fewest health problems tend to experience the best sleep.
What percentage of seniors have insomnia? Nobody knows for sure. Even among younger people or the general population the prevalence of insomnia is not clear, because of variable definitions of insomnia among both surveyors and respondents. The National Institute on Aging's Established Populations for Epidemiologic Studies of the Elderly estimated 42% of community-dwelling seniors have insomnia, although seniors living in other situations probably have lower rates. That organization estimated the incidence (rate of onset) of insomnia at 5% per year.
There is also an age-related alteration in the neurobiology of circadian rhythms, although scientists haven’t figured it all out. As people age, the amplitude of the circadian rhythms decline. This may be due to changes in the brain from undiagnosed conditions. Very healthy elderly people do not seem to have this decline in circadian signals. However, this loss of circadian signal is common, and scientists have found even in aged animals that the suprachiasmatic nucleus uses less energy and produces less neuropeptides.
As people get older, they are more apt to experience secondary insomnia due to medical conditions, and to experience sleep disorders such as apnea, restless leg syndrome, and circadian rhythm disorders. Primary insomnia and insomnia due to psychiatric problems do not increase with age.
Sleep medication metabolism in the elderly differs from that in younger people because of the longer retention time in the body. A drug's half-life – the time it takes for the body to eliminate half the drug from the bloodstream – is higher in the elderly. This means sleep inertia due to residual sleeping pills is more likely in older people.
In general, older people are more prone to movement during sleep and sedative drugs increase the risk of falls. This is why doctors take into account a patient's age when selecting a sleeping aid. Benzodiazepine drugs are in particular problematic for the elderly. They increase the risk of falls, unsteady balance, and cognitive decline.
Insomnia affects a third of older Americans. Restless leg syndrome and sleep-disordered breathing/apnea are also more common in older people. Sleep-disordered breathing is particularly of interest because there is evidence that connects it with dementia and cognitive deficits in the elderly.
Free-running disorder is common in the elderly - people with this disorder are essentially unaffected (or underaffected) by zeitgebers.
Older people spend more time in bed than younger ones, but nighttime sleep is typically shallow and fragmented. Some of the sleep hygiene practices recommended for insomniacs are often ignored by older people. Retired people without the regular schedule of a job are more likely to engage in daytime napping, irregular arising time, and increased time in bed compared to employed people. These practices are not conducive to trying to beat insomnia.
Some common poor sleep habits are more prevalent in elderly populations – staying in bed all night even when not sleeping (leading to poor sleep efficiency) and daytime napping. This can be due to retirement or boredom. Good sleep practices can help.
Older people are smarter earlier in the day, and performance on mental tests falls as the day proceeds, even more than in young people. Mood is generally better early in the day. There’s a difference in the sexes. Men lose more of the deep sleep (stage 3) than women. Daytime sleepiness is more frequent in older men than in older women.
When it comes to insomnia young and middle-aged adults typically complain of difficulty falling asleep, seniors more often experience nocturnal awakening, early morning awakenings, and non-refreshing sleep.
Growth hormone, which is released in a pulse in the first period of slow-wave sleep, becomes scarce as people get old, and the amount of slow-wave sleep declines, too. In the body, the hormone somatostatin slows release of growth hormone. When elderly people are given shots of somatostatin, their sleep becomes more fragmented.
It used to be believed that the human circadian clock had a period of about 25.25 hours and that this period declined as people got older. This explained why teenagers had trouble waking up in the morning while seniors get sleepy early in the evening. However, circadian rhythm amplitude sometime stays strong in very healthy older people. Now scientists think that the intrinsic period of endogenous human circadian pacemaker is not significantly different between healthy old and young adults and is much closer to 24 hours. Deterioration in the suprachiasmatic nucleus may represent a pathologic rather than a normal change.
Another view is that older people tend to have a narrower window in the circadian cycle to get to sleep. They are literally more set in their ways. Young people can go to bed at a different time each night and move their sleep times around much more flexibility.
During late life, REM sleep declines gradually by about 10 minutes per decade. Sleep fragmentation, as measured by wake time, increases by 30 minutes per decade during late life.
Dutch scientists have found that elderly bodies are less capable of thermoregulation than younger ones, and give the effect of skin temperature on the ability to fall asleep and stay asleep, this may explain increased insomnia rates in seniors. (More on thermoregulation and sleep.)
It has been suggested that the desynchronization of the circadian cycle experienced to some extent by most old people contributes to upsets in thermoregulation and other physiological processes, including acceleration of tumor growth. Body temperature varies with sleep and waking: people wake up when the body temperature rises (and in prehistoric times before indoor heating and cooling, this coincided with the increase in the ambient temperature of the morning air). Declining body temperature at night coincides with bedtimes. If the circadian cycles of body temperature falls out of step with the clock, the person can be said to be experiencing circadian desynchronization. This is a common phenomenon among older people and partly explains sleep maintenance insomnia and excessive daytime sleepiness.
The prevailing hypothesis in sleep models is the two-process model in which sleep is a affected by circadian and homeostatic processes . The decline in sleep quality that goes along with getting old is thought to be due to alterations in both processes. Researchers at Cornell's Laboratory of Human Chronobiology found that the homeostatic process starts to go off-kilter before the circadian process as we age. They found this by studying people of different ages.
They also found that while young adults sleep longer than middle-aged and older adults, daytime napping is essentially unchanged as we age, in the absence of other life changes. One of those life changes could be retirement and the reason retired people seem to nap a lot isn’t that they are old; it’s that they are retired.
As people get older, their circadian cycle generally shifts backwards on the clock. Most teens naturally sleep late and go to bed late, but this shift disappears as the person gets into their 20s. The timing of the cycle is pretty stable throughout adulthood with a slow backward motion. However, past age 60 almost all people see a pronounced move backward. New genetic findings offer a partial explanation. The genes that regulate the circadian cycle change as we age. Elderly people experience a new internal body clock that makes them more proficient at cognitively demanding tasks in the morning than at night. Research was published in the Proceedings of the National Academy of Sciences.
When the U.S. government started the National Institute on Aging in the 1970s, sleep was a low priority among authorities who controlled medical research funding. In the past few decades the importance of sleep has been recognized, both as an important part of quality of life and as a contributor to and symptom of diseases.
Authors of the 2003 National Sleep Disorders Research Plan concede that most of the research on sleep is conducted on young adults and that there has not been enough scientific exploration of how age affects sleep. There isn’t widespread agreement on what is "normal" age-related changes in sleep patterns and therefore no consensus among physicians on whether any medical treatment is desirable.
Sleep fragmentation and arteriosclerosis (“hardening of the arteries”) are co-morbid. Middle-aged and older people with one are more likely to get the other. Both increase the risk of cognitive impairment.
While parasomnias are common in children, the problem at the other end of life is more often dyssomnia. In addition to insomnia, prevalence of apnea, restless leg syndrome, and circadian disorders increase with age. Narcolepsy incidence increases slightly, although most narcoleptics have it by age 30.
Parasomnias that are more common in older people include nocturnal leg cramps and REM sleep behavior disorder. Enuresis, although more common in young children, afflicts about 2% of the elderly.