Time and time again, adequate sleep has been shown to be critical to daily functioning and long-term health. Sleep serves numerous roles: recovering energy for the brain, clearing waste products, and forming memories.
Prior studies have clearly linked shortened sleep times to heart disease, obesity, reduced cognitive performance, worsened mood, and even a shorter life. There is now new research that suggests that lack of a certain type of sleep (the dream stage of sleep) may be related to an earlier death in middle-aged and older people.
Normal sleep is broken down into two sleep types: rapid eye movement (REM) and non-rapid eye movement (NREM). NREM is further classified by depth of sleep; N1 and N2 are lighter sleep stages, and N3 is deep sleep, which is most restorative. (REM is the stage where vivid dreaming occurs.)
Brainwave activity during this time appears similar to the brain’s activity while awake. REM periods generally occur every 90 minutes, and are longest during the second half of the night. REM sleep normally makes up 20% to 25% of sleep time.
Sleep time and sleep stages naturally change as we age. Total sleep time decreases by 10 minutes every decade until age 60, when it stops decreasing. Time in N3 sleep, the deepest sleep stage, also shortens with age; time in N1 and N2 tends to increase.
As a result, people wake more easily from sleep as they age. The percentage of REM sleep also naturally decreases; thus, reduced time spent in REM may be a marker of aging.
The circadian rhythm is a 24-hour internal clock that governs numerous body functions including body temperature, release of hormones, and sleep time. The internal clock “advances” with age, so older adults tend to fall asleep earlier and wake earlier.
Adapting to jet lag and shift work becomes more difficult. Daytime napping also increases as the strength of the circadian rhythm and the drive to sleep at night decrease.
Studies have also shown that older adults who are healthy may not perceive problems with sleep when it is actually impaired, or may assume that certain disruptions are part of aging when they have treatable conditions.
In the short term, sleep deprivation increases cortisol levels, causes increased blood pressure, decreases glucose tolerance, and increases the activity of the body’s fight-or-flight system, all of which are linked to increased risk of diabetes, heart attacks, and strokes.
Daytime cognitive performance is also reduced, resulting in more accidents. Twenty-four hours of sustained wakefulness impairs driving ability to the same degree as a blood alcohol concentration of 0.10%, which is above the legal limit.
In the long term, both short and long sleep (less than five hours or more than nine hours) have been associated with earlier death. People who sleep less than four hours dramatically increase their risk of dying early, possibly through heart disease, diabetes, high blood pressure, chronic stress, lower immunity, and overall more rapid aging.
We know that short sleep is associated with increased mortality, but until now it has been unclear if shorter sleep in a particular sleep stage makes a difference in the health risks associated with sleep deprivation.
A new study published in JAMA Neurology looked at the relationship between REM sleep and earlier death in two large study groups, one consisting of 2,675 older men and the other of 1,386 middle-aged men and women. They followed both groups over time and looked at the relationship between sleep stages and causes of death.
Both groups showed increased mortality rates related to a decrease in REM sleep, with a 13% higher mortality rate for every 5% reduction in REM sleep. REM sleep was the most important sleep stage for predicting survival.
This study showed an association between reduced REM and increased mortality, but it did not demonstrate the cause of the association. REM deprivation could independently contribute to the development of numerous other diseases.
The results apply more clearly to older adults, given that the age groups studied averaged in the 50s and 70s. Short REM may also be a marker of a sick or aging brain; less REM sleep has already been tied to a greater risk of dementia. Overall, ensuring adequate REM sleep is important to protecting your long-term health.
Getting better sleep in middle age and beyond
Maintaining good sleep should remain a priority throughout your life. Everyone can make healthy choices to maximize restorative sleep. Dr. Suzanne Bertisch has written previously about recommendations for improving sleep hygiene, and even more suggestions are available in the Harvard Health Publishing Special Health Report Improving Sleep: Getting a Good Night’s Rest.
Some fundamental steps to improve your sleep and health include:
Get at least seven hours of sleep each night. If you still feel tired, sleep a little more; some people need eight or nine hours of sleep to feel rested.
Keep a consistent bedtime and wake time. This will make falling asleep easier, and will keep your circadian rhythm aligned with your sleep and wake time.
Try to sleep when your body naturally wants to fall asleep and wake up. This can differ from sleep and wake times required for work schedules, which also has negative consequences. A sleep doctor can help you realign your circadian clock with your schedule.
Depression or other mood disorders can cause disrupted sleep. Talk to your doctor if you are feeling low, no longer enjoy your hobbies, or are struggling with anxiety or sadness.
If you can’t fall asleep, stay asleep, or feel sleepy all the time, you may need evaluation from a doctor for a sleep disorder such as sleep apnea or insomnia. Treating these disorders can make a major difference in overall sleep quality and health.
From Harvard Medical School