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Part 1
Understanding Age Related Sleep Disorders
of various tissues only occurring
during certain stages of sleep.
Weymouth - It is commonly understood that the quality Generally, people cycle through
of our sleep gets worse as we age, but it does not have to progressively deeper stages of
be that way - poor sleep is not a normal part of aging. non-REM sleep for about 90Most of the ways in which sleep deteriorates over time is 120 minutes before the first
related to the medical illnesses that many people acquire REM period, after which the
as they age, side effects of the medications used to treat cycle repeats itself with Stage
those conditions, environmental factors that are hostile to 3 sleep gradually disappearing
sleep, and bad habits. Before diving into those topics in and REM periods becoming
later articles, this article will briefly review the structure and progressively longer (Figure 1).
Matthew Weiss, M.D.
function of normal sleep and how it evolves as we age.
The most fundamental changes in sleep that happen with
There are two categories of sleep, REM (Rapid Eye Movement) healthy aging relate to the relative amounts of each stage of
sleep and non-REM sleep. A common misconception is that sleep that occur each night. Stage 3, the deepest and most
REM sleep is “deeper” than non-REM sleep. In reality, the restorative stage of sleep is most abundant in children.
two types of sleep are entirely different. REM sleep, current
research suggests, is important for learning and memory.
By Matthew Weiss
Dreams occur during REM sleep, many of which involve
rehearsing new skills or organizing new learning so it can
be recalled later, but every muscle in the body is paralyzed,
except the diaphragm, so we continue to breathe, and the
muscles around the eyes (hence “rapid eye movement”).
The muscle paralysis is useful, or we would run away from
the dinosaur chasing us or strike out at an adversary in our
dream, and indeed people with a condition called REM
Behavior Disorder do exactly these sorts of things. During
REM sleep, heart rate, breathing rate, and blood pressure
skyrocket, possibly in response to the content of the dream.
Figure 1: A hypnogram that charts the progression of
sleep stages and cycles during a normal night of sleep.
Non-REM sleep has three stages, numbered 1, 2, and Note that this figure is somewhat outdated because
3 (there used to be a Stage 4, but this stage was recently it includes Stage 4 sleep, which is now combined into
eliminated by a panel of scientific experts), with Stage 1 Stage 3. (Source: Wikipedia).
representing the shallowest stage of non-REM sleep and
Stage 3 the deepest and most restorative. These stages are Men see a decline in Stage 3 sleep with age, from about
identified by measuring brain waves, and the deeper stages 11% of total sleep time in their 30s to about 5% in their
are characterized by an increase in slow brain activity.
70s. Women, on the other hand, see a slight increase from
The muscles are not paralyzed during non-REM sleep, but 14% in their 30s to 17% in their 70s.
generally this type of sleep is more restful and restorative for The decrease in Stage 3 sleep in men is accompanied by a
the body, with the secretion of certain growth hormones and parallel increase in Stage 1 and Stage 2 sleep, suggesting that
other processes involved in growth, repair, and regeneration even healthy older men sleep less deeply than younger men.
Reprinted By Permission
The overall amount of REM sleep, which generally takes
up 18-20% of the night in adults, remains stable from
our mid-30s onward. Changes beyond the ones discussed
here relate to acquired diseases and other factors that were
mentioned at the beginning of this discussion.
Sleep is an important and complicated biological
phenomenon, but it does not occur just anytime. We only
sleep when we feel sleepy, and normally we only feel sleepy Figure 2: The two-process model of sleep regulation.
at a certain time each night, assuming we slept normally Process C is related to the circadian rhythm and Process
the night before. The explanation for when and why we feel S refers to “homeostatic” sleep drive and time of day is
sleepy has been called the “two process model” (Figure 2) in a 24-hour format (23 = 11 PM). (Adapted from Borbély
because there are two independent processes that interact and Achermann, 1992).
to determine when we feel sleepy and when we can sleep.
happens to be the only hormone you can buy over the counter.
Process C (Circadian) refers to a rhythmic waxing and The usual peak of melatonin, which signals the brain that it is
waning of body temperature and certain hormones that lead time to go to sleep, happens two hours prior to bedtime (so if
to wakefulness and sleepiness at certain times of day. Many you’re taking melatonin at bedtime, with few exceptions, you’re
people believe that they feel sleepy after lunch because a taking it wrong!) and is opposed by light, particularly blue light.
significant amount of blood rushes to their stomach and Since the lens of the eye gets increasingly more yellow with age,
away from their brain, or that something in what they ate, a greater amount of blue light is blocked, which is one factor
that leads to a weakening of peak melatonin secretion.
such as tryptophan in turkey, made them feel sleepy.
Looking at Line C in Figure 2, it is easy to see that the
biological drive to stay awake begins to decline around 2-4
PM, which is when people encounter the “mid-afternoon
dip” and some cultures schedule a siesta, or nap. Notice a
second dip at 2-4 AM, a time that has been associated with
an increase in auto accidents and other causes of injury and
death related to a drop in attention and wakefulness for
people who are awake at this time.
Bright light in the evening, as well as exercise and food just
before bed or in the middle of the night, can suppress melatonin
and interfere with the ability to fall asleep and stay asleep. An
irregular sleep schedule can also interfere with the normal
circadian ebb and flow of melatonin and produce a feeling like
jet lag, which makes sense because travel across time zones that
results in light exposure at a different time than we are used to
is exactly what causes jet lag.
The second process, process S (sleep) is related to homeostatic
sleep drive, or what many people refer to as “sleep debt.” In
short, you begin racking up sleep debt the instant you wake
up (7 AM in Figure 2 on Line S) and this sleep debt peaks
approximately 16 hours later, when there is a parallel low
point in the circadian wakefulness drive (Process C) and a
peak in homeostatic sleep drive (Process S) that combine to
allow a person to fall asleep. Once asleep, the sleep debt is
paid off in the form of Stage 3 sleep, which is why this stage
of sleep is seen mostly at the beginning of the night and
gradually disappears, and assuming an adequate amount
and quality of sleep, is fully paid off by 7 AM the next day,
coinciding with the next rise in Process C.
Now that we have a basic understanding of how sleep
functions, what the building blocks of a good night’s sleep
are, and how they fit together, next month’s article will
begin to look at how sleep can be compromised as we age.
Stay tuned, sleep tight, and don’t let the bedbugs bite.
About The Author
Matthew Weiss, M.D., F.C.C.P. is board-certified in internal medicine, pulmonary disease, critical care medicine, and
sleep medicine. Dr. Weiss is medical director of the Physician
Diagnostics Sleep Program at Harbor Medical Associates,
where he diagnoses and treats the full range of sleep disorders.
For information on the Physician Diagnostics Sleep Program,
The circadian rhythm is controlled by a hormone called or to arrange a consultation call (781) 952-1460 or visit
melatonin. You have probably heard of melatonin, which www.harbormedical.com.
Reprinted By Permission
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