Compared
with good sleepers, people with insomnia secrete more cortisol in the
evening before bedtime and in the first half of their sleep; they
also have more fast brain-wave activity in non-rapid eye movement
(NREM) sleep, both indicators of arousal. Stress is the principal
cause of the insomnia that plagues so many millions of Americans.
How
does stress cause insomnia? To understand that, we must first know a
little bit about the physical processes that occur when we fall
asleep. Falling asleep is a natural process that involves a distinct
sequence of events in the body. As we approach sleep, there is a
gradual lowering of metabolism. Our heart rate slows and our blood
pressure declines. Our breathing becomes more regular, and we consume
less oxygen. At the same time, there are changes in the processing
activity of the brain. The activity of neurons in the cerebral cortex
becomes first slower, and then more synchronized, indicating a shift
away from the complex, activated patterns of waking consciousness and
toward a homogenous, deactivated state. As a result, we cease to
process the sensory messages coming in from the outside world, and we
slip into quiet sleep.
The
adrenal hormone cortisol is a trigger of the stress response. That's
not cortisol's only job, however. In addition to the sharp transitory
peaks of cortisol secretion that characterize the stress response,
there is also a daily, cyclical rise and fall of cortisol levels that
govern our level of wakefulness throughout the day and night.
Cortisol is excitatory; it arouses us and wakes us up. Blood levels
of cortisol have been shown to increase between 50 and 160 percent
within thirty minutes of waking; that produces the powerful jolt of
arousal needed to wake us up and get us moving in the morning. Then,
cortisol levels should decline as the day wears on and reach their
lowest point in the evening, allowing us to rest, relax, and sleep.
But,
as we know, cortisol levels can also be affected by the conditions of
our daily existence. Dangerous, demanding, or threatening
events--stressors--cause us to temporarily secrete higher levels of
cortisol. That's a good thing, because we need to be aroused in order
to answer the challenges that arise in the course of our lives. But
when, as a result of prolonged or unremitting stress, whether real or
perceived, our cortisol levels get stuck at a chronically higher
level, that's bad news for our bodies and minds, and especially bad
news for our ability to sleep and rest. Chronic over-secretion of
cortisol leaves us chronically hyperaroused. Numerous studies
indicate that insomnia is accompanied by excessive activation of the
stress-response system not only during waking hours but during sleep
as well. Furthermore, chronically elevated levels of cortisol and its
precursor, adrenocorticotropic hormone (ACTH), can make sleep
shallow, fragmented, and unrestful; delay the onset of sleep; and
produce more frequent nocturnal awakenings.
Stress
is the principal cause of insomnia. Stress hormones are excitatory.
When stress becomes chronic, we become chronically excited, or
hyperaroused. When we're chronically hyperaroused, we can't sleep,
and the sleep we do get is not as restful.
