Cortisol
- The Anti-Sleep Hormone
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. Our postural muscles, which have worked
all day to keep us upright and moving about, now relax. 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 oversecretion 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 excite, or hyperaroused.
When we're chronically hyperaroused, we can't sleep, and the sleep
we do get is not as restful.
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