Sleep Debt: The Hidden Costs

Everyone has a sleep bank. Each night your accounts get credited with 7-8 hours of the physical and mental benefits of sleep and each day the accounts pay out those benefits in the form of emotional, intellectual and physical energy. Just like in any bank account, withdrawals can’t exceed deposits without incurring debt. Sleep debt, though, is easy to ignore because physical activity keeps alertness high. As long as you move around instead of reading or watching TV, you won’t nod off and you can keep thinking that 5 or 6 hours of sleep a night meets your needs. But covering the debt with activity is like keeping a bank balance out of the red by borrowing money and paying interest. Sleep debt exacts a toll on the body that goes beyond depressed mood, irritability and lack of ability to concentrate and learn, not to mention the potential for causing motor vehicle accidents.

The biological clock

As sleep debt mounts, the body’s biologic clock goes awry. This clock, located deep in the brain, controls circadian rhythms – regular ups and downs in behavior, body temperature, appetite, hormone production, alerting mechanisms, and the urge to sleep. When the clock malfunctions chronically, the results show up in the form of weight gain, high blood pressure, diabetes and diminished immunity to infection.

Setting the clock

Regular periods of darkness are required to set the brain’s internal clock to keep the body in synch with the 24-hour day set by the sun. Sleep researchers have shown that, when living in a research setting where there are no external clues about time of day or night, subjects’ internal clocks actually work on a 25-hour cycle. Normal peaks of sleepiness and alertness work themselves into the wrong time of the  24-hour day and night outside the sleep lab, producing weeks of daytime sleepiness and nighttime insomnia in the research subjects. Over time, the peaks cycle back into synchrony with day and night producing several weeks of normal daytime alertness and nighttime sleepiness.

Laboratory settings may exaggerate these patterns, but most people know that during some weeks they simply perform better during the day and sleep better at night  than during other weeks, indicating that in the modern, artificially lit world, the 24-hour day is more like a 24-25 hour day as far as the body’s natural rhythms are concerned. This clock drift is very sometimes very evident. Cyclical insomnia and daytime sleepiness are in common in blind people, in people at very high latitudes where the summer sun circles the sky for almost 24 hours, and in shift workers who are up all night in brightly lit environments. These problems, while distressing, respond to maintaining regular sleeping schedules and closing out all light during sleep periods, which resets the clock.

Why the clock matters

The internal clock is easily disrupted by one or two day episodes of sleep deprivation that people experience for reasons as varied as extra work loads, exams, brief periods of emotional upheaval, or any of the other myriad problems that keep people awake, but studies have repeatedly demonstrated that a few days of “catching up” on sleep restore the body to normal rhythms, contributing to a widely held impression that sleep deprivation, while responsible for serious accidents, doesn’t cause real health problems.
However, bigger problems do come from disturbing circadian rhythms more chronically. In recent years research attention has shifted from short term sleep deprivation to the chronic, partial sleep deprivation that is so common in our modern society, where nodding off during monotonous and sedentary activities like reading or watching TV are almost expected. Many people think they need no more than 5-7 hours of sleep at night, but while a few truly short sleepers exist, most people require around 8 hours of sleep each night to achieve maximal alertness throughout the day. Chronically shortchanging sleep by even an hour a day changes the timing and levels of multiple hormones, causing other metabolic changes and weakening the immune system.

Lack of sleep wreaks havoc on hormones

One of the first hormonal changes produced by chronic short sleep involves cortisol, the stress hormone produced by the adrenal gland. Normally cortisol levels decline during late evening hours, but without enough sleep, production continues unabated, Cortisol then begins to contribute to immune stress and to insulin resistance, which leads to diabetes and fat deposition. A second contributor to insulin resistance is a change in growth hormone secretion from one large burst during sleep to two, smaller bursts before and after sleep. A third change comes from failure of the pituitary gland to produce its normal night-time rise in thyroid stimulating hormone, the stimulus for the thyroid gland to produce more thyroid hormone. All of these changes are consistent with the fact that as little as one week of 4 hour sleeping nights can convert healthy young people to a pre-diabetic state. Observational studies do show higher rates of diabetes in chronically sleep-deprived women.

Lack of sleep and obesity

If these hormone changes are not enough to convince a short sleeper to turn out the lights earlier, studies on the appetite influencing hormones leptin and ghrelin, produced by fat tissue and the stomach respectively, might help. Leptin, which signals when to stop eating, diminishes markedly after 6 days of four- hour sleeping nights, despite no change in caloric intake. Ghrelin, which stimulates appetite, particularly for high carbohydrate foods, goes up when sleep is short.

Sleep debt is all around you

    All of these hormonal factors are significant in society where people lead overscheduled lives in stimulating, loud and bright environments without regard to natural day and night. We do not need sleep studies to tell us that we are in an age of significant sleep debt – just count the number of people, including children, asleep on planes and buses, over books and newspapers, and on couches in front of TVs. If you fall asleep regularly under these circumstances, you are in chronic sleep debt. Given the increase in obesity and diabetes over the last few decades, sleep is another potential therapeutic avenue – a fruitful and inexpensive area of health over which we have considerable control.

Managing the sleep budget: factors under your control

1. Take the television out of the bedroom.
2.Darken the room completely, or wear a comfortable, opaque eye mask.
3. If noise is a problem were soft ear plugs.
4. Keep the temperature low at night and invest in a comfortable mattress that does not move.

1. Keep the biologic clock in sync with the sun by getting outside regularly.
2. Get regular exercise like walking, but avoid exercise in the last 3-4 hours before bedtime.
3. Keep naps short – 45 minutes or so – and confined to early afternoon hours.
4. Avoid heavy meals and alcohol in the last 4 hours before sleep.
5. Aim for the same bedtime every night, well before midnight, and develop a quiet bedtime ritual

Internal factors
1. Empty your bladder right before getting in bed.
2. Seek medical treatment for heartburn if causes frequent awakening. Ditto for urination.
3. Evaluation for sleep apnea is a must for someone who snores and suffers from daytime sleepiness.
4. Treatment of arthritis with exercise, physical therapy and medications, if necessary.
5. Try to get weight down to normal: sleep apnea, heartburn, and arthritis pain all benefit

The Problem with Stress: No Fighting or Fleeing

…grant me the serenity
to accept the things I cannot change;
courage to change the things I can;
and wisdom to know the difference….

from The Serenity Prayer, by Reinhold Niebuhr

     Picture an early human moving through the quiet forest, intent on the prey he’s tracking. His pace is steady and his mind focused. Suddenly a bear bursts through the trees.  Emotional centers in primitive parts  the hunter’s brain fire off  threat messages which race through the sympathetic nervous system to his adrenal glands—little thumb size organs buried in fat and sitting on top of the kidneys.  Almost instantly, each gland responds with a burst of adrenalin from its central core, the adrenal medulla. Danger also prompts his pituitary gland to pour out a big dose of adrenocorticotropin (ACTH), a hormone that speeds through the blood to the adrenal cortex, the outer 80% of the gland. In response, the gland releases cortisol, a powerful glucocorticoid hormone involved in energy regulation.

The hunter’s pulse and blood pressure shoot up.  His airways dilate and he breathes faster.  His vision narrows and sharpens. Anticipating action, his muscles and liver free glucose and fat from storage.  By the time he races to a nearby tree to haul himself to safety,  the cascade of neural and hormonal events has shifted his metabolism from quiet homeostasis (maintenance of normal function) to an active state designed for fleeing….or for fighting if the bear climbs too.  When the bear loses interest and wanders away, our early man’s activated physiology reverts to routine functioning. He climbs down, resumes his methodical hunt and cooks his game over an open fire. From sundown to sunup, he sleeps.

Now consider a modern man as he rushes through his urban environment. He becomes anxious and then angry when his train is late. As he hails a cab he narrowly misses being hit by an oncoming car. Horns blare.  He flops down in the back seat of the cab, fumbling for his ringing cell phone, only to hear that his boss is angry because he is late.  Inside our overweight modern man’s body,  early hunter physiology whips his adrenal glands into action – over and over and over. But he does not get to fight or flee. Worse yet, the threats in his environment do not lose interest and wander away.  He will be on edge all day, and perhaps late into the night.  After a few drinks, a few smokes, a fast food meal and some paperwork, he falls asleep in front of the TV, finally stumbling into bed in the wee hours of the morning. By 6AM he’s starting over, sleep-deprived.

The adrenal gland connection

In both early and modern humans, the brain-adrenal connection is heavily influenced by environment, genetic makeup, lifestyle and memory of previous experiences. We learn fear and make habits of emotional responses. While animal research can’t take into account human mental components of stress, it has provided useful physical insights, especially about the adrenal connection to chronic stress. Experiments in “rat micro-societies” refined the fight-or-flight concept and divided it into aggressive defense and passive defeat responses, an important distinction because each type activates different parts of the adrenal glands.

Rats responded with passive defeat when a task like pushing a lever sometimes produced food, sometimes didn’t, sometimes in one place, sometimes in another, and sometimes not at all. The consequences of the rats’ actions were uncontrollable and feedback didn’t help them learn.  In these circumstances the adrenal cortex overproduced cortisol.  If you think the passive defeat experiments resemble average life, then you’ll guess, correctly, that chronic stress in people might also trigger elevated cortisol levels.

Aggressive defense responses to the rat equivalent of being mugged, in contrast, activated primarily the adrenal medulla, which takes charge of the immediate activity necessary to survive a threat by producing an adrenalin rush – a burst of the hormones epinephrine and norepinephrine. In states of fear and/or anger, we experience this rush as rapid pulse, elevated blood pressure, increased breathing rate, flushing, pallor and dry mouth.

In our early hunter these adrenal responses are sequential. First comes the adrenalin rush which helps him survive.  Following just behind,  the adrenal cortex ramps up hormone production to help restore normality–to restock energy supplies, dampen pain and divert resources from routine activities.The system is designed for short bursts of danger, not for chronic immersion in mental stress.

The metabolic syndrome connection

Beginning in 2002, researchers began to correlate adrenal hormone abnormalities with the modern plague of the metabolic syndrome—abdominal obesity, insulin resistance, diabetes and high blood pressure, all reliable side effects of exposure to excessive cortisol, whether it comes from drugs like prednisone or from  pituitary or adrenal gland diseases. (See note on Cushing’s disease below).  No one thinks cortisol and stress are wholly responsible for our metabolic epidemic, but many hope that the stress connection will help lead to a solution.

Counteracting the stress response

Stress researchers uniformly conclude that short of retreating from the world, the only major defense that counteracts the effects of stress is regular physical activity which dissipates some of the energy mobilized for action.  The best results come from superimposing physical activity on a lifestyle that accommodates enduring human needs: sufficient sleep, diet suitable for an ancient physiology, good social network and engagement in focused activity that has personal value. Even then, coping strategies are necessary.

A Note on Cushing’s Disease

    The most dramatic demonstration of the results of too much cortisol occurs in patients with Cushing’s disease, usually caused by a pituitary gland tumor which overstimulates  the adrenal cortex.  In these patients, muscles are thin and weak, and excess weight is concentrated in the trunk and face and neck.  Patients have red, jowly faces and skin scored by purplish stretch marks and poorly healed wounds. Bones are robbed of calcium and osteoporotic upper backs round forward under the characteristic “buffalo hump” of fat.  The adrenal cortex hormones also have weak male hormone effects causing male pattern baldness and excess facial hair in women.  The immune system is weakened and health is further damaged by diabetes, high blood pressure and heart disease.

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