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

Mind Games

The arrival of the baby boom generation at the threshold of old age coincides with a technology boom that marries the appeal of computer and video games to updated views on the brain’s neuroplasticity– its capacity to rewire itself even in adulthood. This union has spawned mind game businesses in which clients exercise their brains with computerized games, quizzes and tests. Lumosity and other cognitive training companies (see a sampling below) claim success in improving clients’ mental flexibility, speed, focus, concentration and memory. Well over 60 million subscribers hope their brains benefit from mental workouts in virtual gyms. Is their money well spent?

What is neuroplasticity?

Neuroplasticity refers to the dynamic process of physical change in and between brain cells that occurs in response to experience. When an infant is born, there is ample space between the cells in the outer layer of his brain, where higher functions like seeing, thinking, speaking, planning and remembering will develop. By the time he is two years old, this space between brain cells is tangled with nerve fibers connecting them to each other and to new cells which have migrated in from deeper areas. These changes continue in response to experience and are accompanied by pruning away of some of the initial connections to maximize efficiency and conserve energy.

For years the dogma taught in medical school was that neural circuitry was complete by the early twenties, a concept that was hard to understand because learning is possible at all ages and learning must have some kind of physical basis. But new evidence gradually emerged to prove that the brain continues to rewire itself throughout life. Neuroplasticity persists. The developers of the tools used by the companies like Lumosity seized upon this concept and added to it a wealth of data obtained from cognitive testing by psychologists and neuroscientists about how people think, remember, organize, plan and act. The brain games they devised for mental workouts in virtual gyms  call upon these functions in hope of strengthening the brain circuits they use.

Use the circuits or lose them

Unused brain circuits lose connections just like unused muscle loses size. Hard learned algebra disappears once there are no more tests to call it into use. But there are apparently some traces of initial learning left, because relearning is easier than first time learning. Rusty skills can be brushed up with less effort than their first development required. Brushing up a skill presumably involves a physical process within the networks of nerve cells called upon for the task. It is this process that the virtual brain gyms seek to stimulate and apparently succeed in doing according to at least some measures of improvement.

Virtual mental gyms vs. real life mental exercise

The mental skills exercised by cognitive training programs include memory, attention, mental speed and flexibility, mathematical skills and visual-spatial processing. There is no doubt that exercising these brain functions is beneficial and that, with enough time spent and effort expended, the exercise improves the ability to do the tasks involved. The question is whether or not the improvement in these tasks carries over into real-life reasoning, planning and problem solving abilities. Here the data are murky indeed. It appears that the positive effects of exercising in mental gyms, if measurable, are confined to the types of tasks involved in the exercise and are not sustained for long after the practice ends. Lifetime habits of mental activity have much more persistent influence as people age.

Most people know elderly individuals who have maintained robust minds. They are usually curious about life, resilient, adaptable and habitual seekers of information. These traits inform all of their interactions and activities. They spend their lives in mental gyms of their own construction and prefer active use of their minds over passive entertainment. Very often, they have also remained physically active long into older years.

The brain training programs popular today aim to provide a similar pattern of mental activity in an entertaining way, but the challenges are intermittent and short. If the participant has been on a lifelong course of high mental engagement with the world, and if he happens to enjoy the games and tests he is involved in and is committed to them, his test results after participation are likely to be better than those of someone who has been less active mentally in the past and who does not particularly enjoy the program.

Does mental exercise prevent Alzheimer’s disease?

Does an active, flexible and resilient mind resist Alzheimer’s disease? Since we do not know the cause of this devastating disorder, it is hard to speculate about what might make a brain resistant to the pathology that characterizes the disease – the amyloid plaques and neurofibrillary tangles that scar the brain. But it has long been known that the degree of mental deterioration in life in does not necessarily reflect the amount of scarring seen in the brain at autopsy of the patient with Alzheimer’s disease. Of two people with virtually identical diseased brains at autopsy, the one who had higher levels of mental activity over life – more reading, writing, educational achievement- will have suffered fewer and less severe disease symptoms. But even if this observation is coincidental and mental exercise has nothing to do with protection against the symptoms of Alzheimer’s disease, an actively lived life of the brain has its own rewards beyond preservation of health. And it does not require a virtual gym.

Other options

Though mind games don’t necessarily improve mental functions in daily life, there are no negative effects from engaging in brain training, except, perhaps, on the budget and on time better spent in physical and social activity. Regular modest aerobic activity like walking (preferably outdoors), resistance training such as weight lifting and Pilates exercises, adequate sleep and a supportive and enjoyable social network have all been correlated with better mental functioning in old age. For no fees there are always books, board games, crossword puzzles, jigsaw puzzles, hobbies, crafts, conversations and devotion to others’ needs.


 A Sampling of Reputable Brain Training Programs



         Rosetta Stone Fit Brains

            Brain Fitness by MindSparke

                                                          Brain Gymmer

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