Sleep—Still a Mystery!

Most people spend a full third of their lives asleep, yet most of us do not have the faintest idea what sleep does to our bodies and our brains. Sleep remains one of the secrets of science.¹ However, there is ample evidence indicating that difficulty in falling asleep and non-restorative sleep are associated with the risk of cardiovascular disease in adults and young children. Statistically, after adjusting for lifestyle factors, age and chronic conditions, researchers found men who reported difficulty initiating sleep or experienced non-restorative sleep had a 55% and 32% increased risk of cardiovascular disease mortality over a six-year follow up, respectively, when compared to men who did not report these insomnia-related symptoms.²

In fact, sleep deprivation or insomnia has become a major health problem in the US, crossing all economic lines. A recent report indicated nearly one-third of all working adults get six or fewer hours of sleep each night as opposed to the recommended seven or eight. Insomnia is quite prevalent and affects a large share of the population.³

This article presents a brief overview on several aspects of sleep, including insomnia, and provides suggestions for improving sleep quality. The references should help those who wish to learn more about a process we all experience.

History of Sleep Science

Sleep has been studied for at least 2,500 years, beginning with the Greek philosophers Alcmaeon, Hippocrates and Aristotle. They all provided theories on the causes and functions of sleep.⁴ In 350 BC, Aristotle wrote "On Sleep and Sleeplessness" in which he posed the questions of whether all animals share the need for sleep and whether the soul or the body is affected by sleep. These same questions were debated for the next 2,000 years.

Early observations often placed the source of the sleep function within the stomach, with the idea that warm vapors arose from the gut during digestion to initiate sleep.⁵ Many other theories regarding the origin of sleep were postulated during the 18th and 19th centuries, including the presence of a sleep substance or toxin that built up during the day and dissipated at night. It was not until the 20th century that modern sleep science emerged, prompted by French scientist Henri Pieron, who in 1913 published the first text to consider the physiology of sleep.⁶

A major technological advance in understanding sleep was the ability to measure brain activity during slumber. The first human electroencephalogram (EEG) was performed by German neurologist Hans Berger in 1928, after improvements in electrophysiology allowed him to place electrodes on the human scalp to record the electrical activity of the brain and to demonstrate the differences in brain activity between being asleep versus being awake. Since then, a plethora of new brain-scanning devices have generated an explosion of information elucidating complex and critical processes that occur while we sleep. Sleep research has become one of the most diverse and exciting fields of scientific inquiry in the 21st century, spawning an abundance of intriguing and conflicting theories. For example, while there are a number of theories as to the purpose for sleep, there is still no agreed-upon definition of what sleep actually represents. This puzzle is further confounded by the fact that some species require a 19-hour period of inactivity while others need only two.

Regulating Sleep

According to a recent study, the body uses two mechanisms to regulate sleep. One is the body clock, which attunes humans and animals to the 24-hour cycle of day and night. The other mechanism is the sleep "homeostat," a mechanism in the brain that keeps track of waking hours and makes people drowsy when resetting is necessary. This mechanism represents an internal nodding off point separate from external factors.⁷

Sleep Stages

There are two kinds of sleep-REM (rapid eye movement) sleep and non-REM (NREM) sleep. During REM sleep, the eyes dart quickly back and forth under the eyelids. Dreaming occurs during this stage. REM sleep stimulates areas of the brain responsible for learning and memories. The brain is active and brain waves resemble awake patterns. Breathing is rapid, shallow and irregular, and heart rate and blood pressure increase. This stage plays an essential function that is not fully understood. There are three stages of NREM sleep: drifting in and out of sleep (stage N1), through light sleep (N2) and into deeper sleep (N3). Stage N2 accounts for 40-50% of sleep time. Stage N3 is the most physically restorative, as brain waves slow considerably.⁸ The average adult experiences four to five full sleep cycles--a combination of REM and NREM sleep-- in an eight-hour period. Each cycle lasts about 90 minutes.

Benefits

According to recent research, sleep is important because it weakens the connections among brain cells to save energy, avoid cellular stress and maintain the ability of neurons to respond selectively to stimuli. The scientist conducting the study noted that sleep is the price we pay for learning and memory. While we are awake, learning strengthens the synaptic connections throughout the brain, increasing the need for energy and saturating the brain with new information. Sleep allows the brain to reset, helping integrate newly learned material with consolidated memories.⁹ Studies in mice also indicate the channels in the brain's glial cells (the glymphatic system) can help remove a toxic protein called beta amyloid from brain tissues during sleep. Beta amyloid is known to accumulate in the brains of patients with Alzheimer's disease.¹⁰

Effects of Aging

Sleep quality, particularly the slow wave activity (N3) that occurs during deep sleep, decreases with age. Older adults spend more time in the lightest form of sleep (N1). (This may be due to a drop in melatonin level that normally occurs in the evening in the elderly. Melatonin signals the body to get ready to sleep.) Poor quality and quantity of sleep are associated with declining functional status and quality of life, as well as a greater incidence of depression.¹¹ It has been shown that older adults need as much sleep as younger adults-about seven to eight hours nightly. However, both too little or too much sleep have been associated with increased morbidity and mortality.¹²

Insomnia

Insomnia is defined as difficulty with the initiation, maintenance, duration or quality of sleep resulting in the impairment of daytime functioning, despite adequate opportunity and circumstances for sleep. Transient insomnia lasts less than a week, and short-term insomnia from one to four weeks. Chronic insomnia-lasting more than a month-afflicts 10-15% of the population and occurs more frequently in women, older adults and patients with chronic medical and psychiatric disorders.¹³ The Centers for Disease Control and Prevention estimates about 70 million Americans suffer from sleep problems. Fortunately, effective treatment for most patients, consisting of cognitive behavioral and pharmacologic therapy, is available. Cognitive therapy includes stimulus control, relaxation and sleep hygiene education.

Final Thoughts

One of the most common sleep-related difficulties is the inability to concentrate. It is more likely to occur among people reporting less than seven hours of sleep daily than among those reporting seven to nine hours. Based on these findings, at least one-third of US residents do not get enough sleep on a regular basis, and this situation impairs their ability to perform daily tasks. Chronic sleep deprivation also has a cumulative effect on mental and physical well-being and can exacerbate chronic diseases. Moreover, studies in animals indicate poor-quality sleep marked by frequent waking can speed cancer growth, increase tumor aggressiveness and dampen the immune system's ability to control or eradicate early cancers.¹⁴

There is still much to be learned about the science of sleep. In the meantime, employers may wish to advise employees who seek to improve their sleep quality to: (1) keep a regular sleep schedule; (2) avoid stimulating activities within two hours of bedtime; (3) avoid caffeine, alcohol and nicotine in the evening; (4) avoid going to bed on a full or empty stomach; and (5) sleeping in a dark, quiet, well-ventilated space with a comfortable temperature.¹⁵ Alert employees make fewer mistakes.

References

1. Randall DK. Dreamland: Adventures in the Strange Science of Sleep. New York, NY: WW Norton & Co; 2012.
2. "Insomnia linked to mortality risk." Science Daily. http://www.sciencedaily.com/releases/2013/11/131120112002.htm. Published 21 November 2013. Accessed 2 May 2014.
3. Randall DK. "Rethinking Sleep." The New York Times. 22 September 2012: SR1, New York edition.
4. Lockley SW, Foster RG. Sleep: A Very Short Introduction. New York, NY: Oxford University Press; 2012.
5. Ibid.
6. Ibid.
7. Donlea JM et al. "Neuronal machinery of sleep homeostasis in Drosophila." Neuron. 2014; 81(4): 860-862.
8. Mayo Clinic Health Letter special report. Good night, sleep tight: Get better sleep without taking a pill. February 2014.
9. Tononi G, Cirelli C. "Sleep and the price of plasticity." Neuron. 2014; 81(1):12-14.
10. Welberg L. "Sleep: not such a waste." Nature Reviews Neuroscience. 2013; 14:816-17.
11. Focus on healthy aging. Icahn School of Medicine. Vol 10G-R3. August 2012.
12. CDC Morbidity & Mortality Weekly Report. www.cdc.gov/mmwr/PDF/wk/mm6008.pdf. Centers for Disease Control and Prevention; 2011; 60:239-42.
13. Silber MH. "Chronic insomnia." New Eng J Med. 2005; 353(8): 803-10.
14. "Fragmented sleep accelerates cancer growth." Science Daily.http://www.sciencedaily.com/releases/2014/01/140127100947.htm?utm_source=feedburne. Published 27 January 2014. Accessed 2 May 2014.
15. Age Page. "A good night's sleep." National Institute of Aging website. http://www.nia.nih.gov/health/publication/good-nights-sleep. Updated 24 March 2014. Accessed 2 May 2014.

About the Author

Max Sherman is head of Sherman Consulting Services in Warsaw, IN. RAPS recently published a collection of Sherman's work, From Alzheimer's to Zebrafish: Eclectic Science and Regulatory Stories. He can be reached at [email protected].

Cite as: Sherman M. "Sleep--Still a Mystery!" Regulatory Focus. May 2014. Regulatory Affairs Professionals Society.