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Tune in to your Sleep Cycle & Prevent Sleep Debt


Research Shows Poor Sleep Is Linked To Numerous Diseases

By: Nathan Daley, MD, MPH
Integrative Preventive Medicine
Integrative Performance Medicine

How often do you awake in the middle of night and sit quietly for one to three hours, while enjoying the serenity and peace of the night and the starry sky outside? Most likely you answered “not often” or “never.” In contrast, being awake for an hour or more in the middle of the night is a miserable experience for most of us. However, in the absence of artificial lighting and during the winter season with its long nights, waking in the middle of night appears to be part of our natural rhythm. In “At Days Close” historian Roger Ekirch reviews historical documents from pre-industrial times (before electric and gas lighting), which indicate that most people had a “first sleep” for a little more than four hours, a “night watch” for one to three hours in which they were awake but in the dark, and then a “second sleep” for a little more than four hours. Numerous anthropologists have commented on this same pattern of sleep in various indigenous populations living without light at night or light pollution from nearby civilization. These people would simply sit quietly and observe the starry sky and the dark, listen to surrounding nature, or quietly (and even silently) interact with others who are awake at the same time.
Unlike most of us, these pre-industrial and indigenous populations were not deprived of sleep, and had no sleep debt (the cumulative deficit of sleep over time). They slept according to the seasonal variations in light and dark without the interference of artificial light at night (LAN). In temperate climates this may have averaged around 7 hours of total sleep each night in the summer and 9 hours of total sleep each night in the winter, averaging around 8 hours of sleep each night for the year. Perhaps just as importantly, they were not deprived of darkness. For these populations, dark time was longer than sleep time.
In modern times, with endless sources of lighted stimulation shining into the night, few of us are getting enough sleep and dark time starts and ends when we turn off or on the lights just before or after sleep. The current consensus about sleep debt is that it has to be repaid minute for minute. Any sleep deprivation at any time in life will remain as sleep debt until we compensate with extra sleep. This is rarely done, however, and many of us are at risk for sleep bankruptcy. If I were to calculate my sleep debt from the last 10 years of medical training and from having young kids, assuming I need an average of 8 hours per night, it comes out to 5,475 hours of debt. If the universe cooperated and I were to work diligently at getting 8.5 hours of sleep each night going forward, it would take me 30 years to climb out of sleep debt! Considering that the natural exposure to darkness is even longer than natural sleep time, my “dark debt” must be even larger!
Sleep debt and dark debt from light at night, altered circadian rhythms, sleep disorders, or working through the night carry some heavy health consequences. Various studies have suggested that such disruption likely contributes to obesity, diabetes, depression, cognitive impairment, infectious diseases, and cancer. It is well known that blue wavelength light at night suppresses melatonin production. Artificial lighting contains a great deal of blue wavelength light, but the moon, stars, candle light, and fire light largely consist of red-orange-yellow wavelengths. These wavelengths do not suppress melatonin production. Melatonin is a powerful immune modulating and tumor inhibiting hormone and melatonin deficiency heavily contributes to the adverse health outcomes seen with sleep and dark debt, but the physiology is much more complex and reaches beyond melatonin. Melatonin deficiency does not explain the increased obesity and cognitive impairment from sleep deprivation, nor does it explain why hormone sensitive cancers like breast cancer and prostate cancer are more significantly related to sleep and circadian disruption. While these complex mechanisms remain to be explained, it is clear that sleep and darkness are essential for health and quality of life. While somewhat of a tangent, it is interesting to note that most of us are also deprived of bright light during the daytime. Indoor lighting is much dimmer than natural outdoor light, even on a cloudy day. Lack of natural bright light may contribute to depression and fatigue.
So the question is, how do we prevent sleep debt and dark debt? Well, there are many opportunities to intervene for better sleep and longer darkness. A number of blue light blocking products are available at, including light bulbs and screen filters for computer monitors and the iPad. Use this technology after dusk to begin producing melatonin and help transition into sleep. The most important step, however, is to simply recognize the critical roles that sleep and darkness play in maintaining our health and to prioritize these experiences. We regard sleep as a time when nothing happens, and darkness as an unproductive or even dangerous period of time. On the contrary, these are highly active and productive times for health. Nighttime and dreaming offer a very different experience of the world, which can be fascinating. We must awaken to the mystery and phenomena of night. Enjoy the stars and moon, the peace and stillness, and the rejuvenating rest that dominate the nighttime experience. Quite literally, without darkness, sleep, and dreams tonight, there can be no hope for a bright and healthy tomorrow.

About Nathan Daley, MD
Nathan Daley, M.D., M.P.H., is residency trained in preventive medicine, integrative medicine, diagnostic radiology, and environmental health. After receiving an undergraduate degree in Microbiology and his M.D. from the University of Oklahoma, Dr. Daley underwent a clinical internship and diagnostic radiology training at the Mayo Clinic in Jacksonville, Florida. Frustrated by the overemphasis on end-stage disease and lack of health-oriented pursuits in modern medicine, Dr. Daley began investigating the origins of health from an ecological perspective involving gene-environment relationships and an individual’s way of interacting with the environment. His insights in these areas will make a substantial difference in your life, health, and well-being.
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Ekirch R. At Day’s Close: night in times past. W.W. Norton and Company, Inc. 2005.
Chepesiuk R. Missing the dark: health effects of light pollution. Environ Health Perspect. 2009 Jan;117(1):A20-7.
Kloog I., et. Al. Light at night co-distributes with incident breast but not lung cancer in the female population of Israel. Chronobiol Int. 2008 Feb;25(1):65-81.
Kloog I., et. Al. Global co-distribution of light at night (LAN) and cancers of prostate, colon, and lung in men. Chronobiol Int. 2009 Jan;26(1):108-25.
Kloog I., et. Al. Nighttime light level co-distributes with breast cancer incidence worldwide. Cancer Causes Control. 2010 Dec;21(12):2059-68. Epub 2010 Aug 3.
Reiter RJ, Tan DX, Korkmaz A, Ma S. Obesity and metabolic syndrome: Association with chronodisruption, sleep deprivation, and melatonin suppression. Ann Med. 2011 Jun 13. [Epub ahead of print]

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