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Circadian-RhythmThis paper discusses the Western human circadian rhythm and its relation to health.

1. The circadian rhythm of a modern man

“In 1910, the average American slept nine hours a night, disturbed only by the occasional Model T backfiring. We now average 7.5 and declining.” – Robert Sapolsky (Why Zebras Don’t Get Ulcers)

The typical Western person’s circadian rhythm differs in at least three main ways of which the human species has adapted to in its history

First of all, the amount of light during night time. Before artificial lighting popularized, people spent the night in almost complete darkness . Today, most families live in almost constant light even if it is pitch black outside.

Second, the amount of light during the day is now lower than it has ever been in human history . The reason is that we do not spend much time outdoors. We spend the days indoors, where the amount of light can be over a hundred times less than the amount of light outside.

“Bright light can help shift even the most extreme body clocks,” says Professor Roenneberg. “But the amount of light in most offices is laughable. You would be lucky to get 400 lux [a unit of measurement of the intensity of light] at a bright vertical office window during the day, whereas outside on a cloudy day in summer you would experience more like 10,000 lux. If it’s a blue sky, you could get as much as 150,000 lux.” (Independent: Could you be suffering from ‘social jet lag’?)

The third current problem is sleep duration, which has been decreasing in recent decades.

In a study on connections between sleep and obesity published this year, it was found that in the 1960’s people slept about 8-9 hours a night. By 1995, the amount had shrunk to seven hours. In 2005, a third of the population slept for about six hours a night. Actigraphic and polysomnographic studies show that middle-aged people only get six hours of sleep on average. (Reiter et al. 2011)

Now we are going to speculate the effect of these on health by studying some research material on the subject.

2. The circadian rhythms? connection with health ? shift work and clinical sleep studies

People doing shift work is an interesting group when reflecting on the circadian rhythms’ effects on health. These people must for follow a very unnatural sleep rhythm because of their profession. Epidemiologic data shows that certain health problems are much more common among shift workers than in the average population.

  • Obesity ? In a Swedish study 27485 people answered a survey and according to the results, shift work correlates to a 40% higher risk for obesity (BMI over 30) after adjusting for age and socioeconomic factors. (Karlsson et al. 2001)
  • Breast cancer ? In Denmark the risk of breast cancer in nurses is 80% higher in those working day and night shifts. The longer the shift work had lasted, the larger the risk was. Those who had been working in shifts for over two years, the risk was 160% higher (after adjusting the results) than in those only working during the day. (Hansen&Stevens 2011)
  • Cortisol and obesity ? In the Netherlands a small study (122 persons) showed, that in people doing shift work the amount of cortisol in a hair sample was larger (47 .32 vs 29.72 pg/mg). In young people doing shift work the BMI of these people was clearly higher compared to day workers (27.2 vs 23.7). (Manenschijn et al. 2011)

“If light were a drug, the government would not approve it,” says Professor Charles Czeisler of the Harvard Medical School. And Professor George Brainard of Thomas Jefferson University in Philadelphia, adds: “Humans evolved on a planet without electric light over thousands and thousands of generations. The body is designed to be alert and awake during daytime hours and to sleep at night. Now we have a 24-7 society that isn’t in harmony with our biological design.”

“In the new study, scientists grafted human breast cancer tumours on to rats and infused them with blood taken from women during the day, in the early hours of the morning, and after being exposed to light at night. The blood taken in darkness slowed the growth of the cancers by 80 per cent, but the blood taken after exposure to light accelerated it.” (Independent: Avoid breast cancer. Sleep in the dark…)

If even a few years of shift work can clearly be seen as an elevated risk for breast cancer, could a lifetime of sleep deprivation or other light related problems that affect most people have an effect on the risk of chronic disease? I would say it’s possible.

Some experimental studies have been done, in which for example the test subjects duration of sleep has been reduced.

  • In a study conducted by the University of Chicago, eleven young men were sleep deprived (four hours of sleep per night) for six days. This caused the test subjects? cortisol levels to rise and sugar tolerance to temporarily decline. (Spiegel et al. 1999)
  • The same university published a cross over study, in which 10 overweight people were calorie deprived for two different time periods. During the one period they were allowed to sleep for 8.5 hours and in the other only 5.5 hours. The actual amounts of sleep were 7h 25 min and 5h 14 min. In both groups the subjects weights declined 3 kilograms, but in the sleep deprived group 80% of this weight was muscle. Without sleep deprivation 52% of the dropped weight was muscle and the rest fat. (Nedeltcheva et al. 2010 ; Whole Health Source – The Big Sleep)
  • In an American study conducted in 2009, ten test subjects followed a 28 hour day instead of the normal, 24 hour day. Half way in the study the test subjects spending night time as day time, the test subjects leptin levels were about 20% lower during the day than before the test but during sleep the difference was smaller. Also the insulin levels were on average 22% higher and after breakfast (2h) the blood sugar rose 32% higher than normally. (Scheer et al. 2009)

3. The environmental light and melatonin secretion

Next we’ll dive into the world of melatonin, but first the basics.

The ambient light contributes significantly to the body’s circadian rhythm. In particular, blue light (460-490nm) inhibits the pineal gland from secreting melatonin. Melatonin is often called the dark hormone, because it is secreted at night.

Only blue light affects the secretion of melatonin, so if a person is wearing blue blocker sunglasses, melatonin secretion will not be affected. Of course, removing the short wavelengths (blue light) from lamps will have the same effect. (Sasseville et al. 2006, Kayumov et al. 2007, Chellappa et al. 2011).

Even normal lighting before going to sleep can decrease melatonin secretion which can have effects on health. The melatonin blocking effects of blue light can be significant especially in winter time, when the small amount of daytime exposure to light can cause the body to react more significantly to bright artificial light used in the evening. (Gooley et al. 2011, Higuchi et al. 2007, Park&Tokura 1999).

Only blue wavelengths of light have effect on melatonin secretion, but for example cortisol levels can rise from other wavelengths as well. (Figueiro&Rea 2010, Leproult et al. 2001).

Below are empirical studies in which the amount or type of light has been altered and the results have been documented:

  • In Ohio the effect of blue blocker glasses and their effect on a person’s quality of sleep and mood was studied. Orange colored blue blocking glasses improved quality of sleep, but grey control glasses didn’t. (Burkhart&Phelps 2009)
  • Blue blocker lenses seem to be very effective for insomnia in ADHD subjects. The average PSQI score fell from 11.15 to 4.54, dropping below the cut-off score of 5 for clinical insomnia“. (Fargason et al. 2013)
  • Doctor James Phelps described a small experiment in his article, in which persons (n=21) suffering from bipolar disorder and sleep complications were given blue blocker glasses for evening usage. Nine test subjects felt their condition improve “very much” while eight people didn’t notice any effect. Also a few felt smaller improvement and also a few were somewhat bothered because of falling asleep too early. (Phelps 2008 ; see also Seth Roberts’ blog post Bipolar Disorder: Good Results with Blue-Blocker Glasses).
  • In New York State a study was conducted in which school children wore blue blocker glasses (with orange lenses) during the day for one school week. This caused their melatonin secretion at evening to begin a half an hour later than normally. (Figueiro&Rea 2010)

I believe that the effect seen in the bright light study mentioned before could be replicated and possibly surpassed with ordinary daylight. Expensive bright lights shine light at 10 000 lux at the best, but outside the amount of light can be ten times larger. Daylight might also have other benefits like vitamin D production caused by UV-radiation, the temporary lowering of blood pressure caused by nitric oxide metabolism, plus the stress-relieving effects of red and near-infrared light. The problem of course is, that in the winter time natural light isn’t available in large amounts in all parts of the world. (Holick et al. 2007, Opl?nder et al. 2009, Feelisch et al. 2010, Barrett&Gonzalez-Lima 2013).
Melatonin can also be used as medication and in clinical trials it has been portrayed as quite a useful drug:

  • In one study, melatonin had quite a good effect on irritable bowel syndrome. (Lu et al. 2005)
  • Melatonin supplements might be beneficial to patients suffering from CFS and/or fibromyalgia. The benefits are possibly caused at least in part, by the improvement of subjects? quality of sleep. Those who used melatonin showed significant improvement in sleep / sleep parameters. (Hussain et al. 2011, van Heukelom et al. 2006)
  • According to a recent meta-analysis of melatonin, a slightly higher dose (20mg) seems to be have quite a large effect on conventional cancer treatments. It decreases the mortality rate and reduces treatment side effects significantly. (Wang et al. 2012, see also Mills et al. 2005)

Even though light is very important influence to human / animal circadian rhythm, apparently among light, food, other people and physical activity also have a notable effect. I’m not yet particularly familiar with that data, so it will not be discussed in this essay.
4. Tips for improving sleep and health
Get some light after waking up and during the day

The effect of light on the circadian rhythm seems to be the largest immediately after waking up, so walking outside for ten minutes after waking up can be beneficial.

If you want an adequate amount of blue light during the winter, there are roughly two types of light therapy lamps. Large ones and small ones. The larger lamps have a large lux amount (they are brighter), and the smaller ones compensate with the light spectrum and by a smaller distance between the user and lamp. The lights of small lamps are slightly bluer to compensate for the smaller intensity of light. (Meesters et al. 2011)

I have noticed that if I don’t get enough light during the first 1-2 hours after waking, I’ll stay more or less sleepy for the rest of the day.

Sufficient blue light during the day might be important for alertness, mood and sleep. (Viola et al. 2008)


A light box (left), blue blocker sunglasses (right).

Avoid unnecessary light during the late evening

Turning lamps off and dimming your computer’s display are some of the simplest non-pharmaceutical ways to increase melatonin levels at night. And to make it easier to fall asleep.

If I get a too much light into my eyes at bedtime, I will suddenly become very alert and that means that I need to wait another 1-2 hours until I’ll be able to fall asleep. When I was in high school, this was a significant problem for me. I had to wake up at 7am on almost every morning, yet I usually couldn’t fall asleep before midnight. The late evening, the time when I should have been already sleeping, was the most productive time of the day, because of the strong alerting effect of light at night.

F.lux is a popular computer program that changes the displays color to orangish automatically in the evening. Personally I prefer to use Gamma Panel (gapa.exe), a program that allows you to remove blue light completely from your computer screen.

The blue blocker sunglasses are another alternative. If you want to block out blue light, you can buy some nice lenses from ebay (use keyword “aviator blue blocker”) and wear them in the evenings.

Also red light bulbs (LED) can be used can be used as night reading lamps.

Poor curtains can leave the room too bright during the night or early morning. A sleep mask is an easy and cheap way to correct this problem.

redden computer screen

In the evening, I usually use Gamma Panel software to redden my computer screen. This makes falling asleep much easier.

Nutrition and sleep

A combination of melatonin, magnesium and zinc has been shown to have great results in sleep quality studies. (Rondanelli et al. 2011)

In a few studies, glycine has been shown to improve quality of sleep. The primary source of glycine is collagen protein or gelatin. This means that head cheese and bone broth are a good source of glycine and can improve quality of sleep. I occasionally make jelly out of gelatin and concentrated juice. (Yamadera et al. 2007, Inagawa et al. 2006)

I personally agree with the basics of Matt’s “Eat for Heat” ideology. If I have trouble falling asleep, I try to eat some extra starch and fat calories (e.g. rye/wheat bread with butter and cheese) and avoid too large amounts of fluid.
Other ideas

Seth Roberts, a Professor of Psychology, has written a lot about his various experiments, some of which are related to circadian rhythm. (Roberts 2004; Seth’s blog; Perfect Health Diet – Seth Roberts and Circadian Therapy)

Here’s a list of things that, according to Roberts’ experiments, could benefit those having problems related to their diurnal rhythm.

  • Intake of vitamin D3 might affect one’s circadian rhythm if the doses are high enough. Because of this, Roberts has recommended taking 4000IU (100?g) of vitamin D shortly after waking up. (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)
  • Standing so much that your legs become fatigued might be useful. Roberts noticed consistently high quality of sleep when he stood at least 9 hours during a day. He also noticed that this time can be dramatically reduced by standing on one leg. (1 (p.13-15) ja 2)
  • Morning Faces Therapy: According to Roberts, if one sees faces after waking up, he/she will be more sleepy and unmotivated in the evening, but more alert and motivated in the next morning. (1 ja 2 (p. 5-13)


A mirror, to see my own face during my piano improvisations. (Seth Roberts' faces therapy)

A mirror, to see my own face during my piano improvisations. (Seth Roberts’ faces therapy)


Thanks to Laura Mikkonen for doing most of the translating work.

Appendix I: Extra references

1989:?Ford&Kamerow: Epidemiologic study of sleep disturbances and psychiatric disorders. An opportunity for prevention??“The risk of developing new major depression was much higher in those who had insomnia at both interviews compared with those without insomnia (odds ratio, 39.8; 95% confidence interval, 19.8 to 80.0).”

1995:?Morita et al. Inhibitory effect of light of different wavelengths on the fall of core temperature during the nighttime.

1999:?Blask et al. New actions of melatonin on tumor metabolism and growth.?“Melatonin is an important inhibitor of cancer growth promotion while the essential polyunsaturated fatty acid, linoleic acid is an important promoter of cancer progression. […]?While melatonin inhibits tumor linoleic acid uptake, metabolism and growth, pinealectomy or constant light exposure stimulates these processes.

H?bert et al.Nocturnal melatonin secretion is not suppressed by light exposure behind the knee in humans.

2000:?Pinchasov et al. Mood and energy regulation in seasonal and non-seasonal depression before and after midday treatment with physical exercise or bright light.?One week of bright light treatment (2-h exposure to 2500 lux between 14.00 and 16.00 h) increased oxygen consumption in nine winter depressives and nine non-depressed subjects, while no significant change in oxygen consumption was found in nine subjects with non-seasonal depression. Weight loss was observed in the groups treated with physical exercise and in the group of light-treated winter depressives.”

2004:?Claustrat et al. Melatonin secretion is supersensitive to light in migraine.?“These findings show a clear hypersensitivity to light in young female migraineurs during the headache-free period.”

Mistlberger&Skene: Social influences on mammalian circadian rhythms: animal and human studies.

2005:?Higuchi et al. Relationship between individual difference in melatonin suppression by light and habitual bedtime.

Barbini et al. Dark therapy for mania: a pilot study.

2006:?Rybak et al. An open trial of light therapy in adult attention-deficit/hyperactivity disorder.?“Morning bright light therapy was associated with a significant decrease in both subjective and objective measures of core ADHD pathology, improved mood symptoms, and a significant phase advance in circadian preference. Multiple regression showed that the shift toward an earlier circadian preference with LT was the strongest predictor of improvement on both subjective and objective ADHD measures.”

Pignone et al. Melatonin is a safe and effective treatment for chronic pulmonary and extrapulmonary sarcoidosis.

2008:?Fuller et al. Differential rescue of light- and food-entrainable circadian rhythms.?“When food is plentiful, circadian rhythms of animals are powerfully entrained by the light-dark cycle. However, if animals have access to food only during their normal sleep cycle, they will shift most of their circadian rhythms to match the food availability.”

2009:?Kent et al. Effect of sunlight exposure on cognitive function among depressed and non-depressed participants: a REGARDS cross-sectional study.?“Among depressed participants, a dose-response relationship was found between sunlight exposure and cognitive function, with lower levels of sunlight associated with impaired cognitive status (odds ratio = 2.58; 95% CI 1.43-6.69).”

Bennett et al. Use of modified spectacles and light bulbs to block blue light at night may prevent postpartum depression.?“all new mothers may benefit from using glasses and light bulbs that block blue light when getting up at night to care for their babies.

Cohen et al. Sleep habits and susceptibility to the common cold.?“There was a graded association with average sleep duration: participants with less than 7 hours of sleep were 2.94 times (95% confidence interval [CI], 1.18-7.30) more likely to develop a cold than those with 8 hours or more of sleep. The association with sleep efficiency was also graded: participants with less than 92% efficiency were 5.50 times (95% CI, 2.08-14.48) more likely to develop a cold than those with 98% or more efficiency.”

2010: Fonken et al. Light at night increases body mass by shifting the time of food intake

2011: Al Robaee&Alzolibani: Narrowband ultraviolet B phototherapy improves the quality of life in patients with psoriasis.

2012:?Figueiro et al. Light modulates leptin and ghrelin in sleep-restricted adults.

2013:?Bedrosian et al. Nocturnal Light Exposure Impairs Affective Responses in a Wavelength-Dependent Manner (pdf)?“Our results demonstrate that exposure to LAN [light at night] influences behavior and neuronal plasticity and that this effect is likely mediated by ipRGCs. Modern sources of LAN that contain blue wavelengths may be particularly disruptive to the circadian system, potentially contributing to altered mood regulation.”
Appendix II: Articles, forum threads etc.

Wikipedia – Phase response curves in circadian rhythms

Perfect Health Diet – Intermittent Fasting as a Therapy for Hypothyroidism

CNN: Trouble sleeping? Maybe it’s your iPad

NY TIMES: In Eyes, a Clock Calibrated by Wavelengths of Light

NY TIMES: Sleeping (or Not) by the Wrong Clock

Lowcarber Forums – Lights Out: Sleep, Sugar and Survival by T.S. Wiley?(The thread is OK but I don’t recommend Wiley’s book to anyone. It’s a very poorly written book.)

Independent: Could you be suffering from ‘social jet lag’?

Slumber’s Unexplored Landscape – People in traditional societies sleep in eye-opening ways

Telegraph: This could be your dream diet

Chicago Tribune – Blue light has a dark side

Can lamps cause epileptic or other types of seizures?

Great Sleep! Reduced Cancer!: A Scientific Approach to Great Sleep and Reduced Cancer Risk (a somewhat interesting book)

LA Times: Exposure to light at night may contribute to depression, study says

Matt Metzgar: The Dark Sky Association

Matt Metzgar: Total Darkness Time

Suppversity – Circadian Rhythmicity – Sunlight, Bluelight, Backlight: How Street Lamps, iPads & Co Mess W/ Our Internal Clock. Plus: Tweaks, Tools & Apps to Prevent Negative Side-Effects