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  • Virtually every organ in your body has its own circadian clock, and to keep them all in sync, you need to keep a regular waking and sleeping schedule that is linked to the rising and setting of the sun
  • Bright daylight exposure is important. If you are in relative darkness all day long, your body will not optimize your melatonin production, and that can have some rather significant ramifications for your health
  • At night, darkness should prevail. Avoid watching TV or using your computer for at least an hour prior to bed, and make sure you sleep in as close to complete darkness as possible

To Sleep Better, Spend More Time in the Dark

April 23, 2015 | 269,359 views
| Available in EspañolDisponible en Español

By Dr. Mercola

Recent research1 reveals that you have more than one biological clock in your body. As it turns out, virtually every organ in your body has its own clock or circadian rhythm, and in order to keep them all in sync, you need to keep a regular waking and sleeping schedule that is linked to the rising and setting of the sun.

When your sleep schedule is erratic, a cascade of effects can occur, raising your blood pressure, altering hunger hormones, and disrupting your blood sugar control, for example.

Chronic sleep disruptions also promote metabolic dysfunction that can result in weight gain and type 2 diabetes. It also increases C-reactive protein, an inflammatory marker associated with deadly heart attacks.

Basically, the various systems in your body are programmed to perform scheduled tasks at specific times during the 24 hour wake-sleep cycle, and when you consistently act against these clocks, your internal systems start to malfunction.

Shift workers who stay awake all night and sleep during the day are especially at risk.

For example, three years of intermittent night shift work can increase your risk for diabetes by 20 percent, and this risk continues to rise with time. Shift workers also have higher rates of obesity, and a four- to five-fold higher rate of cancer than the average population.

How Light and Darkness Influences Your Health

Ever since the advent of the light bulb, people have become increasingly “darkness deficient” at night, while simultaneously getting too little light during the day, courtesy of working indoors. 


The brightness of the light matters, because your pineal gland produces melatonin roughly in approximation to the contrast of bright sun exposure in the day and complete darkness at night.

If you are in relative darkness all day long, it can't appreciate the difference and will not optimize your melatonin production, and that can have some rather significant ramifications for your health.

We now know that a whole host of physiological processes are directed by your endogenous circadian rhythm, which is calibrated to the rising and setting of the sun—provided you’re exposed to natural sunlight and darkness. As explained in the featured article:2

“The light – and the dark – are important signals for the cycle. This circadian rhythm has developed over three billion years as life evolved on Earth in the context of the sun’s day/night cycle. It is built deeply into our genetic makeup.

During the night, in the dark, body temperature drops, metabolism slows, and the hormone melatonin rises dramatically. When the sun comes up in the morning, melatonin has already started falling, and you wake up.

This natural physiological transition into and out of night is of ancient origin, and melatonin is crucial for the process to proceed as it should.

If you were to put someone in a dark cave with no time cues at all, the cycle will last about 24 hours, but not exactly. Without time cues like those from the sun, eventually that person would become out of sync with people outside.”

Aside from lowering body temperature, slowing metabolism, and raising melatonin, your body also undergoes a number of other changes when in the dark. For example, levels of the hunger hormone leptin rises, which decreases feelings of hunger.

Research3 has shown that when you’re exposed to light at night, even if it’s brief, your leptin level decreases, which makes you hungry in the middle of the night—a phenomenon that wouldn’t have been very convenient for our ancestral hunter-gatherers.

Gene expression is also affected by your endogenous circadian clock, as is cellular growth and repair, and hormone production. Exposing yourself to light at night leads to the disruption of all of these processes, setting the stage for diseases like obesity, diabetes, cancer, and depression.

Different Wavelengths of Light Have Different Effects

While the light emitted from the sun is “full-spectrum” light, it has a strong blue, short wavelength light that makes you alert and awake. It also has a potent mood-boosting effect.

In fact, according to one 2010 study,4 blue light appears to play a key role in your brain's ability to process emotions, and its results suggest that spending more time in blue-enriched light could help prevent seasonal affective disorder (SAD).

Getting a healthy dose of sunlight first thing in the morning will help “reset” your circadian clocks, as will getting at least 30 minutes of sunlight during the brightest part of the day, right around noon.

In the evening, however, blue light is inadvisable as it tricks your body into thinking that it’s still daytime. It does this by inhibiting the production of melatonin.  

One 2011 study5 compared daily melatonin profiles in individuals living in room light (<200 lux) vs. dim light (<3 lux). Results showed that, compared with dim light, exposure to room light before bedtime suppressed melatonin in 99 percent of individuals, and shortened the time period when the body has an elevated melatonin level by about 90 minutes.

Melatonin is a regulator of your sleep cycle, and when it is suppressed, there is less stimulation to promote sleepiness at a healthy bedtime. Melatonin is also a powerful antioxidant and free radical scavenger that helps combat inflammation as an integral component of your immune system. It may even have a role in slowing the aging of your brain.

Even more importantly, melatonin has been proven to have an impressive array of anti-cancer benefits.6 It not only inhibits the proliferation of a wide range of cancer cell types, it also triggers cancer cell apoptosis (self destruction) and promotes anti-angiogenesis, meaning it prevents the growth of blood vessels that feed the growing tumor.

Somewhere between 50-1,000 lux is the activation range within which light will begin to suppress melatonin production. However, wavelength is important here as (long-wavelength) red and amber lights will not suppress melatonin while (short-wavelength) blue, green, and white lights will.7

Moreover, the range of light that inhibits melatonin is fairly narrow — 460 to 480 nm. So to promote healthy melatonin production, shift to a low wattage bulb with yellow, orange, or red light as soon as the sun goes down. A salt lamp illuminated by a 5-watt bulb falls within this ideal color range. Electronics such as tablets, phones, computers, and compact fluorescent lamps (CFL) all emit blue light, and are therefore best avoided for at least an hour or more before bedtime.

Night Owls Have Higher Risk of Metabolic Dysfunction

Another recent study8,9 demonstrating how living out of sync with the rising and setting of the sun can affect your health was published in the Journal of Clinical Endocrinology & Metabolism. Here, night owls were found to be more prone to having diabetes, metabolic syndrome, and sarcopenia (muscle loss) compared to those who got up and went to bed early, despite getting the same amount of sleep.

According to study author Nan Hee Kim, MD, PhD:10

“Regardless of lifestyle, people who stayed up late faced a higher risk of developing health problems like diabetes or reduced muscle mass than those who were early risers. This could be caused by night owls' tendency to have poorer sleep quality and to engage in unhealthy behaviors like smoking, late-night eating and a sedentary lifestyle... Considering many younger people are evening chronotypes, the metabolic risk associated with their circadian preference is an important health issue that needs to be addressed.”

Simple Strategies to Optimize Your Body Clocks’ Synchronization

In terms of practical advice to help you maintain healthy synchronization of your circadian clocks, make sure you get bright light exposure during the day. Keep in mind that many indoor environments simply aren't intense enough, so try to get outdoors for at least 30 minutes. Sixty minutes is even better. This will “anchor” your circadian rhythm and make it less prone to drifting if you’re exposed to light later in the evening. The ideal time to go outdoors is right around solar noon but any time during daylight hours is useful.

During winter months, or in situations when you cannot get outside during the day, a blue-light emitter like goLITE BLU11 can be helpful. It's a small light therapy device you can keep on your desk. Using it twice a day for about 15 minutes will help anchor your circadian rhythm. At night, the reverse needs to occur. Now, darkness should prevail, starting about an hour or so prior to bedtime.

This means abstaining from watching TV or using your computer, as electronics emit blue light. If you must use a computer or cell phone, consider installing a free computer program called f.lux.12 It alters the color temperature of your computer screen as the day goes on, pulling out the blue wavelengths as it gets later. In addition to dimming your lights and/or using salt lamps for illumination, there are also special blue light-blocking bulbs you can buy.

When it comes time to sleep, aim to make your bedroom as dark as possible. Simply closing your eyes is not enough, as light can still penetrate your eyelids. I recommend installing blackout shades for this purpose. In my house, I installed accordion pleated blackout drapes. Opt for shades that are on a track, otherwise light may still leak through.

Another inexpensive alternative is to use a sleep mask. Also keep in mind that digital alarm clocks with blue light displays could have a detrimental effect, so if you have to have an LED clock, opt for one with a red display, and set it on its dimmest setting.

More Tips That Can Help Improve Your Sleep

Small adjustments to your daily routine and sleeping area can go a long way toward ensuring you uninterrupted, restful sleep—and thereby better health. In addition to what was already discussed above, the following suggestions can also be helpful if you’re still having trouble falling or staying asleep. You can also review my 33 Secrets to a Good Night's Sleep for even more tips.

Address mental states that prevent peaceful slumber A sleep disturbance is always caused by something, be it physical, emotional, or both. Anxiety and anger are two mental states that are incompatible with sleep. Feeling overwhelmed with responsibilities is another common sleep blocker. To identify the cause of your wakefulness, analyze the thoughts that circle in your mind during the time you lie awake, and look for themes. Many who have learned the Emotional Freedom Technique (EFT) find it is incredibly useful in helping them to sleep. One strategy is to compile a list of your current concerns, and then “tap” on each issue. To learn how to tap, please refer to our free EFT guide.
Keep the temperature in your bedroom below 70 degrees Fahrenheit Many people keep their homes too warm (particularly their bedrooms). Studies show that the optimal room temperature for sleep is between 60 and 68 degrees Fahrenheit.
Take a hot bath 90 to 120 minutes before bedtime This raises your core body temperature, and when you get out of the bath it abruptly drops, signaling your body that you’re ready for sleep.
Develop a relaxing pre-sleep routineGoing to bed and getting up at the same time each day helps keep your sleep on track, but having a consistent pre-sleep routine or “sleep ritual” is also important. For instance, if you read before heading to bed, your body knows that reading at night signals it’s time for sleep. Sleep specialist Stephanie Silberman, PhD suggests listening to calming music, stretching, or doing relaxation exercises.13 Mindfulness therapies have also been found helpful for insomnia.14
Avoid alcohol, caffeine, and other drugs, including nicotineTwo of the biggest sleep saboteurs are caffeine and alcohol, both of which also increase anxiety. Caffeine’s effects can last four to seven hours. Tea and chocolate also contain caffeine. Alcohol can help you fall asleep faster, but it makes sleep more fragmented and less restorative. Nicotine in all its forms (cigarettes, e-cigs, chewing tobacco, pipe tobacco, and smoking cessation patches) is also a stimulant, so lighting up too close to bedtime can worsen insomnia. Many other drugs can also interfere with sleep.
Use a fitness tracker to help you get to bed on time, and track which activities boost or hinder deep sleepTo optimize sleep you need to make sure you’re going to bed early enough. If you have to get up at 6:30am, you’re just not going to get enough sleep if you go to bed after midnight. Many fitness trackers can now track both daytime body movement and sleep, allowing you to get a better picture of how much sleep you’re actually getting. Newer fitness trackers like Jawbone’s UP3, which should be released later this year, can even tell you which activities led to your best sleep and what factors resulted in poor sleep.
