By Dr. Mercola
When you climb into bed for the night, is your bedroom "littered" with dim light from streetlights, passing traffic, a computer, night-light or television set?
Even if the light is so dim that you can easily sleep through it, light pollution can prompt biological changes that have a very significant, and potentially serious, impact on your physical and mental health.
Obvious examples would be the glow that can be seen from miles outside of a big city, or the absence of stars in the night sky if you live in an urban environment.
More subtle examples of light pollution are the strips of light that come in around your curtains at night, or even the glow from your clock radio.
All of these light sources disrupt the natural rhythms of nature, as like most other creatures, humans need darkness. When this natural rule is violated, the consequences can be steep …
Dim Light at Night May Lead to Depression
A study done with hamsters at Ohio State University Medical Center has found that chronic exposure to dim light at night can cause signs of depression after just a few weeks.1 The study also showed changes in the hamsters' hippocampus similar to brain changes seen in depressed people. They pointed out that rates of depression have risen along with exposure to artificial light at night:
"Exposure to artificial light at night (LAN) has surged in prevalence during the past 50 years, coinciding with rising rates of depression."
The link could be due to the production of the hormone melatonin, which is interrupted when you're exposed to light at night. There are many studies that suggest melatonin levels (and by proxy light exposures) control mood-related symptoms, such as those associated with depression -- especially winter depression (aka, seasonal affective disorder, or SAD).
In a study published by researchers at the Oregon Health and Science University (OHSU), it was found that melatonin relieved SAD.2 The study found insomniacs have a circadian misalignment in which they are "out of phase" with natural sleeping times.
This misalignment can be corrected either by exposure to bright lights (during daylight hours), or by taking a melatonin supplement at a certain time of day. While your body will begin to produce melatonin only after it's dark outside, the level of melatonin produced is related to the amount of exposure you have had to bright sunshine the previous day; the less bright light exposure the lower your melatonin levels.
Yet another study about melatonin and circadian phase misalignment found a correlation between circadian misalignment and severity of depression symptoms.3
Studies have also linked low melatonin levels to depression in a variety of populations, including multiple sclerosis patients4 and post-menopausal women.5 Clearly, anything that negatively effects melatonin production is likely to have a detrimental effect on your mood. Melatonin's immediate precursor is the neurotransmitter serotonin, which is a major player in uplifting your mood.
Too Much Light at Night May Also Contribute to Cancer
Normally, your brain starts secreting melatonin around 9 or 10 pm, which makes you sleepy. These regularly occurring secretions thus help regulate your sleep cycle.
The good news is the condition appears to be reversible by simply going back to regular light-dark cycles and minimizing exposure to artificial light at night. But when light receptors in your eyes are triggered, such as by the glow from your television set, they signal your brain to 'stay awake.' To do that, your brain stops secreting melatonin, which is not only a hormone but also a potent antioxidant against cancer.
Melatonin is secreted primarily in your brain and at night it triggers a host of biochemical activities, including a nocturnal reduction in your body's estrogen levels. It's thought that chronically decreasing your melatonin production at night -- as occurs when you're exposed to nighttime light – thereby allows your body to be exposed to higher estrogen levels, which increases your risk of developing estrogen-sensitive cancers, such as breast cancer.6
In addition to dampening your mood and increasing your cancer risk, a confused body clock from too much light exposure at night can result in increased appetite and unwanted weight gain.
Light at Night Might Even Make You Fat
Exposure to light during the night can seriously impact your body's internal clock, even leading to metabolic changes and weight gain. In fact, mice that were exposed to dim light during the night gained 50 percent more weight over an eight-week period than mice kept in complete darkness at night.7 They also had increased levels of glucose intolerance, a marker for pre-diabetes.
The weight gain occurred even though the mice were fed the same amount of food and had similar activity levels, and the researchers believe the findings may hold true for humans as well.
When mice were exposed to nighttime light, they ended up eating more of their food when they would normally be sleeping and this lead to significant weight gain. However, in a second experiment when researchers restricted meals to times of day when the mice would normally eat, they did not gain weight, even when exposed to light at night.
This suggests that the timing of your meals, for instance eating late at night when you'd normally be sleeping, may throw off your body's internal clock and lead to weight gain. In this case, the artificial light, such as a glow from your TV or computer, can serve as a stimulus for keeping you awake and, possibly, eating, when you should really be asleep.
In other words, while it's typically thought that your biological clock is what tells you when it's time to wake up or go to sleep, light and dark signals actually control your biological clock. In turn, your biological clock regulates your metabolism. So when your light and dark signals become disrupted it not only changes the times you may normally eat, it also throws your metabolism off kilter, likely leading to weight gain.
More Consequences of Nighttime Light Exposure
Your circadian rhythm has evolved over many centuries to align your physiology with your environment. However, it is operating under the assumption that you're still behaving as your ancestors have for countless generations: sleeping at night and being awake during the day.
If you push these limits by staying up late at night, depriving yourself of sleep, or even being exposed to the glow from your computer when you should be sleeping, your body doesn't know whether it should be producing chemicals to tell you to go to sleep, or gear up for the beginning of your day.
But maintaining this natural circadian rhythm affects far more than just your sleep pattern. Your body actually has many internal clocks -- in your brain, lungs, liver, heart and even your skeletal muscles -- and they all work to keep your body running smoothly by controlling temperature and the release of hormones.
Disrupting your natural rhythm can also make you more vulnerable to disease, including not only cancer, as mentioned above, but also many others. A report from the American Medical Association highlighted the health risks that changes in circadian rhythms pose: 8
- Carcinogenic effects related to melatonin suppression, especially breast cancer
- Depression and mood disorders
- Reproductive problems
"The natural 24-hour cycle of light and dark helps maintain precise alignment of circadian biological rhythms, the general activation of the central nervous system and various biological and cellular processes, and entrainment of melatonin release from the pineal gland. Pervasive use of nighttime lighting disrupts these endogenous processes and creates potentially harmful health effects and/or hazardous situations with varying degrees of harm."
The Damage is Reversible!
Even though too much light at nighttime causes undeniable health damage, it appears you can undo some of the harm by turning out the lights … in the featured study, the hamsters depressive symptoms went away when they were allowed eight hours of darkness each day.
For you, this may mean turning off your laptop and television earlier than normal, or conducting a light check of your bedroom to wipe out any light pollution creeping in. Even very low levels of light can be enough to suppress melatonin production, so it's important to keep your sleeping environment as pitch-black as possible. If your bedroom is currently affected by light pollution, you will notice a major improvement when you eliminate it. To get your room as dark as possible, consider taking the following actions:
- Install blackout drapes
- Close your bedroom door if light comes through it; if light seeps in underneath your door, put a towel along the base
- Wear an effective face mask that blocks out light -- a very inexpensive solution and very easy to implement when you are travelling. Many hotels I stay at during my travels do not have blackout drapes so I use this to get darkness at night. Also useful for sleeping on planes at night.
- Get rid of your electric clock radio (or at least cover it up at night)
- Avoid night lights of any kind
- Keep all light off at night (even if you get up to go to the bathroom) -- and this includes your computer and TV (computer screens and most light bulbs emit blue light, to which your eyes are particularly sensitive simply because it's the type of light most common outdoors during daytime hours. As a result, they can disrupt your melatonin production)
- If possible, avoid working any night shifts.
- Please note that red light has a wavelength that has minimal impact on your melatonin production. I actually use a red LED alarm clock in my normally very dark room so I know what time it is, as the alarm will cause adrenal stress.
Neat Gadget to Help Evaluate Your Sleep Quality
Over the last two years I have been playing with an interesting device that monitors your sleep at night. It measures
- Total time slept, including when you fall asleep and wake up
- Type of sleep, including, deep sleep, light sleep and REM
- Number of times and how long you were awake during the night
The company has worked with a number of prominent sleep scientists and they have reviewed the data above and developed an algorithm for creating a single sleep score that you can easily monitor over time. The advantage of this is that you can play with a number of different variables such as what time you go to bed, exercise levels, and different foods, and objectively analyze its impact on your sleep pattern.
Initially I was reluctant to use the device and did not for some time as the device actually transmitted the data in real time to a clock radio. Although that is still possible, I do not recommend using this mode due to the EMF exposure. So rather you can merely use it as a sensor that records the data and in the morning you can use Bluetooth to transfer to your smartphone or tablet device. It is a really slick device and I consider it an important part of my health strategy. You can pick it up on Amazon for about $90.