Sleeping in total darkness is a crucial part of sleep hygiene that many overlook. Exposure even to a dim night-light may cause physical changes in the part of your brain called the hippocampus, which, as this Ohio State University hamster study showed, can set the stage for depression.

In fact, sleeping in total darkness is so important that nighttime light has been dubbed “light pollution” by the International Dark-Sky Association (IDA).

Light pollution refers to “any adverse effect of artificial light, including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste,” as defined by the IDA. More subtle examples of light pollution are the strips of light that sneak in around your curtains at night, or even the soft blue glow of your clock radio.

All of these have the potential to negatively impact your health by altering your circadian rhythms. IDA writes:

“Light pollution wastes energy, affects astronomers and scientists, disrupts global wildlife and ecological balance, and has been linked to negative consequences in human health.”

Light pollution has been shown to disturb animals and ecosystems, including the following:

• Interfering with bird migration -- causing birds to collide or circle lights until they die of exhaustion.
• Disrupting the behavior of sea turtle hatchlings, which navigate by the light of the moon. Manmade coastal lighting confuses them, drawing them away from the ocean instead of toward it.
• Interfering with the communication of glowworms and fireflies.
• Nighttime lighting from sports stadiums disrupts the mating activity of nearby frogs.

And now, it appears that nighttime light may physically alter your brain and set you up for depression.

Edison Changed Everything

In an interesting article about the evolution of human sleep, integrative medicine physician and professor at the UCLA School of Medicine Dr. Hyla Cass discusses how the introduction of the campfire was a welcome comfort to early man because, in addition to being a source of warmth, it offered some protection from the hungry beasts that hunted them.

Cass writes:

“It was not that long ago in evolutionary history that we were prey, and the nighttime was filled with silent terrors. After a long, hard day of hunting and gathering, our ancestors would huddle together for safety, such as it was, to endure another night of uneasy sleep, always mindful of the hungry beasts out there ... perhaps close by ... that they could not see.”

This was the beginning of the alteration of our natural cycle of light and dark, and it set the stage for a variety of medical ills our ancestors could not have imagined so many generations beyond.

Campfires were only the beginning of our fascination with altering our natural living and sleeping patterns. Gone are the days of sleeping and awaking with the sun. Thomas Edison made it possible for our nights to be as bright as our days. But, convenient as this is, electrical lighting has come at a price.

Melatonin: Elixir of the Night

While electricity and efficient lighting have clearly provided major benefits to society, we have sacrificed the function of our inner clocks.

Organisms -- human and otherwise -- evolved to adjust themselves to predictable patterns of light and darkness in a physiological cycle known as circadian rhythm. Once artificial light effectively varied the length of our day, the average person’s sleep decreased from around nine consistent hours to roughly seven, varying from one night to the next.

This irregularity prevents your brain from settling into a pattern, creating a state of perpetual "jet lag."

One unforeseen effect is disruption in melatonin production. Melatonin is a hormone secreted in your brain primarily at night (by your pineal gland), triggered by the absence of light. Melatonin’s immediate precursor is the neurotransmitter serotonin, which is a major player in uplifting your mood.

It is not surprising, then, that chronic light pollution might not only wreak havoc on your sleep, but also cause you to awaken as a grumpy, blurry-eyed, green faced ogre in the morning. Like serotonin, melatonin plays important roles in your physical and mental health. Studies have shown that insufficient melatonin production can set you up for:

• Decreased immune function
• Accelerated cancer cell proliferation and tumor growth (including leukemia)
• Blood pressure instability
• Decreased free radical scavenging
• Increased plaques in the brain, like those seen with Alzheimer’s disease
• Increased risk of osteoporosis
• Diabetic microangiopathy (capillary damage)

Not getting enough sleep may even accelerate aging and shorten your lifespan.

Melatonin and Depression

There are many studies that suggest melatonin levels control mood-related symptoms, such as those associated with depression -- especially winter depression (aka, seasonal affective disorder, or SAD).

In a study published in May 2006, researchers at the Oregon Health and Science University (OHSU) found that melatonin relieved SAD. 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, or by taking a melatonin supplement at a certain time of day, and the details of the treatment depend on exactly HOW the person is out of phase.

A more recent study (June 2010) about melatonin and circadian phase misalignment found a correlation between circadian misalignment and severity of depression symptoms.

Studies have also linked low melatonin levels to depression in a variety of populations, including multiple sclerosis patients and post-menopausal women. Clearly, anything that negatively effects melatonin production is likely to have a detrimental effect on your mood, which is borne out in the research.

Your Internal Timekeeper

Your internal biological clock is what tells you when it’s time to wake up or go to sleep, but this inner timekeeper is actually controlled by light and dark.

Inside your hypothalamus is a group of cells called the Suprachiasmatic Nucleus (SCN), which controls your biological clock by responding to light. Light reaches your SCN via your eye’s optic nerve, where it tells your biological clock it’s time to wake up. Light also causes your SCN to initiate other processes associated with being awake, such as raising your body temperature and producing hormones, like cortisol.

On the flip side, the lack of light reaching your SCN triggers melatonin production, which helps you sleep -- and this is why sleeping in total darkness is so important.

Having a light on at night squelches the production of melatonin, which is thought to be the reason for the hypothalamic changes discovered in the Ohio State study above. In addition to dampening your mood, a confused body clock can result in increased appetite and unwanted weight gain.

Conducting a Light Check in Your Bedroom

Sleeping in a pitch-black bedroom is an important and relatively easy lifestyle choice to make for your health. Even the dim glow from your clock radio could be interfering with your ability to sleep -- and more importantly, your long term health and risk of developing cancer or major depression.

Personally, I sleep in a room that is so dark that I can’t see my hand in front of my face. 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
• 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

If possible, avoid working the night shift.

Working nights has been linked to significantly lower levels of serotonin, which has negative effects on your mood. If you currently work nights, I would strongly suggest trying to switch your hours, or at the very least restrict your night shift duty to a couple months at a time. This will at least give your body a chance to readjust in between.

If you are interested in finding more information on this subject, I highly suggest reading Lights Out: Sleep, Sugar, and Survival by T. S. Wiley and Bent Formby. The authors believe it is light, not what we eat or whether we exercise, that causes obesity, diabetes, heart disease and cancer. I think there are many other factors contributing to these health problems as well, but impaired sleep is certainly a large contributor.

Now, if it’s been awhile since you’ve had the luxury of gazing up at a truly dark night sky, you might want to plan your next vacation around it. IDA has an inspiring list of vacation spots around the globe, where you might become a stargazing devotee.

A Word to the Wise: Are You REALLY a Night Owl?

You may be wondering what to do if you’re a night person, who simply feels best working and staying awake at night, then sleeping during the day. Day sleeping makes it much more challenging to create a dark environment. My first suggestion is to reconsider whether or not you truly feel better on this schedule, or if it is more a matter of habit. Many people find they can switch back to a more conventional schedule without much difficulty -- and then they are actually surprised by how much better they feel.

If you come to the conclusion that you simply must stay up at night, or if you work the night shift and can’t change it, you can somewhat counter the health effects by keeping to a schedule. By being consistent, your body’s clock will eventually adjust to your sleep/wake cycle, and this is LESS damaging than if you constantly change shifts and expect your body clock to adjust.

When you travel long distances often, have insomnia, or frequently change from day shifts to night shifts, your body has a very hard time adjusting and your health will invariably suffer over time.

Ultimately, your body is a phenomenal source of feedback, and it is important to honor the signals it’s sending you.

What Can We Learn About Sleep From Ayurveda?

Human beings have naturally been sleeping during the nighttime for eons. Coordinating sleep and wake cycles with the Earth’s movement has been an important part of Ayurvedic medicine for over 5,000 years. Ayurveda is a holistic system of healing from ancient India that focuses on maintaining balance of the life energies within us.

What insights might we glean from the ancient science of Ayurveda?

According to Ayurveda, sleep is one of the supporting pillars of life, critical to good health and well-being. Quality sleep acts as a rejuvenator of your mind and body because it enhances Ojas -- the main life-supporting force within your body. According to Ayurveda, insomnia is often caused by being out of sync with nature.

Sound familiar?

Every day the Earth passes twice through Vata, Pitta, and Kapha “phases”, and these phases are believed to have various influences on your quality of sleep:

First Cycle

• 6 am to 10 am = Kapha
• 10 am to 2 pm = Pitta
• 2 pm to 6 pm = Vata

Second Cycle

• 6 pm to 10 pm = Kapha (phase of “heaviness”; BEST for falling asleep)
• 10 pm to 2 am = Pitta (phase of “liveliness and mental alertness”)
• 2 am to 6 am = Vata (phase is “light and airy”; BEST for waking up)

According to Ayurveda, you should go to bed in Kapha time (i.e., before 10 pm) because Kapha has a natural property of “heaviness”, which makes it easier for you to fall asleep.

Many people automatically begin feeling sleepy around 9 pm but fight it, feeling it’s too early to go to bed, and by forcing themselves to stay awake, they miss a valuable window of opportunity for a good night’s rest, caused by Kapha.

From 2 am to 6 am comes the Vatta phase, which is “light and airy.” You may find yourself drifting in and out of sleep, dreaming and wakefulness. This is not the kind of sleep that leaves you feeling refreshed in the morning.

One Ayurvedic practitioner even draws these sleep “equivalents”:

• One hour slept between 9 pm and 12 pm equals three hours’ rest
• One hour slept between 12 pm and 3 am equals 1.3 hours’ rest
• One hour slept between 3 am and 5 am equals one hour’s rest

So, according to Ayurvedic principals if you sleep between 10 pm and 4 am, you are getting the equivalent of 11-12 hours of sleep! Ayurvedic practitioners also recommend the best time for meditation is upon awakening, in the Vata phase of the morning (2 am to 6 am).

Regardless of whether or not you subscribe to Ayurvedic philosophies, getting to bed earlier and arising earlier is a wise choice in terms of natural circadian rhythms. Between that and making your bedroom a DARK sleeping haven, you should be well on your way to getting the best sleep ever!