Sleep has to be at the top of your health priority list if you want to reach your physical, metabolic, and emotional health goals.  I’ve read enough research papers and seen the adverse effects of sleep deficiency in my patients, and more importantly how miraculously they improve in every area of their life when they get more sleep.

If you have children or care about children, be sure to read the end of this post where I talk about the effects of light disorders in children, including the alarming rate of myopia (near-sightedness) that is a threat to vision later in life.

I personally am a different person when I get the sleep I need.  I’m a better father, husband, doctor, writer and lecturer.  I’m more creative, more efficient and far more productive despite trading in an extra hour or two of work for sleep.

In terms of health goals, losing those last few inches or pounds of body fat, dropping your blood glucose levels despite sufficient diet and exercise, reducing your blood pressure, and improving your mood and in many cases reversing depression may be dependent on you getting more sleep and better sleep.

Sleep is a vast topic, but for today’s post I just want to focus on one aspect of our modern lives that is a serious sleep disrupter, and that is light.

Understanding the Natural Effects of Light on Circadian Rhythm

Circadian rhythm refers to the physiological and metabolic processes that are tied to our 24 hour daily biological clock.  There are multiple hormonal processes that are dependent on our daily biorhythms, but right now I want to just focus on melatonin with a few words on cortisol as well.

Melatonin is our natural sleep hormone produced by a structure in our brain called the pineal gland, and its release is dependent upon the interaction of our eyes with light.  Think of melatonin as our “mellow hormone” that helps us mellow out so we can fall asleep.  In our natural environment, when we awake and our eyes welcome the first rays of sunlight, a signal is sent via our retina (a membrane layer at the back of our eyeball that sends nerve signals to the brain) to the pineal gland that suppresses the release of melatonin.  This is a good thing since we want our body to produce less sleep-inducing melatonin, so we feel awake during the day.

When we wake in the morning our body also pulses out the stress hormone cortisol which is  intended to energize us during the day.

One key point I want you to remember is that cortisol is inversely proportional to melatonin, so when our body gets a natural surge of cortisol in the morning, that along with sunlight exposure will reduce melatonin release.

Cortisol is often maligned since it’s referred to as the stress hormone that can make you fat, but we need it to surge in the morning to make us feel awake and alert.  It’s our internal hormonal shot of espresso which is delivered at the right dose and right time when our circadian rhythm is functioning properly.

The opposite effect happens at night.  As the sun sets and our eyes are exposed to less light, a signal is sent via the retina to the pineal gland to stimulate the release of melatonin, which promotes sleepiness.

You don’t need to rush to the local drug store to pick up artificial melatonin supplements to benefit from this effect. It is much better (and cheaper!) to simply limit light exposure to your eyes, so your brain pulses out its own natural supply of melatonin.

Recall I told you that there is a surge of cortisol in the morning (our stress hormone) which promotes wakefulness. In the evening, cortisol dips down (unless you are in a high stress state) and since I told you cortisol is inversely proportional to melatonin, this also facilitates the release of melatonin.  Let’s summarize all this so it’s clear:


Daylight exposure to your eyes–>suppress melatonin–>promote wakefulness

Morning surge in cortisol–>suppress melatonin–>promote wakefulness


Darkness–>stimulate melatonin release–>promote sleepiness

Natural drop in cortisol (in absence of stress)–>increase melatonin–>promote sleepiness

Effects of Modern Life

Everything we described so far is in our natural environment.  What happens if you wake up indoors, sit in your car, and go straight to the office with little to no sunlight exposure, and then return home at night where you spend most of your evening on artificially lit screens?

You are essentially reversing the natural rhythms of your body (and the processes I outlined in the prior section), which in turn completely disrupts the normal hormonal patterns essential for growth, metabolism, and optimal overall health.

When hormones are shifted out of their natural rhythms, disease in some form frequently occurs.  One of the occupations that suffers the most dramatic reversal of natural circadian rhythm are night shift workers.

Night shift workers have a higher risk of conditions like diabetes, heart disease, depression and cancer.  The link between night shift work and cancer is so powerful that the WHO (World Health Organization) has classified night shift work as a probable carcinogen. Women who work the night shift for years have a higher risk of breast cancer.

Even if you are not a night shift worker, staying up long nights on your screens and devices can interrupt your body’s natural hormone patterns, putting you at risk for disease.  Keep in mind that when it comes to diseases like heart disease and cancer, often it’s a combination of factors that cumulatively increase risk.

For example, if you have insulin resistance (prediabetes, diabetes, etc.) and a disrupted sleep cycle, those together can significantly raise heart disease and cancer risk.  Read this post which explains how insulin resistance and blood glucose abnormalities are tied to cancer risk.

Effects of Blue Light on Melatonin

The most compelling recent studies on sleep are the ones that show what a powerful impact even small amounts of blue light emitted from screens can have on sleep.  Blue light is emitted from most common household devices like TVs, computers, laptops, smart phones, tablets, fluorescent and LED lighting.

Compared to other colors on the spectrum, blue light is short wave-length and high energy so it is a potent suppressor of sleep-inducing melatonin.

As a result, studies show blue light exposure prior to bedtime increases the time it takes to fall asleep due to heightened alertness.  Blue light exposure also impairs sleep quality by reducing REM sleep (aka dream sleep) and deep phase sleep, which in turn make it more difficult to wake up.

Even if your sleep duration is adequate, the quality and depth of sleep may be suffering from the effects of blue light exposure.  This explains why you might feel like a zombie despite sleeping through the night.

How to Fix Your Light Issues

To get your circadian rhythm and sleep back on track, you have two essential goals:


Sunlight is your most natural, powerful source of light that can quickly improve your sleep rhythms.  It’s best to get a double dose of sunlight, first upon waking in the morning.  This may mean having breakfast outdoors on the patio or doing morning exercise or a morning walk.  Aim for 30 minutes.

Another key time to get sunlight is around solar noon, which is when the sun is at its highest point in the sky, depending on your location and the time of year.  Use this link to enter your location and determine solar noon where you live.

Right now in San Francisco where I’m writing from, on 3/25/16,  solar noon will be at 1:16p.  You don’t have to be exact, but getting at least 30 minutes of sunlight exposure around solar noon can help train and normalize your biological clock. Again, eating lunch outdoors or walking/exercising during this time would be ideal.

Even if you’re overloaded with work, can you sit outdoors with your phone and/or your laptop, or take a phone call or schedule a walking meeting while catching some sun?

If you live during a season or in a part of the world where natural sunlight is scarce, consider investing in a bright lamp that delivers 10,000 lux units of bright light.  I own this one and use it intermittently in the winter, but there are several brands available.  Getting adequate light exposure at the right dose and right time can help improve mood and energy levels and can also help you make a quick recovery from jet lag.  Read this article for 10 tips on using light therapy.


The sooner you can shut off screens after sunset the better.  I know this is tough, but if you can even set a screen curfew for 8:30 or 9p latest, that would really help.  Remember, this not just about sleep, but about restoring normal hormonal balance and preventing disease.

Screens have a double negative effect on two of the major hormones that influence sleep.  They block melatonin, which also increases the release of cortisol, and they independently increase cortisol since screens are naturally stimulating, which in turn lowers melatonin.  

What if you absolutely must get work done?  There are a few things I recommend:

  1. Filter out blue light.  Lots of options available such as:
  • Download f.lux onto your computers and devices for free.  This will naturally filter out the damaging blue rays from your screen as the sun begins to set with your screen taking on an increasingly amber hue.
  • Download “Night Shift” onto your Iphone which is available with the iOS 9.3 update.  Read about it here.  A company like Apple would not be introducing a standard feature onto their phone unless there was hard evidence that it was causing damage to our health.  This is basically f.lux integrated into your iOS devices.
  • Wear orange goggles like these.
  • There are now clear lenses available to block out blue light.  Check out this site where some of my patients have purchased blue light-blocking, stylish clear eyeglasses for adults and kids.

2. Get enough sunshine during the day.  If you know ahead of time that you will be staying up late to get work done, then be sure to get adequate sun exposure during the day which makes you more resistant to the effects of working at night.

3. Make nighttime work as calming as possible.  If I have to work at night, in addition to using blue light filtering, I also make my work environment very calming.  I play relaxing music in the background, I keep background lights dim to dark, I sip on non-caffeinated herbal tea or some other hot beverage, and I am especially mindful of my breathing…taking slow deep breaths whenever possible.

4. Early morning work instead?  Even if you have a deadline to catch, is it possible to work just a little later at night and get up early to finish your work rather than working until the wee hours?  This would be better since your body expects to get light exposure when you wake up, so you can use your screen as a substitute.  Better to get early morning screen light exposure rather than getting it late at night.

I use the same philosophy for entertainment.  If you are dying to watch a recording of a sporting event, TV show, etc., it’s better you watch it early in the morning…perhaps while exercising instead of late at night.

5. Morning exercise helps your circadian rhythm.  If you have sleep issues, morning exercise is generally preferred to maintain your sleep rhythm. Even if you don’t have time to hit the gym, try some form of exercise or activity.  This could be yoga, body weight exercises or a 20-30 minute walk, ideally in sunlight.

Perhaps you can get to work a bit early and take a brisk walk around campus before you settle into your office?  It’s not only an energizing way to start the work day, but can have great downstream benefits when you sleep that night.

Exercise is a powerful tool to help you sleep better since muscular exhaustion and improved aerobic endurance help you get more of the rejuvenating deep phase sleep.  Read my popular 2-part series on exercise here which will help improve energy, fitness and sleep.

6. Don’t forget about other sleep factors.  Remember I mentioned at the beginning of the post how I’m only focusing on the effects of light on sleep.  There are multiple other factors.

If you are physically inactive, experience chronic stress, sleep on an uncomfortable mattress in an overheated room (cooler is better), drink too much caffeine especially late in the day, etc., then simply downloading f.lux, night shift or wearing blue light-blocking glasses may do little or nothing to improve your sleep.  

Sleep-disordered breathing is another major issue that influences sleep and I recently read this wonderful book which taught me a ton on this topic in addition to a comprehensive approach to sleep.  I’ll feature this in a future post.  If fatigue is a persistent issue, read my post here and download the free e-book.

How to Fix Your Stress Issues

Although this post is focused on the impact of disrupted light patterns, chronic stress continues to be the primary cause for disrupted sleep in most of my patients.  Please be sure to check out my comprehensive list of tools and resources here, including my favorite Apps, to help manage stress.

Optimizing lighting without managing chronic stress and emotional disorders is unlikely to have a significant impact on improving sleep.  Try to manage both simultaneously.

What About Kids?

Kids are susceptible to all the harms of blue light we’ve discussed.  When we talk to smokers in the clinic, we quantify exposure by “pack-years.”  For example, if you smoke a pack a day for 20 years, you are a 20 pack-year smoker.

If we are classifying excess blue light as having a carcinogenic effect, then young kids will be exposed to many more “blue light years” than those of us who adopted this habit later in life.  

This means a longer duration of living with disrupted hormonal patterns from an aberrant circadian rhythm with all its effects on physical and emotional health.  Read this article about the effects of smartphone screens on sleep in children.

Kids also especially rely on the release of growth hormone during deep sleep.

When kids and teens short-change sleep, they short-change growth. 

In our experience in the clinic and in the community we repeatedly see sleep-deprived kids who are short-statured despite having normal to tall parents.  Their modern day sleep patterns are preventing them from achieving their genetic growth potential.   Read more about kid’s sleep here in our blog post.

There is also a shockingly high incidence of myopia (near-sightedness) in Asian children that appears to be linked to a lack of outdoor sunshine with rates between 80-90% in young adults.  The global incidence of myopia has increased overall, with Asians hit the hardest given relatively less time spent outdoors from intensive academic pressure.

Sunshine stimulates the production of vitamin D (read about vitamin D deficiency here) and the release of the neurotransmitter dopamine which may have a protective effect on the lens to prevent the early onset myopia.  Read this CNN report for details.  Myopia from an early age can set the stage for more damaging eye conditions later in life like glaucoma, cataracts and retinal detachment which can lead to vision loss and blindness.

I want to summarize what I’ve told you so far.  A dearth of sunshine during the day and an abundance of nocturnal screen light can increase the risk of chronic health conditions like diabetes, heart disease, cancer, depression and visual deterioration in children and adults.

I know it’s hard to fathom that staring at a small or large blue screen at night for prolonged periods of time is enough to trigger disease, but there is now overwhelming evidence to support this.

What has become a normal part of life is anything but normal, and it is up to you as a parent to protect your children from something so serious that can be prevented with something so simple…spend just a little more time in the sun and shut screens off at least 90 minutes before bedtime.  Kids and teens cannot be expected to do this on their own…they’re addicted just like many of us, so you may have to enforce some serious household rules (setting screen curfews, etc.) for the health of the entire family.

Do you have any suggestions or practical tips on fixing our modern day light issues?  If so, do share.  In the mean time, I wish you all abundant sunlit days and darker nights.  Have a good night!