Dr. John Day, Cardiologist

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Does Artificial Light Cause Cancer?

A recent Harvard study reported that artificial light at night increases your risk of cancer by up to 21%.  In this article, I discuss how artificial light at night might cause cancer and what you can do to eliminate this risk.

Mary’s Experience

Mary had no choice but to work the graveyard shift.  She was a nurse and shared childcare duties with her husband.

As he worked days and she worked nights, they always had one parent there for their children.  Even though she rarely saw her husband at least, they could save on daycare.

This arrangement seemed to work for them until Mary hit her 40s.  At age 43 she started developing heart arrhythmias, and by 46 she was diagnosed with breast cancer.

For someone who was otherwise healthy and worked out regularly, this seemed like too much of a coincidence.  At Mary’s last visit with me, she asked, “Do you think working nights caused my heart problem and cancer?”

“Possibly.  Is there any chance you could switch to days?” I asked.

“I have enough seniority at my hospital so it shouldn’t be too hard,” she said.

The Harvard Artificial Light and Cancer Study

To better understand the potential cancer risks of artificial light, in this study Harvard researchers followed 109,672 female nurses for 24 years.  To determine how much exposure these nurses had to artificial lights for 24 years, researchers studied nighttime satellite images of their houses and neighborhoods.  Once they knew their artificial light exposure, they could then see if there was a link between artificial light at night and breast cancer risk.

In addition to looking at how bright their homes were on satellite images, they also factored in other things like working nights, smoking status, and other health and lifestyle factors.  As you might have suspected, the more the artificial light at night, there was the higher the risk of breast cancer.  Fortunately, for women with healthy lifestyles, this increased breast cancer risk was only 7%.  However, in smokers and nurses working nights, the increased cancer risk from artificial lights was as high as 21%.

How Could Artificial Lights at Night Cause Cancer?

Was the methodology used in this study perfect?  Of course not.  For example, nighttime satellite images can’t perfectly calculate their exposure to artificial light at night.  For example, the satellite images would never have been able to pick up bright lights inside of their homes if they had great window shades.

However, before you discount this study, it is important to remember that this is not the first study to link artificial lights at night to cancer.  Indeed, there have been many published studies showing this association.

Although this study was in women, men also seem to be at risk.  For example, studies show that artificial lights at night also increase the possibility of prostate cancer.

The reason why artificial light at night may cause cancer is likely due to shutting down natural melatonin production in the body.  As a result, blue light at night disrupts natural circadian rhythms, sleep, and hormonal balance. Thus, the hormonally triggered cancers, like breast and prostate cancer, seem to be especially susceptible to nighttime blue light exposure.  Certainly, one unanswered question from the medical literature is whether melatonin supplements could undo the risk of artificial light at night.

What is Blue Light?

Blue light has a very short wavelength.  With this short wavelength, it also produces a higher amount of energy.

While blue light is good during the day as it boosts your energy, attention, reaction times, and mood at night it can be very disruptive. As blue light shuts down your natural melatonin production, your sleep may be less than ideal.

What Are the Risks of LED Lights?

While LED lights are brighter and more energy efficient, there is a downside.  The problem is that these artificial lights emit more blue light than what you see with traditional lighting.  If you are going to use LED lighting in your house, you may want to consider a dimmer switch on every light for nighttime use.

What Are the Risks of Blue Light at Night?

In addition to the cancer risk that we have already discussed, there are many additional risks of artificial lights at night.  Here are some that are well backed up by many medical studies.

1. Blue light disrupts your circadian rhythm and makes it hard to sleep

If you want to compromise your sleep, then blue light at night is your answer.  Indeed, even small amounts of blue light before bed have been shown to shift your circadian rhythm to a later time.

Because of the impact blue light has on sleep times, many scienticists now believe that there may be no such thing as a “night owl.”  Rather, so called “night owls” may just be more sensitive to blue light than everyone else.  This would explain why studies show that if you remove all artificial light from night owls that they quickly synchronize their sleep and wake times with the sun.

Thus, night owls become larks naturally if you remove all artificial lights at night.

2. Obesity

Darkness triggers leptin production in our bodies.  Leptin is what makes us feel full.  As long as artificial lights are on at night, you may get the signal to eat. Perhaps this explains why so many people feel compelled to snack before going to bed.

3. Heart Attacks

As we have covered in previous articles, anything that disrupts your circadian rhythm could increase your risk of a heart attack.  Studies show that even just losing one hour of sleep from daylight savings time puts you at risk of a heart attack.

4. Diabetes

In addition to making you want to eat more, studies show that circadian rhythm disruption may make you insulin resistant.  In other words, the natural insulin your pancreas makes when you eat carbohydrates no longer has any effect.  As a result blood sugar levels rise and diabetes ensues.

Practical Tips

1. Get as much natural light during the day as possible.

Natural sunlight packs blue light.  Get as much of this as you can during the day.  Even getting outside during your lunch hour on a cloudy day will expose you to far more blue light than even the brightest of indoor lights.

2. Don’t look at electronic screens after dinner.

Indoor lights and electronic screen time are responsible for much of the sleep deprivation that is so common with modern life.  If you can avoid electronic screens from TVs, phones, or computers at night, then your sleep and health will likely improve.  If you absolutely must use an electronic device at night, then use an app to block blue light from your screen or wear glasses that block the blue light.

3. Minimize artificial lights at night

Keep the lights in your house as dim as it is safely possible at night.  Consider warmer lights similar to what you might get from a candle at night.  When it comes to circadian rhythm disruption, red light is least likely to cause harm.

4. Don’t fight the sun

Probably the most important tip is to live in your natural circadian rhythm.  Don’t fight the sun.  Get up when the sun rises in the morning and start preparing for bed soon after the sun sets in the evening.

If you have to work nights, then do the opposite.  Try to keep things as bright as you possibly can at night and then as dark as possible during the day.  While this may help, you are still putting yourself at risk of a heart attack or cancer.  To eliminate this increased risk, you will need to work days as soon as it makes sense for you financially.

How do artificial lights at night affect you?  Please leave your comments on this article below.   Also, if you enjoyed this article, please be sure to sign up for my free weekly newsletter, podcast, or pick up a copy of our new book, The Longevity Plan.