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.