A study published in 2023 found that wearing an eye mask to block light while sleeping overnight in the home improves memory and alertness the next day. That should help with driving, learning, and other important activities5.
The new research did not evaluate why the eye mask was so beneficial, but previous research shows that sleeping in total darkness allows your body to produce as much of the hormone melatonin as possible. This is good because when your production of melatonin drops, you are at greater risk of breast and/or colorectal cancer and other health risks.
What is Melatonin?
Melatonin is a hormone that is naturally produced in your body. It is secreted by the pineal gland, which is buried deep in the brain. Melatonin is only produced at night and only when it is dark, which means that melatonin production peaks between 3:00 a.m. and 5:00 a.m. for most people. This hormone helps to regulate your circadian rhythm, which is like your body’s natural clock. When melatonin and several other chemicals are released, you feel drowsy and your body temperature lowers. In addition to this sleep-cycle function, melatonin also works as an antioxidant. This means that it can help prevent damage to your DNA that can result from aging, exposure to cancer-causing chemicals, or harmful rays from the sun. Preventing damage to DNA is important because DNA damage can cause cancer.
Doesn’t My Body Produce Enough Melatonin?
There have been major advancements in technology over the last two centuries, one being the light bulb. Because of the light bulb (and electricity, in general), we are able to stay awake and active much later, so the night is not as dark as it used to be. Think of New York City: the city that never sleeps. Cities are so lit up at night that it can be hard to see the stars. This is referred to as “light pollution.” And, of course, even in the middle of nowhere, you can keep your lights on all night in your house.
Our ability to turn night into day has allowed for more night shift work, often called “the graveyard shift.” Even if you don’t work on the late shift, you may be working at home late at night or staying up late watching TV or using the internet. Unfortunately, this kind of schedule has many effects on your body, including reducing the amount of melatonin produced. But it is not just night owls or shift workers who suffer from a decreased production of melatonin. Sleep studies show that almost everyone wakes up at some point during the night, even if we do not remember it. Unless you have blackout shades on your windows, there is a good chance that some light is coming into your bedroom and that your eyes are registering this light during those wakeful periods.[2]
New technology is compounding the effects of light pollution. Early incandescent light bulbs that were dim and yellow and did not affect melatonin production very much. Now, artificial light emits more blue wavelengths. For example “Cool White” fluorescent bulbs are a very popular choice of light bulb because they are bright, moderately energy efficient, and relatively inexpensive. They also produce a lot of blue light which is why they have a “cool” effect. Maybe you have noticed while driving that certain people’s headlights appear to be very bright and have a blue tint to them. These new headlights produce blue wavelengths of light. Unfortunately, research shows that blue wavelengths of light are especially effective at reducing melatonin production in humans.[3] All types of computer monitors and television screens also emit blue light.
Why Is Having Less Melatonin A Bad Thing?
Believe it or not, the International Agency for Research on Cancer (IRAC) classified shift work as a probable human carcinogen in 2007. There have been numerous studies showing a link between night shift work and an increased incidence of breast cancer. For instance, a 2003 study done in the Netherlands found that by working half a year at night, a person’s risk of breast cancer increased 150%.[3] This major study found that nurses who worked night shifts at least 3 times a month for 15 years or more had a 35% increased risk of colorectal cancer.[3] If you’re still unconvinced, a 2009 study conducted in 147 communities in Israel found that women who lived in neighborhoods where it was bright enough to read a book outside at midnight had a 73% higher risk of developing breast cancer than women living in areas without outdoor lighting.[2]
What Can I Do To Limit My Chances Of Getting Cancer Because of Light At Night?
The good news is that there are easy and inexpensive ways to limit the amount of light you are exposed to at night. For starters, if you have electronic appliances in your bedroom that produce light (like a clock radio or cable box), pick those that have red lights as opposed to green or blue lights. Walmart, Target, Best Buy, and many other stores all carry alarm clocks and radios that display the time in red numbers. These brands are not more expensive than their blue numbered counter-parts. Studies show that red lights don’t cause as much of a decrease in the amount of melatonin produced by your body.[4] Also, if you have a television or computer in your bedroom, turn it off before you go to sleep.
It is also a good idea to limit the amount of time you spend in front of a screen at night. If you spend a few hours a night in front of your computer, whether or not you’re not in your bedroom, you are decreasing the amount of melatonin that is being produced in your brain. Most screens today offer a “night mode” which reduces the amount of blue light used and creates an orange tint. This is a recommended setting to use before bed.
Also, since melatonin production is highest between the hours of 3:00 am and 5:00 am, make sure you’re in bed and asleep by 3:00 a.m., and if at all possible, sleep until at least 5:00 am. While you probably will not be able to petition your community to get the street light in front of your house turned off, you can buy blackout shades to block the light. Most department stores sell blackout shades, and they are relatively inexpensive. If you don’t want to invest a penny more in “window treatments,” consider using a sleep mask. Airlines sometimes give them away in travel kits, but you can also buy them online or in a department store. Besides lowering the risk of getting certain cancers, sleep masks can also help you fall asleep faster, have a better night’s sleep, and feel much better the next day. Those are great benefits for such a simple, no-risk strategy.
All articles on our website have been approved by Dr. Diana Zuckerman and other senior staff.
- Navara J, Nelson R. The Dark Side Of Light At Night: Physiological, Epidemiological, and ecological consequences. Journal of Pineal Research. 2007, (43)
- Chepesiuk R. Missing the Dark: Health Effects of Light Pollution. Environmental Health Perspectives. 2009, (117)
- Pauley S. Lighting For The Human Circadian Clock: Recent Research Indicated That Lighting Has Become A Public Health Issue. Medical Hypotheses. 2003
- Reiter R. Circadian Disruption and Cancer: Making the Connection. The New York Academy of Sciences. 2009
- Greco, V., Bergamo, D., Cuoccio, P., Konkoly, K. R., Muñoz Lombardo, K., & Lewis, P. A. (2023). Wearing an eye mask during overnight sleep improves episodic learning and alertness. Sleep, 46(3), zsac305. https://doi.org/10.1093/sleep/zsac305