By Dawn M. Holman, MPH
Behavioral Scientist, Division of Cancer Prevention and Control’s Epidemiology and Applied Research Branch

Photo of Dr. Dawn M. Holman

Sleep. It probably comes as no surprise to you that over one-third of us aren’t getting enough of it. The competing demands of work, family, and social life can make the recommended 7 to 8 hours of shut-eye seem more like a luxury than a necessity. Add in the allure of the many technologies that allow us to connect with each other anytime, anywhere, and it becomes all too easy to skimp on sleep.

What may surprise you is that some of our seemingly harmless nighttime habits may not only be interfering with our sleep, but may also be increasing our risk for a laundry list of chronic diseases, including certain types of cancer. That’s right—cancer. Not usually what comes to mind when we think about getting enough sleep.

Even more intriguing is that our exposure to light during nighttime activities likely plays a role in the link between sleep and cancer. Exposure to light suppresses our bodies’ production of melatonin, a hormone that helps regulate the body’s internal clock (also known as our circadian rhythm). During the day, this is helpful. It boosts our mood and makes us more alert. But at night, it can make falling asleep more difficult and prevents our bodies from producing much-needed melatonin.

A growing body of scientific evidence suggests that regular exposure to light during the nighttime hours may increase a person’s risk for certain types of cancer, including female breast and prostate cancers. Much of this evidence comes from studies of long-term night shift workers, such as nurses and flight attendants, who are often exposed to daytime levels of light throughout their night shifts.

So, for optimal heath, it seems that we need to be getting both enough sleep and enough dark.

If you struggle with getting enough sleep, there are a number of recommendations that might help (often referred to as sleep hygiene). The latest science suggests that reducing your exposure to light at night might also be beneficial. Here are a few tips to consider—

  • Sleep 7 to 8 hours in total darkness.
  • Avoid or minimize use of electronic media with brightly lit screens 2 to 3 hours before going to bed. This includes televisions, computers, and even your smart phone.
  • If you use nightlights, try using dim red lights, which are less likely to suppress melatonin production.
  • Expose yourself to lots of bright light during the day, which will help to reset your body’s internal clock, making it easier to sleep well at night.

As a scientist, it’s humbling to realize how much we still have to learn about cancer. But it can also be empowering to think about what we already know: that we can each take steps to reduce our cancer risk and increase our chances of living a long and healthy life.

National Sleep Awareness Week (March 2–9) has inspired me to take a look at my own nighttime habits. About a year ago, my husband and I installed blackout curtains in our bedroom to reduce our exposure to light while sleeping. But I know there’s more I could be doing. For the month of March, I’m committing to signing off of e-mail and social media by 8 p.m. to give myself time to wind down before bed and further reduce my exposure to light at night.

I challenge you to take a look at your own habits and sleep environment. Pick just one of the tips above and give it a try—even if only for a week. My hope is that we will both see a difference: that we will sleep better, and that with time, “going dark” will become just another one of our healthy habits.

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