The link between nighttime light and your thyroid

Due to the rapid growth of electric lighting over the past century, nightscapes in towns and cities have changed dramatically. We’ve become accustomed to using lights at any time of night, and in many cities, it’s so light outside at night that it’s difficult to see the stars.

This convenience comes with a lot of negative health effects. Research on exposure to artificial light at night suggests it can increase risks for obesity, depression, sleep disorders, breast cancer and diabetes, among other illnesses. Now, another potential risk can be added to that list….

Thyroid cancer and night light

An observational study has found a possible connection between high levels of outdoor artificial light at night and a higher risk of thyroid cancer. This is in line with the association between higher levels of nighttime light and an elevated breast cancer risk, since some breast cancers may share a common hormone-dependent basis with thyroid cancer.

Researchers looked for a connection between light at night and later development of thyroid cancer among participants in the 1995-96 NIH-AARP Diet and Health Study, which recruited American adults ages 50 to 71. They analyzed data from satellite images to estimate levels of night light at participants’ residential addresses, then identified thyroid cancer diagnoses through 2011 using state cancer registry databases.

Among the 464,371 participants who were followed for an average of 12.8 years, 856 cases of thyroid cancer were diagnosed — 384 in men and 472 in women. Here’s what they found…

  • The highest quintile of light at night was linked with a 55 percent higher risk of developing thyroid cancer compared with the lowest quintile.
  • This association was stronger in women than in men and was mainly driven by the most common form of thyroid cancer, papillary thyroid cancer.
  • In women, the association was stronger for localized cancer that had not spread to other parts of the body, while in men the association was stronger for more advanced stages of cancer.
  • Association was similar across tumor size, sociodemographic characteristics and body mass index.

According to the researchers, additional epidemiologic studies are needed to confirm their findings. If confirmed, it will then be important to understand the underlying mechanisms of the relationship between light at night and thyroid cancer.

For instance, night light may disrupt the body’s circadian rhythms, a risk factor for various types of cancer. And light at night suppresses melatonin, an antioxidant and estrogen modulator that may have important antitumor effects. Melatonin also induces sleep, strengthens the immune system, lowers cholesterol and supports the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands.

“As an observational study, our study is not designed to establish causality,” says Dr. Qian Xiao of The University of Texas Health Science Center at Houston School of Public Health. “Therefore, we don’t know if higher levels of outdoor light at night lead to an elevated risk for thyroid cancer; however, given the well-established evidence supporting a role of light exposure at night and circadian disruption, we hope our study will motivate researchers to further examine the relationship between light at night and cancer and other diseases.

“Recently, there have been efforts in some cities to reduce light pollution, and we believe future studies should evaluate if and to what degree such efforts impact human health,” Dr. Xiao adds.

Controlling light use at night

It’s not realistic to completely stop all use of artificial light at night, and you certainly can’t control the amount of artificial light used outside your home. But there are steps you can take to better control your own night light use.

Block the blue: Researchers find that exposure to blue light at night is especially harmful to our health. Unfortunately, blue light is everywhere, from energy-efficient LED and compact fluorescent lightbulbs to computer screens, TVs, mobile phones and other electronic displays.

The American Medical Association recommends shielding all of your outdoor light fixtures and only using lighting with 3000K color temperature and below, such as a bulb that produces a soft, warm white or yellowish light. You can purchase LED bulbs at this color temperature or use incandescent bulbs. At the very least, make sure your bedroom lights have this type of bulb to encourage healthier sleep.

As for electronics, you can use an app that filters the blue light at night, turning it into a less harmful warm, yellow light. Most computers and smartphones are now equipped with this function, but if yours is not, you can download F.lux, Lux or Twilight for your device.

Another way to combat the blue light emitted by TVs or devices is to wear glasses designed to filter it out. You can find a list of some of the best blue-light blocking glasses here.

Keep outdoor light outside: If you live in an area with a lot of outdoor lights, you’ll want to take steps to block that light from shining inside your home and disturbing your nights. Blackout curtains are one solution, as are thick window shades or exterior shutters. Make sure the curtains or shades you install are the proper size to completely cover the window so that they eliminate as much outside light as possible.

If installing blackout curtains, shades or exterior shutters is not an option, you can try using a sleep mask at bedtime to keep the outside light from disturbing your sleep. Pick a sleep mask that fits tightly enough to block out all light while still being comfortable enough for you to sleep in.

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Study Links Exposure to Nighttime Artificial Lights with Elevated Thyroid Cancer Risk — Wiley

Human Health — International Dark-Sky Association

What does 3000k, 4000k, 6000k LED Bulbs mean? — RG Alternatives

Ways to Block Outside Lighting — SFGate

Carolyn Gretton

By Carolyn Gretton

Carolyn Gretton is a freelance writer based in New Haven, CT who specializes in all aspects of health and wellness and is passionate about discovering the latest health breakthroughs and sharing them with others. She has worked with a wide range of companies in the alternative health space and has written for online and print publications like Dow Jones Newswires and the Philadelphia Inquirer.