A new study explores the potential link between artificial night lighting that interrupts sleep—from blue-light wavelengths emanating from digital devices to light-emitting diode (LED) street lights in major cities—and the potential for increased risk for some cancers.
Published in Environmental Health Perspectives in April, the Spain-based study looked at the link between exposure to artificial light at night (ALAN) and risk for prostate and breast cancers. For the study, researchers analyzed two sets of data: 1) blue-light sensitive images taken from the International Space Station of Barcelona and Madrid at night and 2) questionnaires sent to about 4,000 people, including participants with cancer, plus a control group. Indoor ALAN was gathered from the questionnaires; outdoor ALAN from the images.
Study participants subjected to higher levels of blue light (lights on during sleep cycles) had 1.5 times higher risk for developing breast cancer and two-fold higher risk of developing prostate cancer compared to people who had less exposure to artificial light, the study researchers say.
"Findings from this large case-control study of two cancers that have been associated with circadian disruption and light at night during shift work provide some support for the influence of ALAN for the development of cancer in the general population," concluded an international team of researchers at the Barcelona Institute for Global Health. "Men who reported the highest level of exposure to indoor ALAN were at greater risk of prostate cancer than men who reported no indoor illumination at night.
"Although both cancers were less likely among those in the highest versus lowest tertile of exposure to outdoor ALAN in the visible spectrum, outdoor ALAN in the blue-light spectrum, which is believed to be the most biologically relevant exposure, was positively associated with prostate cancer and, to a lesser extent, with breast cancer," they add.
What doctors of optometry should know
Karl Citek, O.D., Ph.D., is chair of the AOA's Commission on Ophthalmic Standards, as well as subcommittee chair for the American National Standards Institute (ANSI), which sets consumer-protection standards for the manufacture of sunglasses and over-the-counter reading glasses.
After reviewing the study, Dr. Citek's takeaway was that the increases posed minimal risks to most people.
"Most of us do not need to make major lifestyle changes nor worry much about the reported findings," says Dr. Citek, a professor of optometry at Pacific University College of Optometry. "Increased exposure at night to light—especially blue light—can disrupt melatonin release, which has been linked to circadian rhythm disruption and higher incidences of certain types of cancer. This study concentrated on breast and prostate cancers, and it did consider other factors in addition to exposure to artificial light (e.g., tobacco use, body mass index, family history).
"Nonetheless, the only truly significant danger—more so for prostate than breast cancer—may result with high-level exposure to artificial light at night, such as sleeping in a room with the lights fully on," he says. "Bottom line: Sleeping, especially for men, should occur in a room with no more than dim light."
5 tips for alleviating digital eyestrain
Doctors of optometry should continue to educate patients about blue light and its impact on vision and health, recommending patients:
- Power down before turning in. As hard as it may be, turn devices off at least one hour before bedtime as part of your evening routine. High-energy visible light can potentially upset normal circadian rhythms that lead to a good night's sleep by suppressing those melatonin levels at night.
- Mind the 20-20-20 rule. When working with digital devices for a prolonged period of time, it's appropriate to take a 20-second break every 20 minutes to focus on something 20 feet away. These regular breaks can help alleviate digital eyestrain.
- Keep their distance. In addition to following the 20-20-20 rule, it's also appropriate to maintain a comfortable working distance from your digital device. Find a comfortable distance from your screen where text is easily readable, while your back, shoulders and head can maintain an upright posture. Generally, the preferred viewing distance is between 20 and 28 inches from eyes to screen.
- Make adjustments. Consider adjusting screen height or text size. Keep computer screens about four to five inches below eye level from the screen's center. The AOA recommends reducing the glare by adjusting device settings or using a glare filter to decrease the amount of blue light reflected from the screen.
- Keep those eyes healthy. Schedule regular, comprehensive eye examinations with your doctor of optometry to detect and address vision problems.
Doctors of optometry say recommendation for screenings in primary care offices casts doubt and clouds public awareness.