Other than a cup of coffee right before bed, nothing is more like kryptonite for your sleep than bright blue or white light in the evening. It truly makes you old in several different ways. Blue light is everywhere—we get normal amounts from the sun, but we get large, unbalanced doses from light-emitting diodes (LEDs) used in energy-efficient bulbs and to illuminate the screens on TVs, computers, tablets, and smartphones. Blue light has a short wavelength, so it produces more energy than light frequencies with a longer wavelength, like red light. The odds are high you’ve heard some of this already but dismissed how big of a problem it is on your path to optimal health.

The data is convincing, and it’s easier than you think to transform blue light into only a minor problem. Blue light is not all bad. Exposure to blue light during the day wakes you up, makes you more alert, and can even improve your mood. White- or blue-light emitting goggles and panels are used to treat a number of issues such as seasonal affective disorder (SAD), jet lag, and premenstrual syndrome.1 The problem is that newer artificial lights like LEDs and compact fluorescent light (CFL) bulbs don’t contain most of the infrared, violet, and red light that’s found in sunlight. Instead, they increase the intensity of blue light to a level that our eyes, brains, and bodies haven’t evolved to handle. This is what has come to be known as  “junk light” because it’s just as unhealthy and aging as junk food. You’re bombarded with junk light throughout the day and for much of the night—when you’re on your phone, working at your computer, or watching TV—and all this blue light exposure messes with your sleep.2

Blue light shifts your circadian rhythm in part by suppressing melatonin, the hormone that tells your brain when it’s time to sleep. This tricks your body into thinking it’s daytime 24/7. Normally, the pineal gland, a pea-sized gland in the brain, starts releasing melatonin a couple of hours before it’s time to go to bed. But blue light can mess with this process by stimulating a type of light sensor called intrinsically photosensitive retinal ganglion cells (ipRGCs) in the retina of the eye. These sensors send light information to the circadian clock, telling the body when it’s time to sleep and wake up using more than just melatonin.3 When light sensors are stimulated by blue light at night, you have a harder time falling asleep.

A 2014 study found that people who read from a light-emitting device before bed took longer to fall asleep, slept less deeply, and were more alert than people who read a printed book.4 The amount of blue light you’re exposed to at night has also been linked to rapid aging. The mitochondria in your eyes have to produce a lot more energy than normal to process blue light. When the mitochondria in your eyes are overtaxed, the rest of your mitochondria get stressed, too. This causes metabolic problems and inflammation throughout the body, which of course increases your risk of a premature decline in health.

One study found that adults who were exposed to blue light while eating in the evening had higher glucose levels, slower metabolisms, and more insulin resistance compared to adults who ate in dim light.5 Get some old school low-watt incandescent bulbs, and/or a dimmer swtich to keep the intensity down. It’s way cheaper than diabetes. People exposed to high levels of outdoor blue light at night also have a higher risk of developing breast cancer and prostate cancer, compared to those who had less exposure.6

Other studies have found that a disrupted circadian clock increases your risk of cancer.7 Blue light exposure is also linked to obesity and metabolic disorders, which are both significant risk factors for cardiovascular disease. Blue light can also lead to macular degeneration—damage to the retina that often leads to vision loss.8 More than 11 million people over the age of sixty have some form of macular degeneration, so it’s a significant issue.9

• 1. Robert E. Strong et al., “Narrow-Band Blue-Light Treatment of Seasonal Affective Disorder in Adults and the Influence of Additional Nonseasonal Symptoms,” Depression and Anxiety 26, no. 3 (2009): 273–78, https://doi.org/10.1002/da.20538.

• 2.Gianluca Tosini, Ian Ferguson, and Kazuo Tsubota, “Effects of Blue Light on the Circadian System and Eye Physiology,” Molecular Vision 22 (January 24, 2016): 61–72, https://www.ncbi.nlm.nih.gov/pubmed/26900325; Anne-Marie Chang et al., “Evening Use of Light-Emitting eReaders Negatively Affects Sleep, Circadian Timing, and Next-Morning Alertness,” Proceedings of the National Academy of Sciences of the USA 112, no. 4 (January 27, 2015): 1232–37, https://doi.org/10.1073/pnas.1418490112.

• 3. Tosini, Ferguson, and Tsubota, “Effects.”

• 4. Chang et al., “Evening Use.”

• 5. Karine Spiegel et al., “Effects of Poor and Short Sleep on Glucose Metabolism and Obesity Risk,” Nature Reviews Endocrinology 5, no. 5 (2009): 253–61, https://doi.org/10.1038/nrendo.2009.23.

• 6. Ariadna Garcia-Saenz et al., “Evaluating the Association Between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain (MCC-Spain Study),” Environmental Health Perspectives 126, no. 4 (April 23, 2018): 047011, https://doi.org/10.1289/EHP1837.

• 7. Aziz Sancar et al., “Circadian Clock Control of the Cellular Response to DNA Damage,” FEBS Letters 584, no. 12 (June 18, 2010): 2618–25, https://doi.org/10.1016/j.febslet.2010.03.017.

• 8. .Tosini, Ferguson, and Tsubota, “Effects.”

• 9. .Bright Focus Foundation, “Age-Related Macular Degeneration: Facts and Figures,” last modified January 5, 2016, https://www.brightfocus.org/macular/article/age-related-macular-facts-figures.)