Why does even subtle light have such a disruptive influence on your sleep/wake cycles? Your body regulates itself via a natural hormone called melatonin that's manufactured in the brain's pineal gland. Melatonin is secreted in the evening, causing sleepiness, and levels stay high throughout the night to keep you asleep. As the sun rises, levels of melatonin decrease sharply to almost zero by 9:00 a.m. When you inadvertently expose yourself to light when you should be sleeping, melatonin production is "switched off." This prods you into alertness when you don't want to be alert—after a 3:00 a.m. bathroom trip, for instance.
While you may wonder why you're wide awake even though you didn't turn on the overhead light in the bathroom, consider all the other sources of light you may have encountered as you stumbled out of bed and toward the toilet-the digital glare of your alarm clock, the cell phone charging on the nightstand, and the nightlight in the hall.
But aside from making it tough to fall back to sleep after waking at night, melatonin-dampening light sources can have a direct effect on your long-term health. Why? Because melatonin has been shown to have antioxidant and anti-cancer properties. In fact, analyses of data from the multiyear Nurses' Healthy Study revealed that women who regularly worked the night shift (where they were exposed to continuous light) had a greater incidence of both breast and colorectal cancer after controlling other factors such as socioeconomic status and lifestyle.
If you're not working the night shift but still have trouble staying asleep, there are small steps you can take toward a darker environment and a more restful slumber:
- Turn lighted alarm clocks away from you, or dim them (many clocks have multiple brightness settings).
- Cover devices that emit light, such as charging cell phones.
- Consider giving up night lights.
- Wear an eye mask to block out light.
- Install blackout shades to keep out light from the street.
Sources:
National Sleep Foundation. "Melatonin and Sleep." Web. www.sleepfoundation.org/article/sleep-topics/melatonin-and-sleep
Schernhammer E S, Laden F, Speizer F E, Willett W C, Hunter D J, Kawachi I, and Colditz G A. "Rotating Night Shifts and Risk of Breast Cancer in Women Participating in the Nurses' Health Study." Journal of the National Cancer Institute 93 (20) (2001): 1563-1568. Web. http://jnci.oxfordjournals.org/content/93/20/1563.full
Schernhammer E S, Laden F, Speizer F E, Willett W C, Hunter D J, Kawachi I, Fuchs C S, and Colditz G A. "Night Shift Work and Risk of Colorectal Cancer in the Nurses' Health Study." Journal of the National Cancer Institute 95 (11) (2003): 825-828. Web. http://jnci.oxfordjournals.org/content/95/11/825.full.
