TV Before Bed Does More Than Just Make Us Sleepy in the Morning

Chances are, most Americans choose to wind down before bedtime by watching TV, surfing the Internet, texting their friends, or practically anything involving the light from a lamp.  But that time exposed to electrical light before hopping into bed could be doing more damage than simply cutting in on our sleep time.

According to a recent study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM), exposure to electrical light between dusk and bedtime strongly suppresses melatonin levels and may impact physiologic processes regulated by melatonin signaling, such as sleepiness, thermoregulation, blood pressure and glucose homeostasis.

Melatonin is a hormone produced at night by the pineal gland in the brain. In addition to its role in regulating the sleep-wake cycle, melatonin has been shown to lower blood pressure and body temperature. It has also been explored as a treatment option for insomnia, hypertension and cancer.

In modern society, people are routinely exposed to electrical lighting during evening hours to partake in work, recreational and social activities. This study sought to understand whether exposure to room light in the late evening may inhibit melatonin production.

Joshua Gooley, PhD, of Brigham and Women's Hospital and Harvard Medical School in Boston, Mass. and lead author of the study said millions of people choose to keep the lights on prior to bedtime and during the usual hours of sleep, usually on a daily basis.

"Our study shows that this exposure to indoor light has a strong suppressive effect on the hormone melatonin. This could, in turn, have effects on sleep quality and the body's ability to regulate body temperature, blood pressure and glucose levels," said Gooley.

Along with Gooley, Kyle Chamberlain of the University of Surrey in the United Kingdom; and Kurt Smith, Sat Bir Khalsa, Shantha Rajaratnam, Eliza Van Reen, Jamie Zeitzer, Charles Czeisler and Steven Lockley of Brigham and Women's Hospital and Harvard Medical School in Boston, Mass also worked on the study.

In this study, researchers evaluated 116 healthy volunteers aged 18-30 years who were exposed to room light or dim light in the eight hours preceding bedtime for five consecutive days.

Melatonin levels was measured via intravenous catheters inserted into the forearms of study participants that collected blood every 30 to 60 minutes.

Results showed exposure to room light before bedtime shortened melatonin duration by about 90 minutes when compared to dim light exposure.

Furthermore, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50 percent.

"Given that chronic light suppression of melatonin has been hypothesized to increase relative risk for some types of cancer and that melatonin receptor genes have been linked to type 2 diabetes, our findings could have important health implications for shift workers who are exposed to indoor light at night over the course of many years," said Gooley.

According to Gooley, further research is still needed to both substantiate melatonin suppression as a significant risk factor for breast cancer and determine the mechanisms by which melatonin regulates glucose metabolism.

Until then, these findings make reading by candlelight before hitting the hay seem a little less crazy, no?

Along with Gooley, Kyle Chamberlain of the University of Surrey in the United Kingdom; and Kurt Smith, Sat Bir Khalsa, Shantha Rajaratnam, Eliza Van Reen, Jamie Zeitzer, Charles Czeisler and Steven Lockley of Brigham and Women's Hospital and Harvard Medical School in Boston, Mass also worked on the study.

The article, "Exposure to room light prior to bedtime suppresses melatonin onset and shortens melatonin duration in humans," appears in the March 2011 issue of JCEM.