Light Exposure May Cut Production of Melatonin
Study Shows Artificial Light Before Bedtime May Affect Quality of Sleep
By Bill Hendrick
WebMD Health News
Reviewed by Laura J. Martin, MD
woman asleep with lamp on

Jan. 19, 2011 -- Exposure to artificial light after dusk and before bedtime may reduce sleep quality by suppressing production of the hormone melatonin and may also have other negative health effects, according to a new study.

Melatonin, produced by the brain’s pineal gland at night, regulates the sleep-wake cycle. It also has been shown to lower blood pressure and body temperature, says study researcher Joshua Gooley, PhD, of Brigham and Women’s Hospital and Harvard Medical School in Boston.

“On a daily basis, millions of people choose to keep lights on prior to bedtime and during the usual hours of sleep,” Gooley says in a news release. “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.”

In the study, Gooley and colleagues evaluated 116 healthy volunteers between the ages of 18 and 30 who were exposed to room light or dim light in the eight hours prior to bedtime for five straight days.

Blood plasma was collected every 30 to 60 minutes via an intravenous catheter in the forearms of volunteers so that melatonin measurements could be taken.

A Visual Guide to Sleep Disorders
Artificial Light and Health

Results were clear, showing that exposure to room light before bedtime shortened melatonin duration by about 90 minutes, compared to dim light exposure. In addition, the researchers say, exposure to room light during the usual hours of sleep suppressed melatonin levels by more than 50%.

“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,” Gooley says.

He adds that in future studies it will be important to determine in more detail the health impacts resulting from chronic nighttime exposure to electrical lighting on melatonin suppression.

Researchers Charles Czeisler, MD, PhD, FRCP, also of Brigham and Women’s and Harvard, discloses receipt of financial support from pharmaceutical companies and holds patents for sleep-related devices.

Steven W. Lockley, PhD, reports receiving honoraria or travel support from lighting companies and other concerns related to sleep research. He also has received an advance from Oxford University Press for a book he is writing on sleep.

The study is set to be published in March in the Journal of Clinical Endocrinology & Metabolism.