The Dangers of Leaving the Light On

Study finds that exposure to room light suppresses melatonin production and may lead to health complications

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Keeping the lights on before going to sleep may have a negative influence on your health, according to a study to be published in the Journal of Clinical Endocrinology & Metabolism.

A team of researchers found that exposure to indoor light between sunset and bedtime has a significant effect on melatonin levels, which consequently can affect those processes controlled by melatonin, including sleepiness, thermoregulation, blood pressure, and stable glucose levels.

According to Joshua Gooley, Ph.D., of Brigham and Women's Hospital and Harvard Medical School, and lead author of the study, it is a common practice for people to leave the lights on before and during the usual hours of sleep. In those same hours, people also frequently are exposed to electrical light because of evening work or social activities. The study's findings, says Gooley, demonstrate the adverse effects that electrical lights can have on sleep quality as a result of the suppression of melatonin.

Melatonin is a hormone produced by the pineal gland that regulates sleep cycles. The hormone is also known to lower blood pressure and body temperature. In recent years, researchers have investigated melatonin's potential as a treatment for insomnia, hypertension, and cancer.

In order to determine the effects of indoor light on melatonin production, researchers exposed 116 volunteers to either room light or dim light in the eight hours leading up to bedtime. The volunteers, ranging from 18 to 30 years of age, underwent this exposure for five days in a row. Results from frequent blood plasma samples showed that, compared to exposure to dim light, exposure to room light before bedtime reduced melatonin production by approximately 90 minutes. The researchers also found that exposure to room light during normal sleep hours can cut melatonin production by more than half.

Other researchers have hypothesized that melatonin suppression can lead to more serious health complications such as cancer and type 2 diabetes. As such, the results of this study highlight the health risks to which some people are vulnerable after years of exposure to indoor light. Future research should focus on other risk factors presented by the suppression of melatonin, says Gooley.

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Review Date: 
January 16, 2011
Last Updated:
January 17, 2011