The Effects of Artificial Lighting on Melatonin

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Research recently published in the Journal of Clinical Endocrinology & Metabolism indicates that keeping the lights on in the period between dusk and bedtime strongly suppresses the production of the hormone melatonin, and may potentially interfere with related processes such as sleepiness, blood pressure, blood glucose control, and temperature regulation.

Melatonin production, which occurs in the pineal gland in the brain, is stimulated by darkness and inhibited by light. The hormone is involved in maintaining the sleep–wake cycle and lowering blood pressure and body temperature; research also suggests that melatonin may affect blood glucose levels and indicates that melatonin receptor genes are linked to Type 2 diabetes. Supplements of melatonin have been explored as a treatment for a variety of conditions, including insomnia, high blood pressure, and certain types of cancer.


To determine whether exposure to artificial room lighting in the late evening could be interfering with melatonin production, researchers recruited 116 healthy volunteers, ages 18 to 30, who were exposed to either standard room lighting or dim lighting in the eight hours before bedtime for five consecutive days. Blood samples were collected from an intravenous catheter in the participants’ forearms every 30 to 60 minutes to check melatonin levels.

The researchers found that exposure to standard room lighting before bed shortened the duration of melatonin’s presence in the blood by about 90 minutes compared to exposure to dim lighting. Moreover, lights left on in the room during sleep reduced melatonin production by more than 50%.

Lead study author Joshua Gooley, PhD, of Brigham and Women’s Hospital and Harvard Medical School, noted that “On a daily basis, millions of people choose to keep the lights on prior to bedtime and during the usual hours of sleep. 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.”

Further studies, Gooley says, are required to determine how melatonin is involved in regulating glucose metabolism.

To learn more about the research, read the article “Room Light Before Bedtime May Impact Sleep Quality, Blood Pressure, and Diabetes Risk” or see the study’s abstract in the Journal of Clinical Endocrinology and Metabolism.

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