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Quote:

From BBC News
January 14, 2020

Melatonin production falls if the lights are on

Having the lights on before bedtime could result in a worse night's sleep, according to a study to be published in the Journal of Endocrinology and Metabolism.
The research shows that the body produces less of the sleep hormone melatonin when exposed to light.

Sleep patterns have been linked to some types of cancer, blood pressure and diabetes.

The US researchers also found lower melatonin levels in shift workers.

Lifestyles may have moved on from a day/night rhythm, but it seems the human body has not.

The pineal gland produces melatonin through the night and starts when darkness falls.

Researchers have shown that switching on lights in the home switches off the hormone's production.

Less melatonin

In the study, 116 people spent five days in room where the amount of light and sleep was controlled. They were awake for 16 hours and asleep for eight hours each day.

Initially the patients were exposed to 16 hours of room light during their waking hours. They were then moved onto eight hours of room light in the morning and eight hours of dim light in the evening.

The researchers found that electrical light between dusk and bedtime strongly suppressed melatonin levels. With dim light, melatonin was produced for 90 minutes more a day.

Dr Joshua Gooley, lead author from Brigham and Women's Hospital and Harvard Medical School, said: "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."

Keeping the lights on through the night also reduced the amount of melatonin produced.

Dr Gooley said: "Given that chronic light suppression of melatonin has been hypothesised 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."

http://www.bbc.co.uk/news/health-12181853

Quote:

Room Light Before Bedtime May Impact Sleep Quality, Blood Pressure and Diabetes Risk

ScienceDaily (Jan. 13, 2011) — 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 and 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.

"On a daily basis, millions of people choose to keep the lights on prior to bedtime and during the usual hours of sleep," said Joshua Gooley, PhD, of Brigham and Women's Hospital and Harvard Medical School in Boston, Mass. and lead author of the study. "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 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. An intravenous catheter was inserted into the forearms of study participants for continuous collection of blood plasma every 30-60 minutes for melatonin measurements. 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. "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."

Other researchers working on the study include: 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.

Journal Reference:

Joshua Gooley et al. Exposure to room light prior to bedtime suppresses melatonin onset and shortens melatonin duration in humans. JCEM, March 2011

http://www.sciencedaily.com/release...10113082716.htm