Researchers link sleep problems to viewing blue-light screens before bed
Exposure to blue light from screens such as laptops, tablets and smartphones harms our sleep, according to a study conducted by researchers at the University of Haifa and at the Assuta Medical Center Sleep Medicine Institute in Tel Aviv.
While exposure to screens that shed blue light before bedtime impaired quality of sleep, screens that emit normal, or closer to full-spectrum, light yielded results similar to those in people who had not been exposed to any light.
“Fortunately, there are various applications that filter out the problematic blue spectrum and create a weak red filter that reduces the effect of suppression of melatonin,” said University of Haifa biology Prof. Avraham Haim, one of the lead researchers.
“The light that emanates from most screens is blue light that affects our body cycles and sleep,” he noted in the study just published in the journal Chronobiology International. “The solution should be the use of filters that exist today that prevent that emission.”
Previous studies have found that watching such screens before sleep affects sleep. Other studies have found that exposure to blue light at short wavelengths, between 450 to 500 nanometers, reduces the production of melatonin, a serotonin-derived hormone secreted by the pineal gland in the brain at night and linked to a normal biological clock and routine sleep rhythms.
The current study was conducted by Haim and doctoral student Amit Shai Green of the Israel Center for Interdisciplinary Center for Research in Chronobiology at the University of Haifa and the Institute for the Study of Sleep and Fatigue at Assuta, Dr. Meirav Cohen-Zion of the Tel Aviv Academic College of Behavioral Sciences and Prof. Yaron Dagan of the Institute of Applied Chronobiology at Tel Hai Academic College.
The researchers examined whether there is a difference in sleep characteristics when subjects were exposed to blue or red light before going to sleep.
The study involved 19 subjects aged 20 to 29 who were unaware of the purpose of the study. In the first part, for one week the subjects wore an electrocardiograph that objectively examined their sleeping and waking time. They also filled out a sleep diary and a sleep-quality questionnaire.
In the second part, which took place in Assuta’s sleep lab, participants were exposed to screens between 9 and 11 p.m., when the pineal gland normally begins to produce and secrete melatonin.
After exposure to the light, the study participants were connected to devices that read brainwaves and determine the various stages of sleep a person undergoes during the night, including unconscious awakenings. In the morning, participants filled out questionnaires about how they felt.
The results showed that while exposure to red light showed a very similar picture to “normal” sleep – that is, without exposure to light before bedtime – exposure to blue light impaired the quality of sleep. It was also found that exposure to strong blue light generally affected the quality of sleep, but the effect was much smaller than that of low-intensity light, either blue or red. That is, the wavelength determines the quality of sleep.
On average, exposure to blue light caused shortening of sleep time by about 16 minutes. It also caused a significant halt in the production of melatonin, while exposure to red light showed melatonin production similar to normal. According to the researchers, harmed melatonin production indicates a significant disruption of the natural mechanisms and the body’s biological clock.
In addition, it was found that exposure to blue light caused the body not to perform the natural mechanism of lowering body temperature.
“Naturally, when you fall asleep, the body begins to lower its temperature until it reaches the lowest point around 4 a.m.,” Haim said. “Then, when the body returns to the normal temperature we wake up. After exposure to red light, the body continued to behave naturally, but exposure to blue light caused the body to maintain a constant temperature until awakening – further evidence of damage to our natural biological clock.”
The biological findings showed evidence that continuity of sleep after exposure to blue light was most drastically affected, while after exposure to both intensities, people woke up on average 4.5 times in unexplained arousals. Exposure to bright blue light caused awakening at night of an average of 6.7 times. It was thus not surprising that in the morning questionnaires, the subjects reported that after exposure to blue light, they felt more tired and in a worse mood.
“Exposure to screens during the day in general – and at night in particular – is an integral part of our technologically advanced world and will become more intense in the future. However, our study shows that it is not the screens themselves that damage our biological clock, and therefore our sleep, but the short-wave blue light that they emit.