We believed that sleeping with the light on could potentially harm one’s health, so we decided to conduct an investigation into the matter.
Circadian rhythms, which are tied to environmental signals, primarily light, regulate the sleep-wake cycle of both humans and many animal species. During the dark hours of the day, our internal clocks, specifically the suprachiasmatic nucleus, send signals to the brain that promote rest and recovery by triggering the production of melatonin, a hormone crucial for high-quality, healthy sleep. In contrast, throughout the day, these internal clocks generate signals that help us remain alert and active. Therefore, sleeping in a dark environment is essential for our bodies to rest and recover at night to stay alert during the day.
However, some people opt to sleep with the light on during the day due to a disrupted schedule or work pattern. This can be due to leaving the upper light or night light on or failing to turn off their phone or computer screens, which results in a lit bedroom. Additionally, the light from car headlights or street lamps may prevent complete darkness. Despite these reasons, the question remains: is sleeping with the light on really dangerous?
According to scientists from Harvard Medical School, room light – approximately 200 Lux – can reduce melatonin production time by 1.5 hours and decrease its quantity by 50%. This reduction in melatonin production could potentially affect the quality of sleep, as well as thermoregulation, blood pressure, and glucose levels in the body.
Northwestern University (USA) researchers conducted an experiment in 2022, in which 20 young individuals slept under different lighting conditions for several nights. One group spent a night with overhead lighting turned on and the next night almost without light, whereas the second group slept both nights in complete darkness. Although participants from the first group reported normal sleep, electroencephalography recordings of their brain activity during sleep revealed that they spent less time in the deep and rapid eye movement (REM) sleep stages, which are crucial for cognitive functions and considered the two most peaceful stages of sleep. Additionally, their insulin resistance, a crucial factor affecting the body’s ability to process sugar, was higher in the morning. Furthermore, their heart rate did not slow down throughout the night, which can lead to the development of cardiovascular diseases and premature death.
The same researchers conducted another study that confirmed the negative impact of light on the sleep of older individuals. This study monitored more than 550 participants aged 63 years and above for seven days, studying their sleep conditions and comparing the results with their medical indicators. The findings revealed that those who slept with light were more susceptible to cardiovascular diseases, obesity, and diabetes.
Over 1000 elderly individuals had the brightness of light measured in their bedrooms 2 hours before waking up by Japanese scientists. The findings revealed that those who slept with the lights on were more vulnerable to various sleep disturbances.
US National Institutes of Health scientists have suggested that sleeping with the light on may lead to weight gain and obesity. They arrived at this conclusion by studying surveys from over 43,000 women that included reports on their sleeping conditions. Findings revealed that those who preferred to sleep with the lights on or did not turn off the TV at night were more susceptible to obesity. However, the scientists caution that this factor is not the sole contributing factor to obesity.
The US National Toxicology Program experts added that working the night shift for an extended period and disrupting circadian rhythms can lead to the development and occurrence of cancerous diseases. The experts also point out that sleeping with light exposure can have similar consequences.
Smartphone, tablet, computer, and TV screens emit blue light, which stimulates the brain and suppresses melatonin, severely impacting sleep quality. Sleeping with the TV on, even without sound, or keeping a smartphone next to the bed with notifications that cause the screen to periodically light up is not recommended. These actions expose individuals to the most stimulating type of light, leading to a destructive effect on sleep quality.
To promote the production of melatonin and improve sleep quality, experts recommend avoiding the use of phones and laptops for at least two hours before bedtime and dimming the lighting in the room. Thick curtains or blinds can be hung in the bedroom to protect against external light sources, while sleep masks can be used as an alternative. However, it is important to note that uncomfortable sleep masks can have a negative impact on sleep quality. Spending more time in daylight during the day can also help reduce the negative effects of evening lighting on the body.
Specialists believe that sleeping with light exposure is indeed harmful to health. They assert that this type of sleep does not promote high quality rest and recovery. In the long term, it can also lead to the development of various health issues, including cardiovascular diseases, obesity, diabetes, and even cancer.
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