Why sleeping in a dark room is better for your health

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Even if you’re afraid of the dark, it might be time to turn off the lights and invest in blockout curtains, according to new research.

A study published in the American Journal of Epidemiology has found that exposure to light at night while sleeping, even at very low levels, is linked to an increased risk of depression.

Nighttime light has been shown in the past to disrupt sleep-and-wake cycles, affecting the quality of sleep. It’s an ever-growing concern with more people regularly using their phones in bed or leaving the TV on as they sleep.

This new study goes further, identifying how even low levels of nighttime light can negatively impact mood and mental wellbeing.

Researchers in Japan measured exposure to nighttime light levels in the bedrooms of 863 elderly people over two years by placing ceiling-facing light devices at the head of each participant’s bed for two nights.

The study took into account weight, smoking and/or drinking habits, medication use and income level. Other factors included histories of high blood pressure, physical activity levels and diabetes. The subjects also had to complete sleep diaries and were monitored through long-term surveys for the development of depressive symptoms.

The researchers found that those exposed to more than five “lux” of light each night had higher rates of depression. The standard one “lux” measure is the amount of light emitted by a candle if you’re located one meter away. The study noted that five lux is roughly equivalent to a street light shining through the window into a darkened bedroom.

Around 150 people slept in rooms with more than five lux of light, with this group showing a 65% increased chance of developing depression after two years compared to those who slept in completely dark rooms. Those with light at night also had a tendency to go to sleep earlier, wake up later and spend more time in bed overall.

Previous research has suggested the possibility that LAN (light-at-night) induces sleep disturbances, impaired melatonin secretion and misalignments between sleep-and-wake behaviour, with depression frequently being accompanied by these conditions.

The study’s co-author, Professor Kenji Obayashi from the Nara Medical University School of Medicine, said the results suggest that sleeping in total darkness might be good not just for your quality of sleep, but also for your mental health.

“Maintaining darkness in the bedroom at night may be a novel and viable option to prevent depression,” Professor Obayashi told TIME magazine.

While it’s not entirely clear how LAN is linked to depression, Professor Obayashi suggested that it causes sleep disturbances that can lead to depressive symptoms, with teenagers at the greatest risk due to the use of devices before bed.

Clinical psychologist and head of paediatric sleep research at Central Queensland University, Professor Sarah Blunden, said that light exposure has been commonly used as a tool to improve people’s mood. For example, it has been used to treat people with depressive symptoms or suffering seasonal affective disorder, she noted.

“This (new study) flies in the face somewhat of what we have seen about light being good for depression,” Professor Blunden said.

However, it’s absolutely possible that there’s a correlation between LAN and depression, she added.

“My take on this is that if you expose people to light at bedtime, you may suppress the sleep-promoting hormone, melatonin, which is closely linked and even interrelated,” she said.

Improving sleep with the basics

As a way to improve the quality of sleep, well-designed pillows and mattresses are integral elements to consider investing in. Recent Canstar Blue research found that 34% of Aussie consumers purchased their pillow to help with a specific sleeping condition. Furthermore, 29% wished they had spent more on a better pillow.

For new mattresses it was found that more than half (55%) of survey respondents wished they had tried out their mattress before purchasing it.

With the average person spending around one-third of their life sleeping, it’s important to find as many ways as possible to maintain the quality of sleep.

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