It’s often said that modern society appears to practically "manufacture" mental health problems. However, a new study hints that the modern “epidemic” of depression may be associated with a surprisingly simple and easily preventable factor: artificial light.
Japanese scientists have found that even the slightest slither of light when trying to sleep could be linked to a heightened risk of depression, according to a new study published in The American Journal of Epidemiology.
The reason behind this link is unclear, but the researchers believe it might be to do with the human circadian rhythm, the 24-hour cycle that tells us when to sleep and wake up, among other things, that is “programmed” by environmental factors. In the case of humans and many other creatures, light influences how much of the sleep-inducing hormone melatonin is pumped into our bodies, meaning we feel awake when the Sun rises and get sleepy when the Sun sets.
This system works like a charm when there’s only sunlight, moonlight, and a campfire to think about. However, the modern world is beaming with almost constant exposure to artificial light. Light at night (LAN) in a bedroom – even a flash of a digital clock or streetlight creeping in from a crack in the curtains – could screw with our natural sleep/wake cycle.
The team behind the recent study assessed the sleep of almost 900 elderly people with no signs of depression. They found that people who slept in a room with 5 lux of light or more at night showed a “significantly higher depression risk” than those who slept in a completely dark room. For perspective, a household room with its lights on is around 80 lux and 10 lux is a single candle from 0.3 meters (1 foot) away.
There are a few things to consider with this study. The majority of participants were fairly old, with an average age of 71, so it’s not exactly certain how well the findings represent younger people. Additionally, the research did not set out to find a cause-and-effect relationship, merely an association. As the study notes, “Although such low-level LAN may affect human circadian physiology, the association between exposure to LAN and depressive symptoms remains uncertain.”
There is also evidence from studies in humans that bright blue light in the evening decreases the quality of sleep compared to longer wavelength light, such as warm orange candlelight. This means that our smartphones and laptops, gadgets that many of us play around with just before bed, could be having a detrimental effect on our health.