The dark side: How too much light is making us sick
We live in a world that loves the light, and shuns the shadows.
Associate Professor Sean Cain and Dr Andrew Phillips of The Turner Institute for Brain and Mental Health study the effects that artificial light has on our brains and physiology. Too much light is making us sick, they say, because it disrupts the body’s internal clocks – or circadian rhythms – that rely on a clearly defined cycle of night and day to function optimally.
“Yin and yang is all about the balance of light and darkness, and it’s important,” Cain says. “That's how we organise our physiology.”
Artificial light disrupts this rhythm, disturbing our sleep and affecting our health. “We’re confusing this system, and having more chronic illness as a result,” he says.
In their recent study published in Scientific Reports, Cain and Phillips evaluated the impact of modern home lighting environments, and how they affected sleep. The subjects in the study wore an individual light meter – called a spectrophotometer – that was developed with engineer Vineetha Kalavally, a co-author on the study, from the Monash University Malaysia campus.
The new wearable is a small clip-on device that can be worn on the upper body. It measures all wavelengths of light.
Crucially, it accurately measures how our body’s circadian clock perceives light. This allows the device to measure the negative impacts of evening light exposure on our circadian clock and sleep, including reduced production of the sleep-promoting hormone melatonin.
“We think eventually the device will be used in the treatment of depression, and sleep disorders, and basically feeding back to people this non-conscious information about what kind of light they’re in,” Phillips says.
“It’s almost like a third eye, so it tells you something that you’re not consciously aware of, because this photoreceptor system, it’s very ancient; it feeds into old, subcortical areas of the brain,” Cain says.
Nearly half of the homes in the study had bright enough light to suppress melatonin by 50%. But the study also found that the effect of artificial light on individuals varied greatly – by as much as 50-fold – and was difficult to predict.
Phillips and Cain were just awarded an ARC Discovery Project grant to investigate how these individual differences in sensitivity to light affect shift workers.
“We now live in this kind of twilight zone,” Cain says. “When we evolved, it was very bright in the day, with quick transitions between darkness and light. But now we live indoors, so we’re not out in bright daylight so much. And at night, we’re not in darkness anymore. We’re living in that in-between region, between darkness and light now. And that’s where you see the big inter-individual differences.”
On nights when individuals had greater exposure to light in the evening, they were also found to have more trouble getting to sleep, the study found.
Critically, homes with energy-efficient LED lights, the type distributed by the Australian government to reduce household carbon emissions, had nearly double the melanopic illuminance of homes with old-fashioned incandescent light bulbs. This is because incandescent bulbs emit light on the red-end of the spectrum, whereas most LED light is blue – like the light on mobile phone and computer screens.
The adverse effects of blue light
Blue light is particularly disruptive to our circadian rhythms.
“So while we’ve been doing the right thing for the environment by changing to energy-efficient lights, we’ve likely been having a negative impact on our sleep, mood and general heath. In time, we may find that those negative effects were much more costly than the energy savings.” Phillips says.
It’s possible to modify the artificial light so it’s less disruptive, he says, by choosing LED lights that are yellow and warm, rather than blue and cool, for instance. Or installing dimmer switches to decrease the light in the house before bedtime. Watching movies on a TV screen on a dim setting, rather than a bright computer on your lap, can also lessen the impact of their blue light.
“If you look at all of human evolutionary history as a 24-hour day, we've had control of our lights for the last 77 seconds of that day,” Cain says. “We did not evolve to control the light, and our bodies don’t expect light at the wrong times. And when they get it, the whole system of these clocks in our bodies gets messed-up, and we’re all a little bit more tired, a little bit more miserable.”
"While we’ve been doing the right thing for the environment by changing to energy-efficient lights, we’ve likely been having a negative impact on our sleep, mood and general heath."
“Once you disrupt these rhythms, you can have countless chronic, negative health effects,” he says.
“Your weaknesses will start to be exposed. So if you’re someone who is more likely to develop cardiovascular disease, that might show up. If you're more likely to have diabetes or metabolic disease, they will show up. In animal models, and even in humans, you can create essentially almost any chronic disease by disrupting sleep and circadian rhythms.”
Even daylight saving disrupts the natural rhythm, and can have health consequences.
“It artificially moves us away from the natural light-dark cycle,” Phillips says. “There are some interesting studies on people who live on the eastern versus the western side of time zones, which is similar to living in standard versus daylight saving time. People on the western edge of time zones have more health problems.”
Light is a mood-enhancer
But daylight saving is popular, because people enjoy the extra exposure to light.
“Light makes us feel like we're in a better mood, and it’s probably why at night a lot of people do seek light and look at their phones,” Cain says. “It’s probably why people over-light their outdoor environments and create light pollution...it makes us feel safe and a little bit happier.”
Cain has a paper now under review that examines the physiological reasons for this, describing the parts of our brain that are affected by our exposure to light. His previous research has looked at how antidepressants (selective serotonin re-uptake inhibitors) increase people’s sensitivity to light, which may be what makes them feel better.
“Whether they work or not will depend on the balance of your daytime light and your night-time light. So if you get too much night-time light, it could undo the good of enhancing the daytime light.
“And it's interesting that people who get more light at night are evening-type people. About half of people who are depressed are evening-type people, and those people benefit less from antidepressants. But if you look in the general population, it's only about 20 to 25 per cent.”
Cain and Phillips have an active NHMRC Ideas grant to investigate how light sensitivity is a core mechanism for antidepressant efficacy.
Cain is also examining how language reflects how our bodies and minds respond to light and dark.
“For example, looking on the bright side of things. Darkness is associated with chaos. Without light, there’s more chaotic thought, and a lot of people have problems sleeping, problems with anxiety, because in darkness they're less able to control their emotions.”
We fear the dark for a reason, but we also need the dark to restore balance to our bodies and minds.