blue light

Blue light at night can disrupt your body clock, but it’s not all bad

For the past decade, scientists have been exploring whether artificial light — particularly wavelengths of blue light — poses a risk to human health.

You may have heard that too much screen time in the evening is a bad for you, and it’s true the blue light emitted by devices like phones and tablets can disturb your sleep.

But blue light is not all bad — and here’s why.

Blind mice sense blue light

In 2002, scientists identified a new type of photoreceptor cell in the eye, when the visually blind mice they were studying were still able to respond to certain wavelengths of light.

The cells, called Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) respond to light for regulating our circadian clock — not for forming images like the rods and cones in our eyes do.

By detecting how much light is in our environment, the cells can communicate to our brain and body that it’s day-time, or that it’s time to sleep, thereby setting our circadian clock, according to neuroscientist Stuart Peirson from the University of Oxford.

IpRGCs are most sensitive to light wavelengths of 480 nanometres — right in the blue light spectrum.

But Dr Peirson said in actual fact, IpRGCs can detect most wavelengths of light, and it can all disrupt our circadian clock.

Disrupting your circadian clock

In modern society, artificial light is all-pervasive — and it’s messing with our bodies’ expected light-dark cycle, according to psychologist Lora Wu from Massey University, who contributed to a report on blue light released this week by Royal Society Te Apārangi in New Zealand.

What is blue light?

  • Blue light is the higher energy, shorter wavelengths on the visible light spectrum.
  • Natural blue light is highest in the middle of the day, and is also emitted from devices like smartphones and computers.
  • Daylight is a combination of the whole spectrum of visible wavelengths of light.
  • Photoreceptor cells (ipRCGs) in the human eye respond to blue light to set our circadian clock.
  • Blue light is also emitted by ‘white-coloured’ LED lights.

“We’ve got a master clock in our brain, which is set by light exposure to the eye. And every organ and cell in your body has an internal clock as well,” Dr Wu said.

These conflicting signals between your body clocks can lead changes in your physiology and behaviour — for example your mood and metabolism.

Shift workers — who often need to sleep and eat at odd times — are prime candidates for circadian desynchrony.

And Dr Wu said in general, humans find it very hard to adapt to such disruptions, with one exception.

“Sometimes people think if you’re a permanent shift worker, you can essentially flip your clock and then be awake and working at night and asleep during the day. But the only place where that’s been demonstrated is in offshore oil rigs,” she said

On offshore rigs, it’s possible to have complete control over the physical and social environment of the workers, so their meals, light exposure and socialisation are all shifted to night time.

“In the case of [offshore rigs] you may see some adaptation in day to day life,” Dr Wu said.

When it comes to blue light, it’s the timing of your exposure that matters for your health.

And you can get this naturally from daylight.

But there’s solid evidence to suggest that if you’re getting too much blue light before bed from devices like phones or tablets, or from cool-coloured bright lights, it’s going to interfere with your body clock.

And that’s because the ipRGCs in your eye — which are highly sensitive to blue light — are telling your brain it’s not time to sleep yet.

Blue light and mental illness

Regulated exposure to artificial light has been used to treat seasonal affective disorder (SAD) for a long time, and Dr Wu said blue light therapy is now a standard treatment for major depressive disorder too.

“Adding artificial light to standard treatments for depression has been shown to be really effective,” she said.

People with mental health issues are more likely to have a disrupted daily rhythm, said Dr Wu, including sleeping during the day or staying up late at night.

“We see a loss of rhythmicity in conditions like bipolar disorder and also with suicide outcomes — basically any kind of behavioural or mental illness,” she said.

Because the circadian rhythms of people with depression are dampened, getting exposure to blue light in the morning — as well as restricting it at night — can help to reset the body’s natural rhythm, potentially improving sleep and mood.

And getting an early night can help too.

Australian research published earlier this year suggested that SSRI antidepressants were less effective for night owls, compared to early risers.

SSRI’s, or selective serotonin reuptake inhibitors, work by boosting how your circadian clock responds to light, which is meant to be stabilising if you wake and sleep at normal times.

But because night owls are exposed to more light in the evening — often blue light from screens — the SSRI’s can put their body clock out of whack even further, and stop the treatment working for the underlying mental health condition.

And poor sleep quality and lack of routine can contribute to poor physical and mental health, setting an unhealthy cycle in motion.

In recognition of the links between sleep quality and good health, an inquiry into sleep health awarenessin Australia was launched in September 2018.

UV light the real issue in eye disease

When exploring how blue light affects human health, the conversation inevitably turns to whether blue light is harmful to your eyes.

According to the Royal Society Te Apārangi report, while high intensity light exposure can cause serious damage to the retina, the blue light emitted from phone and computer screens is well below that harmful intensity.

The report also suggests that there is no evidence of a link between blue light exposure and eye disease including macular degeneration.

In 2017 it was reported that vitamin companies were selling products claiming to protect kids’ eyes from the blue light emitted from their electronic devices — claims that were dismissed as ‘ludicrous’ by eye doctors.

People, particularly parents, should be more worried about UV light, according to ophthalmologist Shanel Sharma, a member of the Royal Australian and New Zealand College of Ophthalmologists’ Public Health Committee.

“Blue light is getting a lot of attention, but it’s not related to eye disease,” Dr Sharma said.

Dr Sharma is a practicing paediatric ophthalmologist in Sydney and regularly treats children with eye damage from UV light.

She said while parents often think about protecting their kids’ skin, eye protection is not prioritised highly enough.

Dim the lights at night, or go camping

There are some relatively easy changes people can make to their behaviour to minimise the risks of body clock disruptions from blue light at night, psychologist Dr Wu said.

“Try to get daylight in the morning, limit blue light from devices at night, and replace cool/white-coloured lightbulbs with warmer-coloured ones,” she said.

One study found that going camping for the weekend and avoiding all artificial light sources could reset your circadian clock.

Camping isn’t the whole solution, of course.

But the research reinforces the importance of the natural light-dark cycle in regulating our body block.


Article appeared on ABC Health & Wellbeing

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