How blue light treatment in surgery speeds recovery

We’ve long looked to the birds and the bees to unravel nature’s mysterious cycles.

Much behaviour in the animal kingdom is centred on the circadian rhythm – whether it’s birds heading elsewhere for winter, or bees finding their way to flowers at exactly the right time.

Dr Guy Warman is an associate professor in the School of Medicine who specialises in anaesthesiology and chronobiology (circadian rhythms). In recent groundbreaking research with Dr James Cheeseman from the Department of Anaesthesiology, bees helped the team see the light, so to speak.

The research arose from wondering if there was a way to prevent the ‘jet lag’ patients suffer when they are anaesthetised during an operation.

“Drugs – particularly anaesthetic drugs – affect the biological clock and affect sleep,” says Dr Warman. “But it was hard to get robust findings because most patients admitted to hospital are already sick, so their sleep is already disrupted. We took a step back and thought ‘let’s follow up on some research we’ve done with our chronobiology interests’. That’s what took us to bees.”

A common patient response when they wake up from anaesthesia is that they think no time has passed.

“Some even say, ‘well when are you going to start my operation?’ We thought that was interesting and probably due to a biological clock effect. The reason to study bees is that they show time-compensated behaviours.

“They do this thing called a ‘waggle dance’ in the hive that tells the other bees where a food source is. By tracking their behaviours, you can work out exactly, to within a few minutes, what time of the day the bees really think it is.”

For example, when bees head off from the hive each day, they always fly in a certain direction. The team wanted to see what would happen if they anaesthetised a bee and then woke it up.  

So how do you anaesthetise a bee?

“We used a common anaesthetic agent to knock out the bees for anything from a few minutes to six hours. Then we looked at which way they flew when they woke up from anaesthesia.

“We collaborated with scientists in Germany and used harmonic radars – we put radar tags on the backs of the bees, like an antenna. By using those antenna and a very powerful radar, you can track where the bees fly.”

The bees that hadn’t been anaesthetised for long just compensated for the movement of sun in the sky.

“But the bees that had been anaesthetised for six hours flew the wrong way because they thought it was the same time as when they went to sleep. They still thought it was 9 o’clock in the morning. They had jet lag.”

As well as doing the experiment during the day, they did it at night and there was no jet lag.

“That got us a little bit excited. We started looking at the combined effect of light and anaesthesia and found that in the morning, when anaesthesia caused a delay to the biological clock – jetlag – the light caused an advance to the honeybee clock.”

The next test was to give anaesthesia with strong light. “The jet lag went away. And then we thought we might be onto something, so we transferred the study from bees to humans and other mammals, as well as fruit flies.”

The problem was finding enough healthy humans, who previously had no sleep problems, who might be undergoing an operation. 

“We hit upon the idea of doing studies in kidney donors,” says Dr Warman. “They are healthy people, but undergoing a major surgical procedure that they don’t medically require, and they’re screened for sleep and mood disorders beforehand.

“They’re also extremely kind, altruistic people who are more than willing to help out.”

The team did the same thing with the kidney donors as they’d done with bees, measuring their circadian rhythms before and after surgery.

“Then we gave half of the participants blue light while they were anaesthetised, because it’s known to shift the human circadian clock.

“And we gave half of them red light, which we call placebo light, which is known not to shift humans’ circadian clock.”

The 40 patients in the trials wore goggles that emitted blue light flashes through their eyelids every 30 seconds.

“Excitingly for us, the patients in the blue light treatment group showed less jet lag than those in the control treatment group.”

The less jet-lagged a patient is after an operation, the quicker they are up and about and the sooner they are discharged from hospital. But that’s not all.

“There are more fundamental effects,” says Dr Warman. “It’s entirely plausible that by preventing circadian misalignment or circadian disruption that wound healing and immune function might be less disrupted as well.”

Now Dr Warman and his team are on the verge of expanding their research – pending funding – to a multi-centre international trial with a larger patient group.

It seems ironic that blue light – the target of much bad press – could have such unexpected health benefits.

“The blue light we use is 460 nanometres – a very specific wavelength that the circadian system is attuned to,” explains Dr Warman.

“The way your biological clock is adjusted by light daily, is through a set of receptors called intrinsically photoreceptive retinal ganglion cells. They have a pigment in them called melanopsin which is maximally sensitive to 460 nanometres, which is blue light.

“Despite the fact sunrise and sunset look pinkish, actually the most light that’s getting to your eyes is blue. Your eyes attune to that light to keep your biological clock adjusted.”

Which is good when it happens in the morning, but it causes problems at night through devices, TVs and even lights in our homes, which are all far bluer than we’ve previously experienced. 

“When I grew up, it was all tungsten bulbs and there was much less blue light,” says Dr Warman. “Although you can buy LED lights in any spectrum – dark red or yellow or whatever – the ones installed in houses and buildings tend to be of a bluer wavelength than we’ve previously been exposed to. So this is the concern.”

The Blue Light Aotearoa document produced by the Royal Society of New Zealand states blue-light exposure is an important issue for society.

“Exposure towards bluer-enriched light, including LED lighting in the street at night-time, delays your circadian clock,” says Dr Warman.

“Blue light in the morning shifts your clock to an earlier time zone. Blue light in the evening delays your clock to a later time zone.

“Architects are well aware that light is important. Morning light is particularly important and certainly there is a move in building design to try and maximise that.”

He says blue light in the morning has been used for decades to improve sleep and to reduce depression.

“There are cafes all through northern Europe where you can sit down in front of a lightbox in winter to try and avoid seasonal affective disorder, because that disorder is simply a biological clock misalignment.”

And while there are lots of reasons for sleep disorders, late-night blue light seems to be one. “Exposing ourselves to the light at the wrong time of the day – by sitting on devices late into the night – compromises our sleep duration and quality. You shift your clock to a later time zone.”

Which is fine if you’re undergoing surgery it seems, but not if you want a decent sleep.

By Denise Montgomery