Dr Cain said the lockdown has exacerbated this situation, but not all experts agree.
The circadian master clock, located in the hypothalamus, influences an extraordinary array of bodily processes, including sleep, obviously, but also hormones, digestion, and body temperature.
The clock is set by exposure to light. Human eyes have certain cells dedicated to the task of sensing light levels and signalling our circadian system.
Dr Cain argued modern lives exposed people to enormous amounts of artificial light which can mess with the body clock. If the clock is out of sync with people’s lives, they can end up living in a perpetual jet lag, he said.
“If your clock is not getting those regular signals – and it needs to be reset every day,” he said, mood and sleep “kind of fall apart.”
Australia’s lockdown has resulted in many people being confined to their homes for months at a time. That has presented Dr Cain with a giant human experiment to test his theory.
Before lockdown began, he had been running an experiment involving people wearing small light-monitoring pins on their clothing.
The research has yet to be published but Dr Cain said he found people were dramatically over-lighting their homes.
“The average home was bright enough to suppress about 50 per cent of our melatonin, all the way up until sleep. So that signal promoting sleep in the average home, it’s halved.”
It’s likely that being stuck at home during lockdown has made those effects worse, said co-director of the Behaviour-Brain-Body Research Centre at the University of South Australia, Professor Siobhan Banks.
“It’s potentially one of the factors that could lead to moodiness and anxiety and depression.
“Obviously there’s a lot going on, and there is going to be a lot of factors that affect how people feel. But definitely the disruption to sleep and our normal circadian rhythms would certainly be playing a part.”
University of Sydney circadian rhythm researcher Dr Yu Sun Bin said the basic science was sound, but questioned whether the lockdown really was causing us to spend more time inside.
“The reason I’m sceptical with that is normal life, we spend so much time in doors, that for a lot of us COVID has not changed that. I’m sitting at home, in artificial lighting, in front of a computer – and that’s what I’d be doing normally anyway.”
One thing the researchers agreed on is that if individuals are feeling sluggish, moody and tired, they should consider getting some early-morning sun, perhaps by walking outside without sunglasses.
Natural sunlight is brighter than artificial light and comes in a spectrum that has more of an effect on your body clock.
And sunlight at the start of the day is essential to setting the clock, Dr Cain said.
The professor himself takes things a step further, turning on all the lights in the morning and turning them down after dusk, leaving him “living in gloom”.
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Liam is The Age and Sydney Morning Herald’s science reporter