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Light is like a drug’: How to reset your circadian rhythm

circadian rhythm

Our body clocks control the rhythms within our body and setting them each day can make a difference to our health on every level.

If there was ever a reminder that we are human, in an increasingly mechanised world, it might just be our circadian rhythm. And this is because the thousands of invisible clocks that live within our bodies sync their time each day and pulse to the rhythm of nature.

These clocks then harmonise all of our daily rhythms from sleep and wakefulness, hunger, digestion, mental alertness, and mood, stress, heart function and immunity. As our bodies rise with the sun, hunger, digestion, cortisol levels, heart rate, mental sharpness and mood lift too. As the sun lowers, our bodies also wind down. The “darkness” hormone, melatonin, kicks in, our digestion slows preparing for rest, our hearts shift into repair mode, stress hormones taper off, our mental sharpness and activity softens and our body temperature starts to drop. This is all in theory, assuming our clocks – and bodies – are operating according to their design manual.

“One of the issues is we’re working against our rhythms – the natural rhythms of life have been disrupted by socially constructed rhythms,” says the Sleep Health Foundation’s Moira Junge.

In the world we live in it is easy to throw off the delicate dance between our body clock and nature’s cues. And this is largely because humans were made to dance in time with nature, yet few of us in the modern world do.

“Our bodies expect and evolved to have very bright days and very dark nights and when we have that strong signals for light and dark, our bodies are synchronised in the way they evolved,” explains Sean Cain, a circadian biologist and Associate Professor of Psychology at Monash University.

When we are in harmony, we are healthy. When we don’t harmonise, however, it causes an internal cacophony disrupting our sleep, health, weight and mood.

Daylight savings demonstrates the impact this can have.

When we lose just one hour of sleep, research has found heart attack rates increase as much as 24 per cent and when we gain an hour of sleep, there is a 21 per cent reduction in heart attack rates.

Scary as this sounds, it’s about our alignment with light and dark outside not just whether we had seven hours versus eight hours sleep.

Cain explains: “Your body doesn’t care what you call the time. It lines itself up with the sun. When time changes we suddenly change all our behaviour, but our clocks don’t really change or adjust, so you end up living slightly out of time with your body. That results in an increased vulnerability to chronic illness.”

“We have not had time to adapt to having total control of our lighting … it’s like the Wild West out there in people’s homes.”

Sean Cain, Monash University

And when we consider this profound impact of slight misalignment with our environment we can see how modern life cycles of not very bright light in the day and over-lit homes at night can throw us out even more.

“It causes these clocks within the body to be confused and out of sync with each other and out of sync with the world which makes us more vulnerable to sleep, mood and general health problems like metabolic disorder and things like that,” Cain explains. “We really need to change the way we think about light and dark.”

Surely, it’s not that big a deal, I argue. We were using fire at night long before the light bulb was invented in 1879.

Bright lights that can be switched on any time of day or night are a relatively new invention, Cain responds: “We have not had time to adapt to having total control of our lighting and spending something like 80 per cent of our waking days indoors. It’s like the Wild West out there in people’s homes.”

Ron Grunstein, the head of the Sleep and Circadian Research Group at the Woolcock Institute of Medical Research, agrees:

“I think the biggest problem is what we do to ourselves in our homes… the intensity of the light, and staring into the computer screen late at night.”

Interestingly, we are like moths to a flame when it comes to bright light, even when it’s doing us and our circadian rhythm harm.

“Light suppresses activity in the amygdala, which is an area in the brain that is involved in fear, and negative emotionality,” Cain explains. “In other words, it makes us feel safe. It also leads to increased connectivity between the prefrontal cortex and the amygdala. The prefrontal cortex is involved in our ability to control our emotions, so at night, no wonder we’re drawn to light – it makes us feel better, it makes us more in control of our thoughts and feelings and because it’s as easy as switching on a light or looking at our phone, of course we consume it.”

For our health, and our sleep, however, we need to learn to consume it at appropriate times.

Though we may not be able to change the rhythms of modern life, there are easy ways to reset our circadian rhythm each day to enhance our health and align better with nature’s cues.

See the light

Perhaps the single most important thing we can do is expose ourselves to bright light as soon as we wake up. Open the curtains, turn on the lights and go outside. At work, sit near a window to get natural light, or if you can’t do that, ensure the lights are bright and aim to get outside for breaks.

The central clock at the base of our brain, called the suprachiasmatic nucleus, acts as the conductor to all the other clocks in our body. It directly connects with our eyes, and by perceiving light, that clock knows what time of day it is.

“Light is like a drug.”

Sean Cain

For this reason, Cain says: “From dawn to dusk if the sun is up, you should be getting as much light as you can… the more bright light we get, the healthier we are.”

Try it for a week, he suggests. “Stay in an annoyingly dim light at night and, if it’s daylight, get out in the light and work out, outside, if you can.”

Not only does bright light in the morning set our internal time correctly, but a study of 400,000 people found the amount of outdoor light they got was related to increased happiness, less likelihood of ever being diagnosed with depression, less antidepressant use, and better sleep. Why better sleep?

“We have sleep pressure that builds from the moment we are out and exposed to light …. We want it to be as high as possible to get a good chunk of sleep in one consolidated chunk,” Junge explains. “Getting exposure to morning light can change things.”

Time your eating

While light is the primary time-keeper of our body clock, food also sends signals to our body, via our food-entrainable oscillator, about the time of day. This means that when we eat late at night, when our body clock is in rest and repair mode, our circadian rhythm is confused and there can be detrimental knock-on effects.

“Eating tells the body that it’s daytime, it’s eating time, and it’s getting your digestive system ready to work when what it wants to do is repair, relax and get into sleeping mode, not working mode,” explains Cain.

Time-restricted eating (TRE), where we eat all our food within a window typically between eight and 12 hours, is a way to stabilise the signals of the clocks in other tissues of our body.

“I’m very diligent about the timing – you want to be eating at a time your body expects to eat and the more regular you are with giving those signals to your body, the better it operates,” says Cain, who eats in an eight-hour window. “What your body doesn’t expect is to eat at night. If your melatonin is rising you should not be eating.”

Grunstein has done studies giving people Mcdonald’s burgers at different times of day. “Your triglyceride levels are higher if you eat a burger at 9 or 10 o’clock at night than if you do at lunch,” he says. “Timed eating is reasonable and there’s growing evidence it is effective.”

And though a Maccas burger at lunch is better than late at night, what we eat is as significant as when we eat, as demonstrated by emerging research into the impact the quality of our gut bacteria has on the quality of our sleep.

Switch off your body clock

As it starts to get dark outside our brain gets the message to secrete the hormone melatonin. At least that’s what is meant to happen.

“We’re now living in a perpetual twilight in the evening. We suppress melatonin signals with our indoor light and phones,” Cain says. “We’re in the dark in the day and in the light at night. It’s no wonder the system is messed up.”

Junge adds that people feel like they’re getting around it with the blue light filters: “Blue light is known to suppress melatonin, but it’s not just the blue light it’s the stimulation still as well at the time the brain is doing it’s best to get sleepy and unwind.”

So, the light from the TV may not be a huge issue in and of itself, but watching it late at night eats into sleep time and stimulates our brains when they’re trying to switch off. Switching off our brains also requires attention to the lights in our home at night.

“Light is like a drug. You look into a light at night, and it goes straight into the clock and tells the clock it’s not night its day, and it will start doing day things,” Cain explains. “It’s really hard to get to sleep when your clock is telling you it’s day time.

“If the sun is down, avoid light, dim the lights or go for light that is more orange, red or yellow.”

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