Whether you’re working irregular hours, night shifts, doing a windowless desk job or outdoor physical labour – your occupation elects how you sleep.

When and where you work plays a vital part in how your body functions, keeping you in, (or firmly out of) equilibrium. “Evolution figured out a long time ago you can't sprint through life at a hundred percent speed and live for a long and fruitful time. You have to have a rhythm,” says Michael Grandner Professor of Sleep Behaviour at the University of Arizona. “Every cell in your body runs on timing mechanisms like millions of tiny gears in a watch that are in sync with each other, and these clocks are organized by peripheral clocks, which are all organized by a central clock in the brain.”

What he’s talking about here is circadian rhythms; your body’s innate time machine that all your organs adhere to. Disrupt these ancient rhythms and you disrupt the workings of every function in your body. In years gone by, we all rose with the sun, worked outside on the land and went to bed when it got dark; we were in tune with nature and so were our biological rhythms. Only now, most of the world’s population works indoors and when you change the external environment, you change your light–dark cycle, telling your biology that it’s wrong. The National Human Activity Pattern Survey reports that the average American spends 93% of their life indoors; 87% of their life is inside buildings and 6% of their life in automobiles. That leaves only 7% of their entire life spent outdoors. So is it any wonder we’re all firmly out of sync?

Timing is a huge factor for sleep, but equally so is light. “Human evolution occurred in equatorial places where the days are bright and the nights are dark and our bodies still expect these rhythms today,” explains Grandner. “On a relatively clear, bright day looking at the horizon, we get about 10,000 lux of light in our eyes. Then if we then walk inside to a bright office with bright overhead lights, you're talking about 500 lux compared to that daylight 10,000, but if you're working in a regular office, most are lit at around 300 lux. Now if you're in your house, you're down to around 200 lux and if you’re in the living room of that house with the curtains drawn, it might just about reach 50 lux. That’s 0.5% of the light your eyes should be receiving.”

What’s more, the frequency spectrum that our eyes are looking for in daylight is in the blue and green shades in particular, so the sky and the natural world frequencies of light go directly to our body clocks more than other frequencies. Therefore, if you have a job that gives you outside time your rhythms will be kept in beautiful equilibrium – another case of the great outdoors.

Research shows night shifts and rotating shifts shows are the most disruptive to our health, sometimes inducing what is now known as shift work sleep disorder. “When people work nights during the week but then try to keep daylight hours on the weekend, it’s as if the body is in a different time zone, multiple times around the week. It would be like living in London during the week, then going to LA on the weekend, then coming back for your Monday morning job in London. Your body becomes hugely stressed out by that and it takes its toll on everything from your immune system to your metabolism. That’s why shift workers get cancer more, suffer from heart disease more, and are more prone to diabetes,” explains Grandner.

This continuously moving target puts stress on the cells to function properly because they're forever out of sync with each other, trying to align.

Regular night shifts are a little different in that if you keep to the same shift all the time, you can train your biological night to be the solar day. Exposing the body to bright light at night can send that daytime signal to the brain, it's not easy to trick the body, and it’s certainly not without stress, but it is possible and still preferable to shifting around.

Heart racing, mind whirring, frustration building - there’s no one whose sleep isn’t compromised when they’re stressed. Medical studies show that work-related stress is amongst the biggest reasons for poor quality sleep. But this is not a shocking revelation to anyone with a hectic job role or demanding career.

But not all work stress inhibits sleep. If we leave enough time to allow our mental state to calm back down, being stressed during work hours should not negatively impact sleep. It’s when our occupational load spills over into our rest time, when hormones are kicked out of balance and cortisol and adrenaline run too high, too close to bedtime, that the body becomes vulnerable to bad sleep. “Highly stressful jobs with poor boundaries where you're carrying your work home into the evening, are not good for sleep,” warns Grandner. “The biggest problem with sleep and work is that we're never done. We do not give ourselves permission to be done, because there's always more.”

Bring the day’s work home with you, and that will impact sleep. We might not be able to change the nature of our working hours, but by switching off post-work, we can increase the quality of our sleep. The single most effective boundary to instil for better sleep is not checking emails for a 12-hr block between 7pm and 7am. “Remove emails from your phone so you’re not subjected to the flood of urgency and accountability. Set up an auto-responder to inform senders when you’ll respond, so that they don’t chase you,” advises Jayne Hardy of mental health charity The Blurt Foundation . Creating that boundary between work and rest gives the adrenals time to gently lower cortisol levels, changing the body into relaxation mode and a more restful, sleep-ready state.

New research by the University of California shows that crossing time zones can cause acute disruption of circadian rhythms, long after your flight home. But when so many of us are back to racking up the air miles for work and play, how best to protect ourselves through time travel?

Put in the ground work

The key to managing jetlag is to get yourself into the mindset of your destination early on. In the days leading up to your flight, adjust your bedtime by an hour a day. “Get more sunlight in the mornings if flying east and more in the evenings if flying west,” says Dr Tara Swart, Corinthia Hotel London’s Neuroscientist in Residence and author of The Source: Open Your Mind, Change Your Life. “Also, landing in the daylight will also help you adjust quicker.”

In-flight eating

“Fasting until breakfast time in the new time zone will help re-anchor the body’s rhythms,” advises Dr Swart. “Drink at least 500ml of still water for every 15kg of body weight. This will help to limit the particularly dehydrating effects of high altitude.” Then when it’s time to eat, stay away from the salted nuts which are highly dehydrating and choose any water-rich fruit like melon. Choose the fish option at meal time, fresh vegetables if offered and avoid pro-inflammatory starches and sugars that increase fatigue.

Bring in your own lighting

When you arrive at your destination, if you’re working your hotel room and feel yourself lagging, white/blue light has been proven to boost concentration and productivity levels. The Lumie Zest Lamp, £125, gives off the optimum daylight imitating brightness you need to stay alert and in the (time) zone.

Don’t take sleeping pills

Sedation might knock you out, but it can’t create restorative sleep. The LYMA Supplement contains the highest level of patented Sensoril® Ashwagandha, independently proven to send chemical sleep signals to the brain, whilst reducing cortisol and regulating blood sugar levels to put the body in a restful sleep state.