For the thousands of years that humans have existed on this planet, our circadian rhythms have been perfectly synchronized with the day:night cycle. We stayed awake during the day, working in the fields, exploring new territories, and hunting. At night we rested, with only a few individuals staying awake to protect the community from attacks by large animals and other dangers. As communities developed further, soldiers began to mount surprise attacks at night to gain an advantage over opponents. Explorers learned to navigate at night by following the position of the stars and moon. As the industrial era began, it became economically cost-effective to keep the engines of the economy running around the clock. This created a new group of workers – shift workers – who came to work in shifts to continuously man the production machinery, thereby producing goods more quickly and improving the economy of the region.
Going to work in shifts or working a few late-night hours every day was the key to building a better economy and society at large. Slowly it also became apparent that for an individual to be wealthier than others, it was important to work a few extra hours each night. However, this lifestyle of staying awake for longer periods of time – which began a few hundred years ago, particularly among shift workers – is known to disrupt circadian rhythms in physiology, metabolism, and brain function, and to increase the chance of developing many chronic diseases, even cancer. This growing connection between shift work and chronic diseases is ignored by most of us, as we typically don’t think of ourselves as shift workers (e.g., a factory worker, active duty military personnel, or first responder). But, there is a hidden epidemic of shift work-like lifestyles that have been overlooking for years.
Let’s define shift work, as well as the forms of shift work that can disrupt our circadian rhythms in ways that increase our risk of developing a chronic disease. The term shift work is defined differently in different countries and by different agencies. Some say that any work done outside 9 am to 5 pm (i.e., regular working hours) is shift work. According to the International Labor Organization, shift work is defined as staying awake 3 or more hours between 10 pm and 5 am for at least 50 days in a year. Why only 50 days in a year? Because once we disrupt our sleep for 3 or more hours and work under artificial light, circadian rhythms of different hormones, brain chemicals, and metabolites are disrupted, and even if we go back to doing regular shift work, our internal clocks will stay de-synchronized for up to a week. So, staying up late one or two days each week can offset circadian rhythms enough that our circadian clocks are playing catch up all the time.
This means that there are many ways we can disrupt our circadian rhythms; we don’t have to be working the night shift. Many of us don’t realize that if we stay up late a couple days a week, then we are living the life of a shift worker and that this lifestyle will cause long-lasting harm to our brain and body. There are at least 5 lifestyles that terribly disrupt circadian rhythms.
Shiftwork – Nearly 20% of the workforce in industrial countries are card-carrying shift workers. They include people working in the military, airline industry, transportation, food services, police, first responders, etc. They continuously work in these roles for years. In some professions (e.g., military, police, and firefighters) there is enough physical activity to counteract some of the adverse effects of shift work. Nevertheless, they cannot overcome the psychological stress of not sleeping enough or working in shifts. In the airline industry, safety and security concerns have led to better implementation of rest time between shifts, allowing employees to recover from circadian disruption, but some individuals may need more recovery time than others. The good news is that growing awareness about the adverse health impacts of shiftwork is leading to improvements in work schedule, downtime, extra compensation, etc. in many sectors of shiftwork.
Second-hand shift workers are the spouses or loved ones of shift workers who may also stay awake late into the night, or whose sleep and eating schedules are disrupted because they want to interact with their shift-working loved one. We became aware of the prevalence of this group while studying human eating and sleeping behavior for several weeks. In this study, we implemented strict criteria for excluding traditional shift workers. But when we analyzed the sleep:activity records of some participants, we found that their sleep:wake patterns were indistinguishable from a night shift worker. At first, we thought that these people forgot to identify themselves as shift workers. But after follow-up discussions, we realized that they were instead spouses of shift workers who had modified their daily lifestyle to be in sync with their partner.
Chronic jetlag – After traveling three time zones or more (east coast to west coast in the US), it can take up to a week for your circadian rhythms to be back to normal. As such, individuals that fly frequently and accumulate 100,000+ miles in a year (United 1K, Global Services, Oneworld emerald or Oneworld sapphire, Gold or Platinum medallions in Delta, MVP Gold 75K in Alaska air) are literally card-carrying chronic jet laggers and experience chronic circadian disruption. I have experienced this first hand. For ~8–9 months each year I fly at least twice a month, and that is enough to disrupt my rhythms. Being mindful of my patterns of sleep, physical activity, and food intake, I actively try to minimize the effects of frequent travel on my circadian rhythms, and therefore rarely fall sick. I also deliberately stop traveling 3 months each year so my body has enough time to rest and work efficiently.
Digital jetlag is when your body is in one-time zone but your mind is in another zone. How is that possible? This has been feasible only recently due to the widespread use of digital devices and connectivity that make it possible to work in real time with people living in a different time zone or to live-stream video content being generated across the globe. There is a completely new group of workers who did not exist a few decades ago. Those who live in one time zone but their working hours are tied to another time zone. This includes stockbrokers, financial analysts, call center workers, and a large number of IT professionals. Even if they are not classified as shift workers, the pressure to coordinate work with one or more colleagues working in a different time-zone disrupts their circadian rhythms. Similarly, entertainment and social network also disrupt our normal rhythms. We can now play video games or watch live games/concerts with individuals that are three or more time zones away.
Social Jetlag. Finally, the most unrecognized and most prevalent type of circadian disruption is social jetlag, which could affect > 50% of us. This type of jetlag happens when we stay awake past mid-night or have to wake up very early (e.g., 2 or 3 am) to finish an assignment, go clubbing, prepare for exams, etc., for one or more days in a week and then try to re-establish a normal routine on rest of the week. Nearly 70% of high school students, college students, young adults, and new mothers/dads stay up past midnight at least 1 day a week for an entire year, and therefore meet the definition of shift work or jet-lag. It’s as if they are in one time-zone on normal days, and a different time zone on the day they stay awake late into the night. This is no different from the schedule of someone doing night-shift work or traveling to a different time-zone. So, chronic diseases that are more prevalent among traditional shift workers may also affect us when we experience social jetlag.
As you can see, almost all of us fall into at least one of these categories (for at least some phases of our life), and these periods of circadian rhythm disruption adversely affect our health. These circadian-disruptive lifestyles increase our risk for disease in another way. To cope, we often develop bad habits (e.g., dependencies on coffee, tea, alcohol, energy drinks, or drugs to stay alert or to fall asleep). These may appear to be quick fixes, but they slowly become part of our daily routine. Some of these bad habits stay with us for the rest of our lives and contribute in their own ways to disease susceptibility.
http://blog.mycircadianclock.org/all-of-us-may-be-shift-workers-which-shift-worker-are-you/
