Effects Of Shift Work On Risk Of Chronic Diseases

In today's fast-paced world, the demand for a 24-hour society has increased exponentially. Economic and societal pressures have led to the emergence of a new working paradigm - shift work. For those of you working non-traditional hours, you might find yourself constantly fighting the urge to fall asleep throughout your shift, and struggling to fall and stay asleep once you’re off your shift. While shift work definitely poses great advantages to many industries, it is implied to have adverse long-term health effects on those who work this schedule.

Introduction

Definition of shift work

Shift work is defined as any work schedule that is not of the typical daytime schedule, which is between 9 AM to 5 PM. There are many different categories of shift work, such as night shifts, rotating shifts, weekend shifts, on-call shifts, and other non-day shifts. The core features of shift work in most people are commonly categorised as circadian misalignment (where sleep/wake cycles are not aligned with our ‘body clock’) , excessive sleepiness, and sleep disturbances.²

A brief overview of the effects of shift work on health

Shift work impacts our circadian rhythm, also referred to as our ‘body clock’, which syncs many different biological processes in our bodies. The main ‘master clock’ in our brain influences our sleep-wake cycle, and is mainly controlled by light. When working throughout the night, shift workers are exposed to light at odd times of the day, disrupting our natural sleep-wake cycle, and causing circadian misalignment.¹ This is classified as a sleep disorder called shift work sleep disorder (SWSD). Circadian misalignment leads to sleep deprivation and impaired alertness and performance. Recently, there have been multiple studies that showed shift work is associated with increased risk of chronic diseases and other health problems.²

Overview of chronic diseases

Definition of chronic diseases

Chronic diseases are health conditions that require ongoing management over a long period of time. They have persistent long-term symptoms, their effects may develop over time, and they cannot usually be cured. 

Types of chronic diseases

The most common types of chronic diseases include:

• Cardiovascular diseases (eg. hypertension, angina)
• Metabolic disorders (eg. diabetes)
• Gastrointestinal disorders (eg. ulcerative colitis, Crohn’s disease)
• Mental health disorders (eg. depression, anxiety)
• Autoimmune diseases (eg. rheumatoid arthritis, lupus)
• Respiratory diseases (eg. asthma, COPD)
• Cancers

Causes of chronic diseases

The causes of chronic diseases involve many factors and can include genetics, lifestyle, and environmental factors. Lifestyle factors such as tobacco use, lack of physical activity, and poor diet are significant contributors to chronic diseases.

The relationship between shift work and chronic diseases

Impact of shift work on specific chronic diseases

Shift work and cardiovascular diseases (CVD)

Numerous pathways have been identified that potentially connect shift work to CVD risk. Circadian disruption can lead to changes in metabolic and hormonal functions, causing stress a major risk factor for CVD. Along with an irregular sleep schedule, a higher prevalence of behaviours that lead to increased CVD risk, such as smoking and poor diet, are observed in shift workers.³ A study following people assigned female at birth (AFAB) night shift workers suggested that shift work is associated with a small but statistically significant increase in risk of coronary heart disease, but that this risk wanes over time after quitting shift work.⁴

Shift work and gut disorders

Light exposure at night and irregular eating times, which may be attributable to shift work, contribute to circadian rhythm disruption. This affects biological clocks around the body,which optimise many gut processes such as absorption of proteins, carbohydrates, and lipids, intestinal barrier functions, and maintenance of gut microbes. This dysfunction may in turn contribute to the development of gut disorders such as inflammatory bowel disease (IBD), peptic ulcers, gastroesophageal reflux disease (GERD), and colorectal cancer among others.⁶ 

Shift work and mental health disorders

One of the many functions of our ‘master clock’ is to control the hypothalamic-pituitary-adrenal (HPA) axis, a system which in turn regulates many biological processes, such as our stress response. It is believed that circadian disruption caused by shift work may lead to HPA dysregulation.⁸ This has several implications which leads to an abnormal response to stress, partly by inhibiting the brain’s reward system, and stimulating its fear system. Hence, shift workers may have difficulty managing physiological and mental responses to stressors, ultimately impacting emotional regulation and stress resilience.⁸  

Factors that may influence the relationship between shift work and chronic diseases

Age

Research has shown older shift workers are less likely to adapt to the circadian requirements of shift work.² This manifests in losing more sleep and reporting higher levels of sleepiness and sleep disruptions.² It is also suggested that as we age, changes in our brain may contribute to a shortening of our circadian rhythm, meaning older adults may have a preference to mornings, hence explaining their increased susceptibility to shift work disorder.⁹

Gender

Several studies suggest different phases of the menstrual cycle advance the rhythms of lowering core body temperature and lowering alertness towards the night, components which contribute to promoting sleep. It is also suggested that those AFAB experience a larger variation in alertness throughout the day, and since lower alertness is observed through the night - along with the advance in sleep promoting physiological changes, people AFAB are more likely to experience difficulty adjusting to night shift work.⁵

Duration of shift work

A study conducted in 2016 showed that the risk of developing chronic diseases, such as coronary heart disease, wanes with increased time since quitting shift work.⁴

Sleep quality

Shift work disrupts sleep patterns, leading to poor sleep quality, which is associated with an increased risk of chronic diseases such as cardiovascular issues, metabolic disorders, and mental health problems. Creating a conducive sleep environment and prioritising healthy sleep habits can help mitigate these risks for shift workers.

Prevention and management of chronic diseases among shift workers

Workplace interventions

Growing evidence of the association of shift work and chronic diseases have encouraged public health policies to revise shift work schedules. For example, the European Working Time Directive states that there should be at least 11 hours between shifts to allow for travel and sleep.¹

Lifestyle modifications

It is important to optimise the bedroom environment when resting to maximise sleep duration and quality, especially in the daytime. Avoid alcohol and caffeine close to bedtime, and maintain a cool, dark, and quiet sleeping area. Another strategy is to create a ‘sleep anchor’ schedule, where sleep periods overlap on both working and nonworking days. This helps regulate the circadian rhythm, improve sleep duration and quality, and also allows shift workers time for recreational activities on days off.² Involving your social group in your lifestyle modifications is also more likely to increase the success of your treatment plan and improve adherence and outcomes.

Treatment options

The American Academy of Sleep recommends shift workers take 3mg of exogenous melatonin before bed, but its effectiveness can be overridden by poor timing of light exposure .² Psychostimulants such as caffeine can increase alertness, but may reduce sleep quality and lose their effectiveness over time.²

Summary

Shift work is associated with developing chronic conditions such as diseases of the heart and gut, and is known to impact workers’ mental health.