Shift Work Symptoms Pt. 1: What is SWSD and How Does it Impact Your Health?

Published on March 08, 2017 by Chantal Ann Dumas

While shift work may be critical to the economy, evidence indicates that it can take a physical and emotional toll on workers. Let’s look at the facts surrounding shift work and explore some of the natural solutions to minimize their negative impact on our health.

What is Shift Work Sleep Disorder (aka SWSD)?
Shift Work Sleep Disorder (SWSD) is characterized by insomnia and excessive sleepiness affecting people whose work hours overlap with the typical sleep period. SWSD is frequently associated with falling asleep at work, a shortened total daily sleep time and a reduced sleep quality in comparison to those who work conventional day shifts.

The Numbers
Based on the 2005 Survey of Labour and Income Dynamics conducted by Statistics Canada, approximately 28% (4.1 million) of the 14.6 million employed Canadians work something other than a regular day shift. Rotating shifts and irregular schedules are the most common types of shift work, accounting for 2.3 million full-time workers approximately. While women made up approximately 37% of all full-time shift workers, they represent almost seven in 10 part-time shift workers.

In health-related occupation fields almost half of workers have a shift work schedule and two-thirds of those in protective services are shift worker. Those who work in sales and service-related industry are also more likely to work shifts.

Health Implications        


Overall, one third of full-time Canadian work force is working something other than a regular daytime schedule, with two-thirds of them working a rotating or irregular shift. This type of schedules is considered among the most difficult shifts because the body cannot properly adjust to the sleep pattern changes and health effects can be profound.

The most common health complaint of shift workers is lack of sleep. The 2005 Survey indicates that all shift workers were more likely to cut back on sleep when they needed more time in their day. According to several other studies, shift work has also been associated with cardiovascular disease, hypertension, and gastrointestinal disorders. Mental health disorders such as anxiety and depression have also been linked to shift work, and they can exacerbate conditions such as asthma, diabetes and epilepsy. In women, there is a net correlation between shift work and reproductive health problems and breast cancer.

How Does Shift Work Affect Our Health?
Researchers have proposed three potentially interrelated pathways that could provide an explanation for the association between shift work and health problems: disruption of circadian rhythms, adoption or worsening of unhealthy behaviour, and stress.

The Circadian Rhythms
Under normal conditions, our biological functions such as body temperature, cognitive performance and hormonal secretions follow a 24-hour cycle (known as our circadian rhythm), and science has clearly established the importance of keeping our internal body clock in sync with the rising and setting sun. However, shift workers often have to disrupt their circadian rhythms by being fully alert and ready to work when their bodies are preparing them for sleep, and vice versa creating what has been called a ‘chronodisruption’. Since, most shift workers return to normal schedules on their days off, the circadian system never gets a chance to fully adapt.

  • Melatonin Production 

One of the most ill effects of shift work on our health is the chronodisruption of melatonin production. Melatonin is a natural hormone produced by pineal gland activity in the brain that regulates the body's sleep-wake cycle. In addition to helping us fall asleep and bestowing a feeling of overall comfort and well being, melatonin has proven to have an impressive number of health benefits, including an array of anti-cancer properties. According to current scientific research, melatonin deficiency is associated with higher levels of inflammation, a weakened immune system, and an increased risk of cancer, particularly breast cancer. Based on signals of light and darkness, melatonin levels increase a few hours before bedtime when the body is preparing for sleep, it remains high at night, decreases in the morning, and remains very low during the rest of the day. When we are exposed to light at night, our brain interprets it as daytime and our biological clock instruct our pineal gland to immediately cease its production of melatonin. 

Unfortunately, whether we have the light on for a second or all night, the effect is the same. In most cases, the shift in the timing of the melatonin profile does not realign properly with night work and sleep during the daytime. This misalignment of the melatonin profile - and of the whole circadian cycle - contributes to disturbed daytime sleep, decreased alertness during night shifts, and presumably to many other health problems associated with shift work.

  • Melatonin and Breast Cancer 

Currently, the greatest area of melatonin research relates to breast cancer. Among the more impressive and well-known studies, the famous Nurses' Health Study published in 2001 revealed that nurses working the graveyard shift had 36% higher rates of breast cancer. When the body of epidemiological studies are considered in their totality, women who work night shift such as nurses and flight attendants are found to have breast cancer rates 60 percent above normal, even when other factors such as differences in diet are accounted for. Armed with this type of scientific evidences, the International Agency for Research on Cancer (IARC) – a branch of the World Health Organization – decided to classify shift work with circadian disruption or as a probable human carcinogen in October 2007.

In the second part of this blog, coming next week, we will discuss how to find a balance for your melatonin levels to help keep you healthy and alert for your next shift.