Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science


Epidemiology and Biostatistics


Dr. Saverio Stranges

2nd Supervisor

Dr. Kelly Anderson



Shift work schedules are designed to maintain a continuous operation of goods and services. However, engaging in shift work may impact cognitive functioning. This thesis assessed the relationship between shift work and cognitive performance. Using cross-sectional data from the Canadian Longitudinal Study on Aging, multiple linear regression models were used to investigate the association between shift work and cognitive performance, as well as the moderating effects of psychological distress and sleep quality. Differences by sex and retirement status were also investigated. Shift work was significantly associated with poor performance for executive functioning but not for declarative memory. Poorer cognitive performance was found among completely retired and not or partly retired males. No evidence of a moderating effect by psychological distress or sleep quality was found. Our findings highlight important occupational health and safety implications. Future studies using a prospective cohort design is warranted.

Summary for Lay Audience

Shift work refers to work schedules which take place outside the regular work hours of 7:00 a.m. to 6:00 p.m. Commonly used shift work schedules include work shifts occurring early in the morning, afternoon, evening, or night. A person who works shift work may even alternate between different types of shifts on a weekly or monthly basis. As people with shift work schedules exhibit poor sleep and changes in their body’s natural sleep-wake cycle, research has linked the development of many long-term diseases to shift work, including cardiovascular disease, hypertension, diabetes, gastrointestinal conditions, cancer, metabolic syndrome, depression, or anxiety. Given the nature of shift work, negative changes to a person’s mental health, may also play a role in the development of disease among shift workers. Research suggests that shift work schedules may impair cognitive function, which are functions in the brain involved in learning, thinking, problem-solving, decision-making and memory. Not much is known about how a person’s mental health, specifically psychological distress -a state of emotional suffering- impacts this relationship. The purpose of this thesis was to examine the interrelationships between shift work, psychological distress, sleep quality and cognitive performance using survey data from a sample of Canadian adults aged 45-85 years. To assess cognitive performance, we assessed cognitive domains involved in problem solving (executive functioning) and long-term memory (declarative memory). We found that shift workers performed poorly on cognitive tests for executive functioning but not for declarative memory. Completely retired and not or partly retired male shift workers performed worse than female shift workers. We found that performances on cognitive tests among shift workers were the same regardless of the level of psychological distress or by the quality of sleep.