Shift work is associated with an increased risk of negative mood disorders, which is partially attributable to associated lifestyle changes. A new study published in JAMA Network Open discusses the contribution of lifestyle factors in depression and anxiety among shift workers.

Study: Lifestyle factors in the association of shift work and depression and anxiety. Image Credit: PeopleImages.com – Yuri A / Shutterstock.com

Introduction

Currently, depression and anxiety affect over 320 million and 260 million people, respectively. These conditions increase the risk of disability and early death, thus making it important to identify and intervene appropriately to mitigate the effects of the primary and secondary risk factors for the development and progression of these conditions.

Shift work refers to work outside normal working hours, such as early in the morning, late in the afternoon, or at night. Multiple health issues have been linked to this phenomenon, including cardiovascular and mental disease.

Prior research has often ignored the contribution of the type, frequency, and duration of shift work, as well as confounding factors such as the weekly work load and work intensity. Lifestyle behaviors may also contribute to mood disorders.

The study data was obtained from the United Kingdom Biobank survey baseline data, which were collected between 2006 and 2010. The study cohort comprised over 175,000 working people equally reflecting both genders, with all data analyzed between November 2022 and January 2023.

What did the study show?

The vast majority of the study cohort were White, with less than 5% being of other racial origins. The mean age was about 53 years, with about 16% of the cohort identifying as shift workers.

Follow-up results were obtained over a median of nine years, in which a 2% incidence of depression and anxiety was reported each, with depression more frequently reported than anxiety. After considering other factors, the risk of depression and anxiety among shift were was 22% and 16% higher, respectively.

The risk remained comparably increased among those who occasionally or sometimes worked shifts and habitual shift workers. The risk was higher as the frequency of shift work increased; however, the timing of the shift did not impact the risk of depression or anxiety. The longer the duration of shift work in terms of number of years, the lower the risk of these mood disorders.

The main lifestyle factors impacting the risk of depression and anxiety included smoking, time spent in sedentary activity, body mass index (BMI), and sleep duration. These factors contributed about 33% and 20% of the risk for depression and anxiety, respectively.

Sleep deprivation, current smoking, sedentary time, and BMI accounted for about 8%, 7%, 1.6%, and 15%, respectively, of the association between depression and shift work. Comparatively, for anxiety, these factors contributed about 6-7% each for sleep duration and current smoking, whereas BMI mediated about 8% of the association.

Demographic factors such as age, sex, socioeconomic status, and the hours of work did not affect this association, with the striking exception of heavy manual labor. Individuals who rarely or never performed these tasks were at a nearly 50% and 40% greater risk of depression and anxiety, respectively. Even occasional heavy manual labor reduced the risk to nearly normal levels for anxiety and only 8% higher for depression.

The reduced incidence of these mood disorders with increasing duration of shift work in years could reflect better adaptation to the job. The greatest stress due to fatigue occurs at the beginning of shift work and is linked to greater mental distress at that time. As the worker gains skill and confidence, fatigue decreases with an accompanying restoration of mental health.

Earlier studies have shown an increased risk of mental illnesses with night shifts, unlike the current paper, which requires further elucidation. This may be due to variations in the start and end points of a night shift.

Interventions targeting smoking, sleep hygiene, control of body mass, and the time spent in physical activity could modify the risk of shift work to mental illnesses. This is the largest study to date wherein researchers identify the correlations between mental health and shift work, and the potential routes of association.

What are the implications?

The well-known adverse outcomes of shift work motivated the researchers of the current study to assess the association of these jobs with an increased risk of anxiety and depression, while also considering the potential role of lifestyle factors.

These findings suggest that the development of public health interventions related to the promotion of healthy lifestyles may improve the mental health of individuals who reported shift work.”