Glymphatic system, sleep, and shift work: a new paradigm in occupational and mental health?

Abstract

October 21, 1879, was a pivotal date that changed the world. That day, Thomas Edison created a light bulb that shone for 48 h straight. After that, mankind extended the working day into the night. The economic and social gains were remarkable, with a substantial increase in the number of jobs, but causing sleep loss and circadian misalignment due to shift work. Sleep medicine, a relatively recent field of study, has made extraordinary discoveries regarding the impact of sleep on the general human health, notably on occupational and mental health. Shift work is defined as a labor schedule that includes non-standard hours (especially evening and nighttime hours), performed constantly at a fixed schedule, at intermittent/rotating turns, or even according to less fixed time tables1. Changes in the natural sleep/wake cycle, also known as circadian rhythm, can trigger sleep disorders over the lifetime. There are many studies showing that sleep disorders negatively influence workers’ health, leading to conditions as hypertension, stroke, cardiovascular disease, diabetes, obesity, decreased immunity, cancer, anxiety, and depression2. A recent meta-analysis assembled the findings of 18 studies encompassing 18,802 workers exposed to shift working and compared to non-exposed controls. The results showed an unquestionable impairment in cognitive performance, by means of worsened working memory, processing speed, psychomotor vigilance, cognitive control, and visual attention3. The authors call attention to a deteriorated performance among shift workers, including work-related injuries as well as an increased risk of clinical and procedural prescribing errors by physicians. However, these findings go beyond a oneoff risk. A population-based study revealed inverted U-shaped associations between sleep duration and subsequent cognitive decline, as well with incidence of dementia4. This remark was confirmed by a robust recent meta-analysis elucidating the influence of sleep disturbances on the incidence of dementia, highlighting the importance of regular sleep5. Results of a prospective study of two cohorts indicate that mid-life shift work history, including nighttime work, was significantly associated with increased incidence of dementia in later life6. Furthermore, higher dementia risk was associated with a long shift work history. In the past