If you work evening or rotating shifts, you shouldn’t worry about having a higher risk of getting dementia or any psychiatric disorders. But if you have night shift work, particularly persistent (with 6 or more years of) night work, you have an increased risk of dementia, and several major psychiatric disorders, including mood, neurotic and substance use disorders. These are the conclusions of a PhD by Jeanette Therming Jørgensen. We are bringing a summary below. If you want the full report, do email her for a copy.

Increasing demand for a 24-hour society requires that more and more people work outside normal working hours, including at night. Shift work has been associated with various adverse health effects, yet biological mechanisms are not fully understood. Circadian disruption, sleep disturbances and psychosocial patterns are thought to play important roles in the link between shift work and disease development. Epidemiological evidence on adverse health effects of shift work, has typically focussed on somatic diseases, such as breast cancer and cardiometabolic diseases, while less attention has been given to potential effects on neurodegenerative diseases and mental health. Inconsistencies in the results, and substantial heterogeneity in the exposure definitions and outcome definitions, in existing literature on shift work and dementia, Parkinson’s disease, and psychiatric disorders, complicates overall evaluation of the evidence and calls for further research. 

The aim of this thesis is to examine the associations of shift work with neurodegenerative diseases and psychiatric disorders, using an epidemiological approach. Through linkage of questionnaire data from participants of the Danish Nurse Cohort to Danish National registers, the following disease endpoints were defined and examined in relation to shift work exposure; dementia (paper I), Parkinson’s disease (paper II) and mood, neurotic and substance use disorders as well as contacts to private practicing psychologist and psychiatrist with primary health care (paper III). 

In conclusion, the results of this thesis show that shift work, particularly persistent (with 6 or more years of) night work, is associated with an increased risk of dementia, and several major psychiatric disorders, including mood, neurotic and substance use disorders. We found no association between evening or rotating shift schedules with dementia or psychiatric disorders, except for suggestive association of evening shift work with mood and neurotic disorders. We found no association between shift work and Parkinson’s disease, and similarly we found no evidence of an association between shift work and contacts to private practicing psychologist or psychiatrist. We further present novel suggestive findings of which nurses who were most susceptible to adverse effects of shift work. Night shift workers with history of cardio-metabolic diseases seemed most susceptible to develop dementia. Night shift workers with history of psychiatric disorders were most susceptible to develop a new psychiatric disorder. Finally, full-time night shift workers were most susceptible to develop neurotic disorders.

If you want the PhD, do email Jeanette Therming Jørgensen to get it at jethe@sund.ku.dk.

Here are some links from the original studies:

Dementia paper, May 2020

Parkinson’s paper, Nov 2020

Psychiatric disorders paper, May 2021

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