Permanent night workers frequently have disturbed and insufficient sleep. Nevertheless, it is still unknown how night work affects the brain in the long term. Now research shows that permanent night workers more frequently develop dementia. Whether this results from disturbed sleep, changes in health behaviour or other factors is too early to say. The researchers believe that both employees and the employer can act to mitigate the potential health effects of night work.
When we sleep, our brain carries out important cleaning tasks. Sleep plays a vital role in storing experiences and information in our memory. New research shows that, during sleep, the body removes waste products that have accumulated over a long and active day, so the brain is ready to store new information the next day. Sleep deprivation has previously been shown to impair memory and reaction time. Now, a new study using Danish data shows that night work may also have long-term effects.
“Our study shows that permanent night workers develop dementia more frequently than permanent day workers. Initially, we had expected to observe dementia more frequently in all types of shift work including night shifts. Nevertheless, the study suggests that this only applies to permanent night workers. Our results show that these people could be a relevant target group for preventive efforts so that they can have a healthier life in older age,” says a main author, Kirsten Nabe-Nielsen, Associate Professor, Section of Social Medicine, Department of Public Health, University of Copenhagen.
All or nothing
This is not the first time the relationship between shift work and dementia has been studied, but the results of the few previous studies are inconsistent. The researchers therefore wanted to examine the association between shift work and dementia by clearly distinguishing between shift work with and without night work. The Danish Work Environment Cohort Study enabled them to do this. The study, conducted in 1990 by the National Research Centre for the Working Environment, included a random sample of 9700 people 18–59 years old drawn from Denmark’s Central Population Registry. The new study included all participants who turned at least 60 years old during the follow-up period, which lasted until the end of 2016.
We used survey data on working hours and linked them to registry data on dementia to compare information on working hours for more than 3000 people with the number of dementia cases. We found 85 people with dementia, and the risk of dementia was significantly higher among permanent night workers than among permanent day workers. Actually, we were surprised that employees working night shifts combined with other types of shifts did not develop dementia more frequently.
The researchers had expected an incremental effect, so that people who worked night shifts once in a while would develop dementia slightly more frequently and permanent night workers would develop dementia the most frequently.
“If lack of sleep causes dementia to develop, a dose–response relationship would probably be expected. But this relationship is more all or nothing. If you always work at night, you have a higher risk, but if you only occasionally work at night, you have the same risk as everyone else.”
Stress and social relationships
It is still too early to draw conclusions on what causes the observed associations, especially because night shift work can co-occur with several other risk factors for dementia. Night shift work as a cause of dementia should thus be distinguished from night shift work as an indicator of a greater need for guidance and support among a specific group of employees. For example, this could include advice on how to optimally take care of oneself when working permanent nights.
”We cannot exclude that duration of education and unhealthy lifestyle play a role in the association between night shift work and dementia, and we took these factors into account in our study to the extent the data allowed. As a researcher focusing on working hours, my colleagues and I colleagues are investigating the health risks causes by shift work, and I would therefore obviously prefer to elucidate causal relations. But this does not change the fact that society depends on some people choosing jobs that involve night shift work. It is therefore also important to think about how we can help people working night shifts.”
The researchers are continuing to investigate exposures in the working environment that may increase the risk of dementia. The exposures examined in the MEMORIA project include serious conflicts, social relations and stress. The hope is to provide both employees and managers with new knowledge that can ensure better and healthier lives.
”We know that many of the factors associated with the risk of cardiovascular disease are also associated with the risk of dementia. This is how we should think about preventing dementia, because what is healthy for the heart is also healthy for the brain. For night shift work, carrying out preventive efforts in collaboration between employees and employers is extremely important. Regardless of whether the higher frequency of dementia results from night shift work or other factors not related to work, this target group could benefit from support. This could include advice and guidance on health behaviour changes and sleep hygiene, but also concrete offers such as help in quitting smoking, healthy diet and exercise facilities at work.”
“Night shift work, long working hours and dementia: a longitudinal study of the Danish Work Environment Cohort Study” has been published in BMJ Open. The project was carried out with support from the Danish Working Environment Research Fund. In 2018, the Novo Nordisk Foundation awarded a Challenge Programme grant to a co-author, Rudi Westendorp, for the project Harnessing the Power of Big Data to Address the Societal Challenge of Aging.