Out of rhythm: shift work as a cause of obesity

Tuesday evening, 21:00. Katrin S. is sitting on the packed underground train. The nurse is not on her way home after an after-work drink, but on her way to work. Today, her workday in a large Vienna hospital starts at 22:00 and will end at 6:00 in the morning. Katrin S. is working in a so-called alternating shift system, a common shift system in the hospital sector in which continued operations 24-7 have to be ensured. The shift schedules are usually organised in rotations of morning, late and night shifts. Like many of her colleagues, Katrin S. has been struggling to cope with obesity, an issue that has become increasingly serious ever since she has been working shifts.

Weight gain during shifts

“It is well-known that shift work leads to weight gain and therefore to an increase in the associated diseases, such as cardiovascular diseases, type 2 diabetes or cancers,” says nutritionist Karl-Heinz Wagner, coordinator of the Shift2Health EU project, “The concrete reasons for that have not yet been sufficiently explored. Are there certain physical parameters, differences between men and women, or differences between professions, such as in the healthcare or industrial sector? We strive to answer these questions in our large-scale European study.”

Between 600,000 and 700,000 people in Austria and 34 million employees across Europe are working shifts, which corresponds to around 20 per cent of the working population of Europe in total. “It thus affects roughly a fifth of the entire labour force. This is quite a large share and therefore it is crucial to investigate the impact of shift systems on the workers’ weight and overall health,” emphasises Wagner. 15 partner institutions in seven European countries – Austria, Italy, Germany, Poland, Denmark, the Netherlands and Belgium – are collaborating in this study, making it the largest Europe-wide study on shift workers to date.

Focus on the healthcare and industrial sector

The study will focus on employees both in the healthcare sector, which is dominated by women, and in the manufacturing industry, which is dominated by men. “By focusing on the healthcare sector and the manufacturing industry, we are able to cover a very wide area, in which shift work traditionally plays a major role. This is a key strength of our project,” says Katrin Scionti, project member at the Department of Nutritional Sciences of the University of Vienna.

The first major cross-sectional study will begin shortly: It investigates 1,000 employees in five countries (Austria, Germany, Poland, Denmark and the Netherlands) in total, half of which are working day shifts and the other half the night shifts.

“Study participants are happy that this project focuses on nursing staff and not, as usual, on the doctors,” explains project member Vanessa Schoissengeier from the Department of Nutritional Sciences. “Many nursing staff are overweight and want to change this. Most find it very difficult to lose weight due to the night shifts and their irregular meals. Many also observe that their general state of health has worsened ever since they have been working shifts.”

From eating habits to the microbiome

To gain a comprehensive overall picture, the study investigates a wide range of parameters. In addition to eating, sleeping and movement behaviour, the researchers also examine sensory perception, i.e. whether there are differences regarding the study participants’ taste preferences. Our project partners at the Charité hospital in Berlin are identifying the chronotype – does it make a difference whether shift workers are morning people or not? Furthermore, the researchers analyse markers related to inflammation, stress and metabolism, such as cholesterol and triglycerides.

“For all these parameters, we are also keen on finding out how they change over the course of a day or night shift. So, we take blood samples several times during the participants’ shifts,” explains Wagner. “The melatonin curve is interesting as well, that is the curve of the hormone regulating our day-night rhythm. Not only us researchers but also the participants have to do and deliver a lot over a study period of 1-2 weeks each.”

Another important parameter investigated as part of this project is the metabolic pattern. It comprises the characteristic metabolism properties of the entire organism as well as the so-called microbiome, that is the intestinal flora. We already know that it plays a major role in many areas of our health. “In this context, we cooperate closely with David Berry from CeMESS at the University of Vienna, one of the many fascinating collaborations in our project,” says Wagner.

The impact of nutrition

It is obvious that our mealtimes and the type of food we eat, both in general and in shift work, have an enormous impact on our weight and state of health. However, it has not yet been explored whether certain ingredients have an effect on our sleep-wake cycle with specific regard to shift work. An intervention study focusing on this topic is planned as part of the Shift2Health project: “We identify certain foods that might have an impact. For example, specific strains of microorganisms contained in yoghurt,” explains Wagner, “We identify certain ingredients, administer them in a targeted way and then investigate the various parameters in the shift workers participating in the study. It will be interesting to see whether and how we will be able to observe changes in their metabolism.”

The results of this large-scale EU project should directly benefit those affected, i.e. both the employees and the companies. “We are planning to develop a handbook containing recommendations for workers and companies, videos providing information about shift work, nutrition and exercise as well as workshops on the topic,” says Karl-Heinz Wagner about the intended output of the project, “Formulating new guidelines for shift workers at EU level is a major objective of this project, since there are no guidelines available for this group that could help them manage their nutrition and health.”