Shift work is a well-known risk factor for the development of overweight and obesity, which may lead to downstream effects such as increased risk of cardiometabolic diseases and cancer. However, the biological and behavioral mechanisms underlying the obesogenicity of night shift work are not well understood. Population-based mechanistic studies in real life shift workers are needed to address how night shift work impacts metabolic health.

The investigators aim to characterize the behavioural, environmental, and biological mechanisms and pathways for the association of night shift work and obesity across Europe.

The investigators will conduct a cross sectional study in 5 European countries (Austria, Denmark, Germany, Netherlands and Poland) and recruit 1000 rotating night shift workers and day workers (200/country) from the health sector and different industries. Night and day workers will be age-frequency (3 age groups), gender and (where possible) working tasks matched. Participants will complete online questionnaires and report their diet habits in a mobile app. Body composition, dietary behavior and sensory preferences will be tested. Biologic specimens (blood, urine, saliva, hair and feces) will be collected at the workplace on a day where participants are working on a day shift (or a day off). In a subsample (Austria and Netherlands) shift workers will provide biological samples (spot blood, urine and saliva) both on a day shift and on a night shift. Biomarkers including hormones, cellular immunity and inflammation, parameters linked to gut health and metabolism of fat and sugar, appetite, oxidative stress, metabolomics and microbiota will be measured. The investigators hypothesize that compared to day workers, night shift workers will experience disrupted levels of pre-obesity markers. Higher circadian disruption, sleep disruption and mistimed eating patterns workers will be associated with more disrupted biomarker profiles. Among rotating shift workers, night shift will be associated with acute disrupted melatonin production, metabolomic profiles and composition of oral microbiota compared to a day shift.

Inclusion Criteria shift worker

• Health care sector or industrial shift worker
• Employed or self-employed
• 21 years or older
• ≥ 24 h/ week
• Shift work duration > 3 years and currently doing night shifts
• 4 or more rotating night shifts/month (night shift defined as a work schedule that involves working at least 3 hours between 00:00 and 5:00), at least 2 consecutive nights/month

Inclusion criteria controls

• Health care sector or industrial work
• Employed or self-employed
• 21 years or older
• ≥ 24 h/ week
• No night shift or rotating shift work in the last 5 years
• No history of night shift or rotating shift work for more than 5 years

Exclusion Criteria shift worker and controls:

• Pregnancy
• Lactation period
• BMI of 40 kg/m2 or above
• Present treatment of a disease e.g. cancer radio- or chemotherapy
• Chronic diseases if in an ongoing therapy but not after a remission (renal failure, active hepatitis, cirrhosis, myocardial infarction, chronic obstructive pulmonary disease and cancer)
• Immunodeficiency syndrome, any auto-immune or auto-inflammatory diseases (e.g. type-1 diabetes, multiple sclerosis, lupus, rheumatoid arthritis) and acute episodes of atopic diseases (atopic dermatitis, asthma, type 1 allergies such as hay fever)
• Bariatric surgery
• Antibiotics in the last month

We are recruiting shift worker and day worker in the industrial and healthcare setting.