Night shift work characteristics are associated with several elevated metabolic risk factors and immune cell counts in a cross-sectional study.

Night shift work is associated with increased health risks. Here we examined the association of metabolic risk factors and immune cell counts, with both night shift work and particular characteristics thereof: frequency, duration and consecutive night shifts. We performed a cross-sectional study using data from 10,201 non-shift workers and 1062 night shift workers of the Lifelines Cohort study. Linear regression analyses, adjusted for demographic, lifestyle and occupational factors, were used to study associations of night shift work characteristics with metabolic risk factors and immune cell counts. Night shift workers had an increased BMI, waist circumference and immune cell counts compared to non-shift workers. This was especially seen in night shift workers who had a higher frequency of night shifts per month (≥ 5: BMI: B = 0.81 kg/m (95%-CI = 0.43-1.10); waist circumference: B = 1.58 cm (95%-Cl = 0.34-1.71; leukocytes: B = 0.19 × 10 cells/L (95%-CI = 0.04-0.34 × 10)) and worked more consecutive night shifts (> 3: BMI: B = 0.92 kg/m (95%-CI = 0.41-1.43); waist circumference: B = 1.85 cm (95%-Cl = 0.45-3.24); leukocytes: B = 0.32 × 10 cells/L (95%-CI = 0.09-0.55 × 10)). This association was less pronounced in long-term night shift workers (≥ 20 years). Our findings provide evidence for the association between night shift work characteristics and BMI, waist circumference and leukocytes (including, monocytes, lymphocytes, and basophil granulocytes).