The night-time economy contributes £93.7bn annually to the UK economy(1) and relies on extensive employment of night workers. The association between night work and adverse cardiometabolic health is of increasing concern. Shift workers, compared to day workers, are more likely to be diagnosed with type 2 diabetes (T2D)(2) and shift workers living with T2D are reported to have higher glycated haemoglobin compared to day workers(3). Simulated shift work studies have significantly contributed to understanding how eating at night impacts physiology however, real world research is needed among shift workers. The Shift-Diabetes study (ISTCTN 11764942) is a mixed methods study with the aim to characterise current management of T2D in shift workers.
An observational study was conducted in 40 shift workers (working a combination of night and day shifts) living with T2D. Across 10-days, data was collected on blood glucose (continuous glucose monitor), diet (self-report diary), sleep and physical activity (actigraphy). The monitoring period covered night shifts, day shifts and rest days. Within person mean glucose concentration (MG), coefficient of variation (CV), mean absolute glucose (MAG), mean amplitude of glycaemic excursion (MAGE) and dietary intake (food choices, nutrient intake) were compared between ‘behavioural day’ types. A ‘behavioural day’ was defined as the period between two main sleep periods (sleep off set to sleep off set)(4) Figure 1. Behavioural day types were categorised as: night shift, day shift, rest after night shift and day off. A parallel qualitative study was conducted in 15 shift workers using semi-structured interviews to explore barriers and enablers to dietary behaviour during shift work(5).
The study sample was predominantly female (89.2%) and employed as a nurse or midwife (62.2%). The behavioural day duration was significantly longer when a night shift was worked (26.9 SD2.5hrs) compared to a day off (23.5 SD1.0hrs, p<0.001). A rest after night shift day was shorter than all other day types (17.2 SD2.7hrs, p<0.001). Energy intake (%) from confectionary was higher on a night shift compared to a rest after night shift (13.4 SD12.0% vs. 7.8 SD11.8%, p = 0.013). Caffeine intake was significantly different across all day types, except between day off and day shifts, with intake highest on night shifts (164.8 SD175.5mg/day). There were differences in the number of eating occasions, with night shifts having the highest occasions (7.0 SD2.2) and rest after night the lowest (3.4 SD1.6). No differences were observed for MG, MAGE or CV. MAG was higher for night shift compared to rest after night shift (3.4 SD1.0 vs. 2.9 SD1.6, p = 0.029). The qualitative study found shift workers wanted to make healthier food choices during night work but were inhibited due to limited access to food and a lack of confidence in adjusting diet intake to shift schedules(5).
The duration of behavioural day when dictated by type of shift can vary significantly and may impact dietary intake and blood glucose. Further research to understand how changes in behavioural day duration impact shift worker behaviours and health are needed.
King's College London BDM Research Ethics Subcommittee (HR-19/20-14630)