Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, C25

Poster Communications

Is self-reported chronotype associated with caffeine intake in male night shift workers?

A. Koomson1, S. Lee1, M. Samy1, C. James-Harvey4, M. J. Morrell1,2,3

1. Clinical Research and Innovation Theme, Imperial College School of Medicine, London, United Kingdom. 2. Academic Unit of Sleep and Ventilation, National Heart and Lung Institute, Imperial College London, London, United Kingdom. 3. National Institute for Health Research Respiratory Disease Biomedical Research Unit at the Royal Brompton and Harefield National Health Service Foundation Trust and Imperial College London, London, United Kingdom. 4. Sleep and Circadian Neuroscience Institute, Oxford University, Oxford, United Kingdom.


Caffeine is a widely consumed psychoactive drug that increases alertness1. While moderate caffeine intake (<400 mg2) can prevent certain chronic diseases, chronic high caffeine intake increases cardiovascular risk factors such as blood pressure and cholesterol1. Working night shifts is associated with increased caffeine consumption3. Individuals' chronotypes (that which determines preference for day or night) can be categorised into ‘early lark', ‘intermediate', and ‘night owl'4. The aim of this study was to investigate if self-reported chronotype is associated with caffeine intake in male night shift workers. The study was carried out as part of a wider project to engage night shift workers, in collaboration with Sleep and Circadian Neuroscience Institute (SCNi), University of Oxford and Liminal Space. Night shift workers at a supermarket distribution warehouse were recruited. Self-reported chronotype was determined via a questionnaire provided by SCNi. Participants were then categorised as ‘lark', ‘intermediate', or ‘owl'. Consumption of caffeinated food and beverages (classified by the National Health and Nutrition Examination Survey5) over a 24-hour period from the end of 1 shift to the end of the next was determined by pictorial questionnaire developed by the research team for ease of use. Caffeine intake was then estimated using values made available by the Government of Canada2. Data was collected from 38 male night shift workers over 2 night shifts; approximately 200 staff were on duty per shift. 'Intermediates' (n=20) consumed the most caffeine, with 25% consuming more than the 400 mg recommended limit, but the difference between the 3 categories was not statistically significant. Duration of time working night shifts seemed proportionally associated with caffeine intake, with those having worked night shifts for longer consuming more caffeine than those who had recently begun working night shifts. The findings of this study suggest that self-reported chronotype is not associated with caffeine intake in male night shift workers. Duration of time working night shifts could be a better predictor of caffeine intake than self-reported chronotype, and follow-up studies should be performed to investigate this. In addition, association between genotypic chronotype and caffeine intake could be looked into. These studies could also be performed with the inclusion of female night shift workers. As night shift workers already tend to consume more caffeine than day shift workers, it is hoped that through these studies, public health messages could be tailored to sub-groups in the night shift worker population that may be especially at risk of consuming unhealthy levels of caffeine

Where applicable, experiments conform with Society ethical requirements