Two new studies have added to the evidence for a link between shift work and diabetes. One study examined whether those who work shifts are more likely to have diabetes, and included analysis of genetic information[i], and the other study looked at mice, in order to investigate how disruption of the body clock interacts with the effects of a high fat diet. The first study concluded that shift workers are more likely to have diabetes than non-shift workers, and the second study found that shift work can enhance the negative effect of a high fat diet on metabolic disorders, such as diabetes.
The study of diabetes risk and genetics used data from the UK Biobank. Associations of current and lifetime night shift work exposure with risk of type 2 diabetes were examined. Genetic data was available for 44,141 workers. Certain genes can increase the risk of type 2 diabetes, and the researchers assigned each participant a genetic risk score. Compared with day workers, all current night shift workers, whether they worked some night shifts or usual night shifts, were at higher risk of type 2 diabetes. The only exception was those who work night shifts exclusively. Considering a person’s lifetime work schedule, working more night shifts per month was associated with higher risk of type 2 diabetes. The association between genetic predisposition to type 2 diabetes and actually developing type 2 diabetes was not modified by shift work. This suggests that genetics and shift work are independent factors for type 2 diabetes, and that there is no interaction between the two factors. The researchers emphasise that this finding needs to be replicated in further studies.
The study of mice aimed to address the difficulty in determining cause and effect for the observation that shift workers tend to be at higher risk of disorders that can result from a fatty diet. It is difficult to determine whether the adverse health effects are caused by the shift work itself, or by the poor dietary habits that tend to accompany shift work, such as eating fatty food late at night. For the study, mice were fed a high fat diet and exposed to a light-dark cycle that offset by 12 hours every 5 days, to simulate 5 days of day work followed by 5 days of night work[ii]. Effects were observed in the immune cells of mice exposed to chronic shift cycling, and there was also exacerbation of diet-induced increases in body weight, insulin resistance and glucose intolerance. The researchers suggest that the mechanism by which these effects are enhanced by circadian disruption is related to how immune cells mediate inflammation.
‘We hope that we can find therapeutics to cancel out some of the problems caused by circadian rhythm disturbances’, said David Earnest, the lead researcher. ‘There are many people who are required to function well on irregular cycles, and if we can find a way to cut down the inflammation this causes, we may be able to minimize the long-term effects’.[iii]
[i] Vetter, C. et al. Night Shift Work, Genetic Risk, and Type 2 Diabetes in the UK Biobank. Diabetes Care dc171933 (2018). doi:10.2337/dc17-1933 http://care.diabetesjournals.org/content/early/2018/01/31/dc17-1933 (Accessed 27 February 2018)
[ii] Kim, S.-M. et al. Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high fat diet on inflammation and metabolism. The FASEB Journal fj.201700784R (2018). doi:10.1096/fj.201700784R http://www.fasebj.org/doi/abs/10.1096/fj.201700784R (Accessed 27 February 2018)
[iii] Untimely immune cell clocks may contribute to obesity and diabetes in shift workers. Science Daily. 6 February 2018. https://www.sciencedaily.com/releases/2018/02/180206090652.htm (Accessed 27 February 2018)