The research team also developed a genetic risk score for type 2 diabetes, examining genetic data for tens of thousands of workers in the database. They found that
‘The study finds that night shift work, especially rotating shift work including night shifts, is associated with an increased risk of type-2 diabetes and that the number of night shifts worked per month is associated to heightened risk.’
"We see a dose-response relationship between frequency of night shift work and type 2 diabetes, where the more often people do shift work, the greater their likelihood of having the disease, regardless of genetic predisposition," said co-first author Céline Vetter, Ph.D who conducted this work while at the Channing Division of Network Medicine at BWH, along with co-first author Hassan S. Dashti, PhD, RD. Vetter is now an assistant professor at the University of Colorado, Boulder. "This helps us understand one piece of the puzzle: frequency of night shift work seems to be an important factor."
The team examined data from more than 270,000 people, including 70,000 who provided in-depth lifetime employment information and a subgroup of more than 44,000 for whom genetic data were available. More than 6,000 people in the sample population had type 2 diabetes.
Using information on more than 100 genetic variants that are associated with type 2 diabetes, the research team developed a genetic risk score that they used to assign a value to each participant. As expected, those with the highest genetic risk scores were almost four times as likely to develop type 2 diabetes compared to individuals who had lower genetic risk scores. Shift work did not change this probability, suggesting similar effects of night shift work regardless of an individual's genetic predisposition to type 2 diabetes
The team found that, compared to day workers, all shift workers were more likely to have type 2 diabetes, except for permanent night shift workers
. Those who reported working irregular or rotating shifts with usual night shifts were 44 percent more likely to have type 2 diabetes, after taking into account other established risk factors.
"Our results suggest that these two risk factors both play a role in type 2 diabetes likelihood," said corresponding co-senior author Frank A.J.L. Scheer, PhD, Director of the Medical Chronobiology Program and neuroscientist in the Division of Sleep and Circadian Disorders in the Departments of Medicine and Neurology at BWH. "Our finding that there does not seem to be an interaction between those two type 2 diabetes risk factors is novel, and requires replication in future studies, especially in other populations of non-European ancestry."
The complete research is published in the journal Diabetes Care