Why Working Nights May Raise Risk Of Obesity And Diabetes

"There are processes tied to the master biological clock in our brain that are saying that day is day and night is night and other processes that follow rhythms set elsewhere in the body that say night is day and day is night," said senior study author Hans Van Dongen, a professor in the WSU Elson S. Floyd College of Medicine. "When internal rhythms are dysregulated, you have this enduring stress in your system that we believe has long-term health consequences."

Although more research is needed, according to the team, just a few nights on a night shift schedule is enough to throw off protein rhythms that are related to blood glucose regulation, energy metabolism, and inflammation, all of which are processes that can influence the development of chronic metabolic conditions. They show that these disrupted rhythms can be seen as quickly as 3 days, and may even suggest that there may be a possible intervention for obesity and diabetes which could lower the risk of stroke and heart disease which is also elevated among night shift workers. 

For this study, volunteers were put on a simulated day or night shift schedule in a controlled laboratory setting for three days. Then after their last shift, the participants were kept awake for 24 hours while under constant conditions including lighting, temperature, posture, and food intake to measure their internal biological rhythms without interference from outside influences. During the 24-hour period blood samples were taken at regular intervals to analyze proteins present in blood-based immune cells. 

Some of these proteins had rhythms that were closely tied to the master biological clock that keeps the body on a 24-hour rhythm and is resilient to altered shift schedules, so they did not change much in response to the night shift schedule. However, most of the other proteins had rhythms that had substantially changed in the night shift participants compared to those in the day shift.

A closer look at proteins involved in glucose regulation revealed a nearly complete reversal of glucose rhythms among night shift participants. Processes involved in insulin production and sensitivity that work together to keep glucose levels within a healthy range were no longer working in synchronicity among the night shift workers. According to the researchers, this effect could be caused by the regulation of insulin trying to undo the glucose changes that were triggered by the night shift schedule. While this may be a healthy response in the moment, because altered glucose levels could damage cells and organs, it could be problematic over the long term. 

"What we showed is that we can really see a difference in molecular patterns between volunteers with normal schedules and those with schedules that are misaligned with their biological clock," said Jason McDermott, a computational scientist with PNNL's Biological Sciences Division. "The effects of this misalignment had not yet been characterized at this molecular level and in this controlled manner before."