The researchers reveal how certain circadian misalignment prevalent in night shift workers can profoundly alter the brain’s regulation of hormones controlling hunger to the detriment of metabolic health, by focusing on glucocorticoid hormones in the adrenal gland that regulate many physiological functions which includes appetite and metabolism. Glucocorticoids directly regulate a group of brain peptides controlling appetitive behavior with some being orexigenic (increasing) and some anorexigenic (decreasing) appetite.
Circadian misalignment is a phenomenon that is commonly associated with jet lag. Using animal models of out-of-phase jet-lagged and a control group, the team found that misalignment between light and dark cues led the out-of-phase group’s orexigenic hypothalamic neuropeptides (NPY) to become dysregulated, subsequently driving an increased desire to eat significantly more during inactive phases of the day.
According to the researchers, rodents in the control group ate 88.4% of their daily intake during their active phase and only 11.6% during their inactive phase; while rodents in the jet-lagged group ate 53.8% of their daily intake during their inactive phase, without increasing activity. This represents nearly 5 times more than the control group (460% more), showing that the rodent’s timing of consumption had been affected, revealing how disordered the neuropeptides become when glucocorticoid levels are out of sync with light and dark cues.
“For people working throughout the night, a reversed body clock can play havoc with their health,” said Dr. Becky Conway-Campbell, Research Fellow in Bristol Medical School: Translational Health Sciences (THS) and the study’s senior author. “For those who are working night shifts long-term, we recommend they try to maintain daylight exposure, cardiovascular exercise and mealtimes at regulated hours. However, internal brain messages to drive increased appetite are difficult to override with ‘discipline’ or ‘routine’ so we are currently designing studies to assess rescue strategies and pharmacological intervention drugs. We hope our findings also provide new insight into how chronic stress and sleep disruption leads to caloric overconsumption.”
“The adrenal hormone corticosterone, which is normally secreted in a circadian manner, is a major factor in the daily control of brain peptides that regulate appetite. Furthermore when we disturb the normal relationship of corticosterone with the day to night light cycle it results in abnormal gene regulation and appetite during the period of time that the animals normally sleep,” added Stafford Lightman, Professor of Medicine at Bristol Medical School: THS and co-senior author on the study.”Our study shows that when we disturb our normal bodily rhythms this in turn disrupts normal appetite regulation in a way that is at least in part a result of desynchrony between adrenal steroid hormone production and the timing of the light and dark cycle.”
“This is further evidence of how phase shift ‘jet-lag’ affects feeding behaviours and neuronal gene expression — data important for shift work comorbidity research,” said Dr. Benjamin Flynn, one of the study’s co-authors who conducted the study while at Bristol but is now based at the University of Bath.
