When darkness falls, sleep calls – except for the millions of shift workers who grind through the night. While the rest of us sleep, their health suffers.
Weight gain, diabetes, cancer, depression, and poor heart health are common among shift workers who are fighting against their body clock to stay awake when they should be sleeping; not to mention eating at times when their metabolism is normally winding down.
This misalignment wreaks havoc on a person's health as the body's normal circadian rhythms are thrown into disarray.
Research shows that when you eat has a real impact on health, and a new study in rodents has pinpointed one underlying mechanism that may drive changes in appetite when sleep-wake cycles and day-night cues don't line up.
A team of researchers from the University of Bristol in the UK investigated the link between hormones tied to sleep-wake cycles and daily feeding patterns in rats, and found disrupted circadian rhythms profoundly impacted the animals' eating behaviors.
The researchers disrupted the normal bodily rhythms of rats by giving the animals infusions of a hormone called corticosterone either in sync with or out of phase with light-dark cues.
Rats with normal rhythms were disrupted by ill-timed surges of corticosterone consumed the same amount of food each day as the in-sync animals and a control group of rats who received no infusions. But they ate almost half their daily food intake during times when they would otherwise be resting.
Although this altered timing wasn't associated with any weight gain or increase in fat mass, it was a huge departure from their usual feeding patterns – which the researchers traced back to greater activity at inappropriate times in genes that regulate appetite.
Rats with misaligned corticosterone levels had an uptick in the expression of several genes that produce proteins to stimulate appetite at times when those genes are normally switched off. This, combined with a lull in appetite-suppressing genes, likely led to an increased desire to eat significantly more during the inactive phase of the animals' day, the study found.
"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," University of Bristol neuroscientist and study author Stafford Lightman explains.
This is all great to know, but if it turns out that the same phenomenon occurs in humans, what could shift workers do to minimize the impact of their work schedules on their health?
Nurses, security guards and other shift workers know more than most how challenging it can be to follow the usual advice for countering the health downsides of their vital work: get some sunlight, squeeze in some exercise, and eat meals at regular hours.
There's good evidence for these recommendations: human trials – which are more informative than animal studies – have shown how confining meals to the daytime could help prevent mood disruptions associated with night work.
Time-restricted eating, which limits the hours when people eat but not necessarily the calories consumed, has also helped improve markers of cardiovascular health in a 3-month study of firefighters.
But as study author and endocrinology researcher Becky Conway-Campbell of the University of Bristol acknowledges, brain signals that drive increased appetite can be "difficult to override with discipline or routine".
So the team is designing studies to explore pharmacological therapies that could lessen disordered eating, based on what they know now about out-of-whack proteins stimulating night-time appetite.
Lifestyle strategies are in many ways preferable to medications, but they need to be feasible for people to implement.
"We hope our findings also provide new insight into how chronic stress and sleep disruption leads to caloric overconsumption," Conway-Campbell says.
The study has been published in Communications Biology.