Working nights can throw your sleep, diet, exercise, and social life out the window — after all, how do you get coffee with a friend if all your friends are asleep? But the graveyard shift doesn’t just force a lifestyle change. It may also change your body’s metabolic health.
This isn’t just an observed phenomenon. Controlled human studies suggest “circadian system and circadian misalignment have distinct influences on glucose tolerance, both separate from the behavioral cycle.” This biological reality intersects with demographics, like race, ethnic background, and class: People who work at night are more likely to have lower incomes and more likely to be from racial or ethnic minorities. These populations also tend to have worse health outcomes on average.
But a study recently published in Science Advances may be a way to mitigate some of the ill effects an out-of-whack circadian rhythm wreaks on the body.
What is circadian rhythm?
Our circadian rhythm is basically our body’s internal clock — but it’s a more fundamental part of our complex biology than you might imagine. Essentially, circadian rhythm is like a clock that ticks in every cell in the body, and each cell’s clock’s timing is governed by a master clock in the brain, but they can also keep ticking without the brain getting too involved.
An easy way to see this in action is to consider your daily diet: Our body expects to eat at certain times, and it sends out cues to prompt us to eat and fuel it back up. Humans are daytime creatures — we're not nocturnal, like owls. So the middle of the night isn’t one of the times the body expects to refuel — that’s when we are supposed to be asleep.
The problem with eating at night
One of the consequences of eating when our body expects us to be asleep is impaired glucose tolerance — that means the body can’t process sugars correctly. When someone has impaired glucose tolerance, the level of glucose (sugar) in their blood rises, but it doesn’t reach the threshold for diabetes, which is a chronic condition characterized by there being too much sugar in the blood and an inability to use glucose as fuel for the body.
While impaired glucose tolerance is not diabetes, people with this issue are at a much higher risk of developing diabetes and cardiovascular disease than the general population.
Sarah Chellappa, a neuroscientist at Brigham and Women's Hospital in Boston and lead author on the recent Science Advances study explains a little about how this works on the cellular level:
“Animal work suggests that such negative effects may be due to a misalignment between central and peripheral ‘clocks’ — natural body timekeepers that control physical and behavioral changes over the 24-hour cycle. Hence, the effects of nighttime eating on glucose tolerance might be due to the misalignment of such central and peripheral ‘clocks.’”
To test this idea, Chellappa and her colleagues conducted an experiment involving 19 people who lived for 14 days in a lab.
The discovery — In this unconventional experiment, 12 men and seven women spent two weeks living in a lab.
First, the researchers assessed the participants’ baseline circadian rhythms under constant behavioral and environmental conditions. To do this, the participants were kept awake for 32 hours in a dimly lit room, eating hourly snacks.
This fairly terrible-sounding element of the experiment serves an important purpose, Chellappa explains.
“The Baseline Constant Routine protocol was used to assess endogenous circadian rhythms in the absence of masking effects, such as light exposure, posture, meals, physical activity, changes in environmental temperature, to name a few.”
These factors can mask our endogenous —or fundamental— circadian rhythms, and as a result, it can be hard to know our true endogenous circadian rhythms.
“Because the laboratory constant routine protocol controls for all these behavioral and environmental factors, we can say that an observed rhythm of, for example, glucose, is actually a true circadian (glucose) rhythm,” she explains.
After that, the researchers tried to simulate working at night in the lab. The participants were put on a schedule of 28-hour long “days” — the idea was to put the participants 12 hours out of sync compared to the first day.
Then, the participants were sorted into two groups:
- The nighttime meal control group — this group ate at least one meal at night, as a worker typically would when doing night shift work.
- The daytime meal intervention group — this group didn’t eat during the course of their “night” but instead kept their meals to the daytime.
At regular points, the participants’ body temperature, glucose, and insulin levels were checked.
All the participants had circadian misalignment — they were awake all night, after all — but the difference in glucose rhythms between the two groups was striking.
For the people who ate during the day, there was no significant change from the baseline they established early in the study. But the glucose profile of the group that ate both during the day and at night increased by 19.4 percent (as compared to baseline).
What this suggests is that eating during the day may counteract some of the side effects of working at night on the body’s metabolic health.
“[We didn’t expect] that limiting meals to the daytime didn’t just improve glucose tolerance and circadian alignment, but could completely normalize both aspects, despite still following a night work protocol where they were awake at night and slept during the day,” Cheppalla adds.
How to stay healthy on the night shift
Ultimately, Cheppalla and her team’s research could help workers counteract the negative health effects that are tied to the night shift, like diabetes and glucose intolerance.
“The study’s take-home message is that daytime eating, despite mistimed sleep, aligns central and peripheral rhythms and prevents glucose intolerance,” Chellappa says.
“While more research needs to be carried out to develop practical interventions to implement daytime eating in real-life shift workers, our findings are an important breakthrough in the development of interventions to help maintain appropriate glucose tolerance in night workers.”
Having a better understanding of how the night shift affects health — and ways to mitigate those harms — is vitally important.
That said, it is a tall order to ask people who work all night to also not eat during that period — something the researchers acknowledge.
“Our study aimed at answering fundamental research questions, and because of that the type of study design used limits a direct translation of the meal schedules to real-life shift work,” Chellappa says.
“We need practical interventions to implement daytime eating in night workers, without disrupting their sleep and daily activities. While these practical approaches still need to be established, it may be helpful for night workers to consider limiting the amount of food (particularly carbohydrates) they eat in the nighttime,” she says.
“Shift workers with Type 2 diabetes or other comorbidities would best do this in concert with their physician,” she adds.
Abstract: Night work increases diabetes risk. Misalignment between the central circadian clock and daily behaviors, typical in night workers, impairs glucose tolerance, likely due to internal misalignment between central and peripheral circadian rhythms. Whether appropriate circadian alignment of eating can prevent internal circadian misalignment and glucose intolerance is unknown. In a 14-day circadian paradigm, we assessed glycemic control during simulated night work with either nighttime or daytime eating. Assessment of central (body temperature) and peripheral (glucose and insulin) circadian rhythms happened during constant routine protocols before and after simulated night work. Nighttime eating led to misalignment between central and peripheral circadian rhythms and impaired glucose tolerance, whereas restricting meals to daytime prevented it. These findings offer a novel behavioral approach to preventing glucose intolerance in shift workers.