Poor sleep, eating at night drive cardiometabolic risks in circadian misalignment
Night-shift workers and other adults who sleep primarily during the day are at increased risk for diabetes, obesity and cardiovascular disease, but the underlying mechanisms are not well understood.
One potential mechanism for this increased risk is circadian misalignment, which occurs when an individual performs actions that run contrary to the body’s circadian clocks, such as sleeping during the day and eating during the night, according to Andrew McHill, PhD, research assistant professor in the Oregon Institute of Occupational Health Sciences at Oregon Health and Science University.
“We have little peripheral clocks, or little circadian clocks, throughout the body that are promoting optimal timing for things,” McHill told Healio. “When you’re doing things at nonoptimal times, such as sleeping during the day or being awake and eating at night, you’re misaligning those things. It leads to a whole host of issues because your body isn’t prepared for it.”
Researchers have identified impaired sleep quality and eating at inappropriate biological times as two possible mechanisms behind the association between circadian misalignment and poor health outcomes. However, whether sleep or food is a primary driver, and the details behind each of these mechanisms, is still debated.
“Up until now, most studies have examined the impairments associated with sleep and circadian disruption,” Josiane L. Broussard, PhD, assistant professor and director of the Sleep and Metabolism Lab at Colorado State University, told Healio. “A handful of studies have looked at tissue-specific changes, but no one has identified a [primary] mechanism.”
Impaired daytime sleep quality, duration
Proper sleep duration and quality are difficult to achieve for individuals experiencing circadian misalignment due to the body’s day-night cycle and the way it reacts to light, according to Broussard.
“We know that shift workers and people who are subjected to circadian rhythm misalignment will have shortened sleep duration and also reduced sleep quality,” Broussard said. “Sleep in the daytime is going to be inherently lower quality sleep for a lot of different reasons.”
One way night-shift workers might combat poor sleep is by matching their light exposure to mimic working in the day and sleeping at night using artificial light and blackout curtains. However, McHill said, the body’s internal circadian clock’s drive to be aligned with the natural light-dark cycle of the time zone in which you live and makes perfect sleep quality difficult to achieve when out of alignment.
“Even if we put you in an environment where we control the temperature, make it perfectly quiet and dark, and keep you awake all night, trying to sleep during daytime hours results in only about 70% of what you sleep during the night,” McHill said.
Sleep plays an important role in metabolism, and poor sleep can reduce insulin sensitivity.
That is one reason researchers said they believe that circadian misalignment increases the risk for diabetes, according to Broussard. However, more research is needed to determine the nature of the link.
“We don’t know why sleep loss impairs insulin sensitivity,” Broussard said. “We know it can be induced quickly, so even just one night of sleep loss will significantly impair insulin sensitivity in humans, in dogs, in rodents. But we don’t know why or how.”
Timing of meals and energy expenditure
In addition to the promotion of sleep and wakefulness at certain times of the day, internal circadian clocks also cause the body to react differently to food and energy expenditure at different times of the day, according to McHill.
“The way your body responds to what you eat differs based on the time of day,” McHill said. “Say you eat a cookie during the day, your body is going to respond such that you’re going to have increased energy expenditure to metabolize the cookie. If you were to eat that same cookie during the nighttime hours, you won’t expend as much energy to break down that cookie, and you will begin to store [the energy] throughout the body.”
Complicating the relationship, external factors may influence what is eaten during circadian misalignment. The lack of available healthy food at night may have a negative impact on night-shift workers.
“People have less access to healthy foods overnight,” Broussard said. “For example, the cafeteria may be closed and if you’re not packing your own food, you may only have the vending machines to go to.”
Expending less energy means more fat is stored in the body. McHill said although the body can respond adequately to infrequent late-night meals, regularly eating during the overnight hours could eventually increase risks for poor health outcomes.
“We see this a lot in shift workers,” McHill said. “[Shift work is] associated with higher rates of obesity, insulin insensitivity and CVD. You start to see that CVD increased risk start to occur about 5 years after working shift work.”
Circadian misalignment drivers
The question of whether eating or sleeping is a primary driver for poor health outcomes in circadian misalignment is being explored. Broussard said some research is taking a closer look at how circadian misalignment causes changes at the cellular and molecular levels.
“Research has started to look at these tissue-specific changes,” Broussard said. “Even though [poor sleep and poor nutrition have] big, all-system impacts, there are also tissue-specific effects. We have done studies that have taken fat and muscle biopsies and also see changes at the molecular level in response to sleep disruption.”
Other ongoing research is exploring how to improve health outcomes for night-shift workers. McHill said some current studies are analyzing the timing of eating and increasing physical activity to combat lower energy expenditure at night.
“Some ideas that are currently being tested are to try to keep the majority of your calories, or your food intake, on the bookends of a shift if you’re working shift work,” McHill said. “Eat a higher amount before you start your shift and a higher amount at the end. Try to match it the most with your internal body clock’s daytime as you possible can. Then have small-calorie snacks during the shift if you need anything. Another one that’s being tested is to try to increase activity levels to try and combat that lower energetic response to meal timing. These are studies that are currently being investigated, so it will be very interesting in the next couple of years to see how they come out.”
McHill said the best way for individuals to address circadian misalignment is to be more aware of late-night behaviors.
“We often do things at times that we’re really not supposed to,” McHill said. “Especially with electric lighting, we can stay up later and watch television and have snacks. I hope people can be cognizant of not taking that type of thing for granted. Consider sleep and the timing of activities just as important as what you eat and how much you exercise. ... We can really work to be a healthier population.”