Changing your sleep schedule even slightly — like going to bed at 10 p.m. on weekdays, then at 11:30 p.m. on weekends — could potentially be linked to harmful gut bacteria that contribute to obesity and cardiovascular disease, according to a recent study.
The study, published Aug.2 in The European Journal of Nutrition, found that irregular sleep patterns caused by social jet lag (your body adjusting to a chronic shift in sleep patterns), may be linked to diet quality, inflammation and the makeup of your gut microbiome.
“We know that major disruptions in sleep, such as shift work, can have a profound impact on your health,” Wendy Hall, a registered nutritionist at King’s College London and author of the study, said in a press release.
“This is the first study to show that even small differences in sleep timings across the week seem to be linked to differences in gut bacterial species.”
There is a diverse community of microorganisms, like bacteria, viruses, yeasts and fungi, living in the human gut that are essential to human health. Disruptions in these microbiomes can have severe health impacts, explained Patricia Lakin-Thomas, professor of biology at York University in Toronto.
“We’ve only recently discovered how important they are and how they affect not just our digestion, but all kinds of other things in the body. We don’t really understand how they do that, but we’re finding these correlations … even impacts on mental health,” she said.
And sleep may be another piece of the puzzle.
How the sleep study worked
In order to find how social jet lag may affect gut bacteria, the researchers from King’s College London in the U.K. analyzed a sample of 934 participants from the United Kingdom between June 2018 and May 2019. They collected and studied blood, stool and gut microbiome samples, along with glucose measurements, comparing people with irregular sleep patterns with those with a routine sleep schedule.
They found that even a 90-minute difference in the timing of the midpoint of sleep (the halfway point between bedtime and wake-up timing) may be associated with differences in a person’s gut microbiome.
For example, three out of the six microbiome species that were more significantly present in the social jet lag group were found to have “unfavourable” links with health, the study found. These microbes are associated with poor diet quality, obesity and higher levels of inflammation and cardiovascular risk.
The researchers found that the social jet lag group was also more prone to having a poor diet, a higher intake of sugar-sweetened beverages, and lower intakes of fruits and nuts, which may influence the abundance of specific microbiota in someone’s gut.
Although the study found a correlation between social jet lag, poor nutrition and unfavourable gut health, the researchers could not find causation.
“This study looked at the association between social jetlag and microbiome composition so we can’t point to the exact cause,” Kate Bermingham, a postdoctoral researcher in nutrition at King’s College London and lead author of the paper, told Global News in an email.
“The data does suggest that the shift in sleep alone is having an impact but more studies to understand the details on other factors are needed to confirm the causal pathways.”
The researchers noted that some people, such as teenagers and young adults, are also more susceptible to social jetlag, as many are “biologically programmed” for later bedtimes and wake times. But they added that modern lifestyle factors, like screens emitting blue light, and work schedules also disrupt people’s natural sleep patterns.
'Some weakness' in the study
Lakin-Thomas argued that although the researchers found a correlation between the microbiome and social jet lag, the science behind gut health is still so new that it’s difficult to link specific microorganisms to someone’s heath.
“So they (the researchers) have a kind of a weak correlation where they’ve been able to explain some of the health outcomes with some of the changes in the gut microbiome. But I don’t think it’s a particularly strong study. I think there are some weaknesses,” she said.
For example, she criticized the study’s grouping of social jetlag, which was 90 minutes or more sleep disruption.
“They’ve made an arbitrary cutoff, and just said anybody who’s got more than one and a half hours of social jetlag will lump them all in one category,” she argued.
“So it’s probable that people right on that cutoff line may not have had much of a problem with social jetlag affecting their health.”
For example, a participant who had 1.6 hours difference in sleep pattern may not be the same as those who had a disruption of four hours.
“It could be that those 90-minute people have very little impact and the numbers were being skewed by the people way out in the tail with more than three hours,” Lakin-Thomas said.
Shift workers need to pay special attention
Despite her criticisms, she said, studies have shown that social jet lag can impact one’s health in terms of weight gain, digestive problems and an increase in risks for diseases like diabetes and cancer.
The researchers of The European Journal of Nutrition study point to several other papers linking sleep disturbances with impaired health. For example, a 2016 study published in the BMJ found that shift workers may be more at risk of cardiovascular disease, Type 2 diabetes and cancer.
A 2017 study published in Sage Journals found an association between social jetlag and a higher prevalence of diabetes.
More recently, a 2022 research review in the Journal of Clinical Sleep Medicine linked shift work to higher risks for serious health problems, such as heart attack and diabetes.
“Shift workers need to pay special attention to supporting their health with such big changes in sleep patterns. There is a lot of interest in understanding how to best support shift workers and it’s sure to be an area with increased research,” Bermingham wrote.
“The data does suggest that the shift in sleep alone is having an impact but more studies to understand the details on other factors are needed to confirm the causal pathways.”