People who tend to indulge in weekend lie-ins may develop potentially harmful alterations in their gut microbiome, putting them at risk of disease, according to a study in the European Journal of Nutrition.
Researchers from King's College London said they had conducted the first investigation to identify multiple associations between 'social jetlag' and diet quality, diet habits, inflammation, and gut microbial composition within a single cohort.
The study was based on 934 participants aged 18 to 65 from the ZOE PREDICT cohort, an intervention study of diet–microbiome–cardiometabolic interactions. The data was used to assess self-reported habitual sleep patterns, gut microbial composition, diet, and cardiometabolic health.
Researchers particularly looked for a difference of ≥ 1.5 hours in the mid-sleep time point (the halfway point between sleep time and wake-up time) between weekdays and weekends. This indicated whether there was a pattern of sleep and wake times adjusted to workdays, with a shift in sleeping times on work-free days. This habit of social jetlag (SJL) — "a parameter of circadian misalignment" — is more prevalent in individuals with late chronotypes (those who are biologically programmed for later bedtimes and wake times), they explained.
The investigation found that 145 (16%) of the participants had SJL and, compared with the no-SJL group, were more likely to be male (39% vs 25%), younger (38.4 ± 11.3y vs 46.8 ± 11.7y), and to have an average sleep duration of less than 7 hours (5% vs 3%).
The proportion with SLJ and the average sleeping time differed from those found in other cohorts, possibly related to the demographic composition of the participants, the researchers said.
'Social Jetlag' Associated with Poor Diet and Microbiome Changes
In the study, SJL was associated with lower overall diet quality, including higher intakes of potatoes and sugar-sweetened beverages, and lower intakes of fruits and nuts – factors that may directly influence the abundance of specific microbiota. In addition, the SJL group had slightly higher markers of inflammation. However, these differences were small and rendered non-significant after testing adjustments.
Blood, stool, and gut microbiome samples showed that 17 bacterial species were significantly different between the groups. Nine species had greater abundances in people with SJL and eight were greater in those without SJL, with some of these differences mediated in part by diet.
The changes in gut microbiota composition in participants with SJL was suggestive of intestinal dysbiosis, which has been associated with poor diet quality, obesity, inflammation, metabolic syndrome, and cardiovascular risk.
The team commented that "a bidirectional relationship exists between sleep quality and the composition of the gut microbiome", and that previous research had linked sleep disturbances with impaired health. In particular, shift work has been associated with an increased risk of cardiovascular disease, weight gain, increased BMI, and metabolic disturbances, including diabetes.
Weekday – Weekend Sleep Differences Could Affect Health
There was less awareness, the team said, that biological rhythms can be affected by smaller inconsistencies in sleeping patterns, such as waking early with an alarm clock on workdays, compared with waking naturally on non-workdays.
"Emerging evidence suggests, beyond large circadian shifts in sleeping patterns such as shift work, smaller irregularities such as social jetlag may be enough to affect health outcomes," the researchers commented.
Senior author Dr Wendy Hall PhD, a reader in nutritional sciences at King’s College London said: "We know that major disruptions in sleep, such as shift work, can have a profound impact on your health. 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.
"Some of these associations were linked to dietary differences, but our data also indicates that other, as yet unknown, factors may be involved. We need intervention trials to find out whether improving sleep time consistency can lead to beneficial changes in the gut microbiome and related health outcomes."
Sleep "A Key Pillar of Health"
The researchers said that SJL has been estimated to affect more than 40% of the general population, and previous research has shown it to be associated with weight gain, chronic illness, and mental fatigue. In addition, sleep disturbances can affect inflammatory markers and increase oxidative stress, which was a potential mechanism behind increased incidence of cardiovascular disease associated with sleep deprivation.
Circadian misalignment may cause adverse changes in cardiovascular risk factors both directly and indirectly through diet, as well as associations between SJL and poor diet, adiposity, and metabolic disturbances, including glycaemic dysregulation, lower high-density lipoprotein, and higher triglycerides, insulin, insulin resistance, adiposity, and metabolic syndrome.
First author Kate Bermingham, PhD, a research associate at King’s College London, and senior nutrition scientist at ZOE, said: "Sleep is a key pillar of health, and this research is particularly timely given the growing interest in circadian rhythms and the gut microbiome. Even a 90-minute difference in the mid-point of sleep can encourage microbiota species which have unfavourable associations with your health.”
The researchers concluded that their findings "raise the possibility that socially-imposed chronic circadian rhythm disturbance caused by sleep–wake shifts could influence the human gut microbiota". They suggested that this could "guide possible microbial therapies for clinical intervention in sleep-related diseases, such as obesity, diabetes, cardiovascular disorders, and cognitive impairments".
The research was funded by ZOE Ltd, Wellcome Trust, the Medical Research Council, Versus Arthritis, European Horizon 2020, Chronic Disease Research Foundation, and the National Institute for Health Research.