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‘Social jetlag’ resulting from irregular sleep patterns associated with harmful gut bacteria

Irregular sleep patterns, caused by ‘social jetlag’ – the shift in a person’s internal body clock when sleeping patterns change between workdays and free days – are associated with harmful gut bacteria and adverse health outcomes, according to a new study.

Undertaken by King’s College London (KCL) and published in the European Journal of Nutrition, the study was designed to explore the relationship between social jetlag and gut microbial composition, diet and cardiometabolic health.

It found that social jetlag is associated with unfavourable diet quality, including a higher intake of potatoes and sugar-sweetened beverages and lower intakes of fruits and nuts, together with slightly higher markers of inflammation, compared to those without social jetlag.

The researchers used information from the ZOE PREDICT 1 study, which includes data from 1,002 monozygotic, dizygotic and non-twin healthy UK individuals aged 18-65 years.

The team assessed demographic, diet, cardiometabolic, stool metagenomics and postprandial metabolic measures. Sleep patterns were self-reported and used to calculate social jetlag. This was deemed to be a 90-minute difference in the timing of the midpoint of sleep – the halfway point between when a person goes to sleep and when they wake up – on weekdays versus weekend days.

The team also collected blood samples following the consumption of a standardised meal consisting of two high-fat muffins and a milkshake.

Social jetlag and the gut microbiome

A total of 934 individuals were included in the analysis and 145 were defined as having social jetlag and the others had a routine sleep schedule. All participants were healthy and lean, and slept for over seven hours a night throughout the week.

In an analysis of their gut microbiomes, three out of six microbiota species linked to ‘unfavourable’ health outcomes were more abundant in the social jet lag group. These microbes are associated with poor diet quality and are indicators of obesity and cardiometabolic health, and create markers in the blood related to higher levels of inflammation.

Senior author for the study Wendy Hall, 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 seems 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.‘

The gut microbiome refers to the community of bacterial species within the intestines and plays an important role in the overall health of the host. In fact, the microbiome can be easily disturbed, for instance after taking antibiotics, although taking a probiotic yogurt appears to restore the antibiotic-induced disturbance.