The negative health effects of shift work have been widely reported.
Working and sleeping during hours that are misaligned with the body’s circadian rhythm have been linked to poor sleep, decreased alertness, inflammation and high blood pressure.
In the long-term, shift work is associated with higher risks of metabolic syndrome, heart disease, Type 2 diabetes, obesity, certain cancers and cognitive impairment.
Circadian rhythms, set by the body’s master internal clock, regulate our sleep-wake cycle, digestion, nutrient metabolism, body temperature and other bodily processes. Circadian rhythms make sure these processes are optimized at various times during a 24-hour period.
Now, new study findings add to emerging evidence that sleep disruptions much smaller than those associated with shift work – social jetlag – may also have health consequences.
What is social jetlag?
Social jetlag results from having different weekday and weekend (work-free days) sleep schedules.
It occurs when school, work and/or social obligations put us out of sync with our circadian sleep-wake cycle. On weekdays we might get up early ahead of our natural wake time and on weekends we might stay up late past our natural bedtime.
Sleep scientists define social jetlag as a difference of one hour or more between your mid-point sleep on work versus work-free days. (Mid-point sleep is the time halfway between when you go to bed and when you wake up.)
Past research has identified strong connections between social jetlag and sleep deprivation, mental fatigue, increased heart rate, weight gain, insulin resistance, reduced HDL (good) cholesterol, elevated blood triglycerides (fats), depression and poor diet.
The latest research
For the study, published this month in the European Journal of Nutrition, researchers from King’s College London examined the relationship between social jetlag and diet quality, diet habits, inflammation and gut microbiome composition.
Our gut microbiome, the active community of trillions of microbes that live inside our large intestine, is thought to influence our mood, mental health and appetite, as well as the risk for chronic diseases including inflammatory bowel disease, Type 2 diabetes, cardiovascular disease and obesity.
Study participants included 934 healthy individuals, ages 18 to 65, from ZOE PREDICT 1, a large-scale nutrition study designed to quantify and predict individual metabolic responses to different foods.
Participants completed diet and sleep questionnaires and provided blood and stool samples. Social jetlag was defined as a difference of 1.5 hours or more in mid-point sleep between weekday (Sunday-Thursday) and weekend (Friday-Saturday) nights.
Most participants (82 per cent) got, on average, seven to nine hours of sleep each night. Sixteen per cent of participants were affected by social jetlag.
People with social jetlag had differences in the makeup of their gut microbiome.
Furthermore, three of the six microbial species that were more abundant in the social jetlag group have previously been tied to cardiovascular risk and inflammation.
Some, but not all, of these microbiome differences were linked to dietary factors.
Compared with people who had a consistent a sleep-wake schedule across the week, those with social jetlag had an overall poor diet, a higher intake of sugar-sweetened beverages, and a lower intake of whole fruit and nuts, all of which can directly influence the gut microbiome.
These differences in diet quality are in line with previous findings that people with social jetlag consume more calorie-dense foods and less fibre, fruit and vegetables.
Social jetlag may influence dietary choices by disrupting appetite regulation. Circadian misalignment has been shown to increase the release of ghrelin, a hormone the stimulates appetite and signals the brain it’s time to eat.
These new findings raise the possibility that even a small mismatch between our sleep-wake timing and the body’s circadian timing may have unfavourable effects on the gut microbiome.
They also hint that eating a microbiome-friendly diet rich in whole plant foods could prevent some of the variation in gut microbes that was observed with social jetlag.
Whole grains, vegetables, fruits, nuts, seeds and pulses (e.g., chickpeas, black beans, lentils) contain fermentable fibres which are digested by some gut bacteria. In the process, short chain fatty acids are produced, compounds which help regulate immune function, dampen inflammation and strengthen the intestinal barrier.
Probiotic-containing fermented foods, such as kefir, kimchi and kombucha are also thought to contribute to a healthy microbiome.
Maintaining a consistent sleep-wake schedule (and getting sufficient sleep) and eating a healthy diet are lifestyle habits that have the potential to influence your microbiome – and your long-term health – for the better.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD.