A 14-day UK study shows that differences between daytime and weekend sleep hours may be linked to when people use up energy, with the clearest pattern occurring later in the evening.
Study: Social jetlag predicts greater evening energy intake in a UK cohort. Image credit: PawelKacperek / Shutterstock
In a recent study published in the journal npj Biological timing and sleepa group of researchers examined whether social jetlag is associated with the timing of daily energy intake during weekdays and weekends among healthy adults in the United Kingdom.
Background
Nearly half of the general population may experience more than an hour of social jetlag, a mismatch between biological sleep time and socially required schedules. Social jetlag has been associated with obesity, metabolic syndrome, cardiometabolic risk factors, and dietary behaviors. Circadian rhythms regulate various biological processes, including metabolism and responses to food. People with evening clocks usually accumulate more sleep debt during the week which can affect their eating behavior. However, most studies of social jetlag and eating behavior are cross-sectional, and further longitudinal research is needed to clarify whether social jetlag is associated with differences in energy intake patterns or diet quality.
About the Study
Researchers conducted a 14-day longitudinal observational study involving 101 healthy adults living in the UK. The study included men and women and covered two consecutive work weeks and two weekends to capture differences in eating patterns on different days. Each participant was expected to record all food and beverages consumed throughout the study. In addition, self-reported height, weight, physical activity, smoking status, alcohol consumption, employment, and household characteristics were collected. body mass index (BMI) was calculated from self-reported height and weight, and chronotype was assessed using the mean sleep point on free days corrected for sleep debt (MSFsc).
Social jetlag was calculated from the differences in sleep time between work days and days off. Subjects were divided into groups based on whether their social jetlag was less than 1 hour or more than 1 hour. Social jetlag was also studied as a continuous factor. Statistical analyzes used Poisson Pseudo-Maximum Likelihood (PPML) regression models to assess associations between social jetlag and energy intake at different times of day. Models incorporated sex, time of day, time of day, and related interactions and adjusted for age, BMI, smoking status, alcohol consumption, workplace location, and dependent children at home.
Study Results
In this study, researchers looked at 101 healthy adults, with 77.5% women and 22.5% men. The average age of the participants was about 32.7 years, while the average social jetlag was about 53 minutes. Across the cohort, energy intake followed a consistent diurnal pattern, increasing from early morning to a peak between 4:00 p.m. and 8:00 p.m., and then decreased later at night. Men showed a greater peak in energy intake, particularly in the early evening, than women. Level of social jetlag was associated with differences in energy intake time, with patterns varying by gender and day type.
When the women in the two social jetlag groups were compared, those with less than an hour of social jetlag tended to distribute their energy earlier in the day. Among women, lower social jetlag was associated with greater energy intake in the early morning hours of the day. Women with more than an hour of social jetlag, in contrast, consumed more energy late at night. On the weekend, women with less social jetlag consumed more energy in the late morning than those with more social jetlag. Overall, the results indicate that greater social jetlag was associated with a later distribution of energy intake in this cohort. analyzes did not show whether total daily energy intake differed between groups.
The smaller male subgroup showed evidence of a similar pattern, especially on weekends. The largest weekend difference was seen when men with less than an hour of social jetlag had higher energy intake in the early morning, although this difference did not reach conventional statistical significance and significantly higher intake in the early afternoon. The difference in the early afternoon was 266 kcal. Overall, the findings suggest that temporal patterns of energy intake differed between women and men, although the small sample of men limits certainty about these patterns.
When social jetlag was analyzed as a continuous measure instead of categorical groups, the overall findings showed generally similar temporal patterns, although several estimates were not statistically significant. In women, model estimates generally indicated that each additional hour of social jetlag was associated with lower energy intake earlier in the day and higher energy intake later in the evening. The statistically significant finding of the week was a 62.5 kcal increase in late-night energy intake per additional hour of social jetlag, with a 95% confidence interval.CI) from 5.3 to 119.7 kcal and a p value of 0.032.
Weekend analyzes showed an even stronger trend toward reduced morning intake with increasing social jetlag. In men, weekday associations differed somewhat from those seen in women, with weekends showing reduced evening energy intake with increased social jetlag. Each additional hour of social jetlag was associated with 128.5 kcal higher weekday morning intake in men, with 95% CI 7.9 to 249.0 kcal and p value 0.037, and 147.3 kcal lower weekend intake, with 95% CI −29 to 29 kcal. p-value 0.018.
Sensitivity analyzes using categories of low, moderate, and high social jetlag provided additional support for the late-night female pattern, although male patterns were less consistent due to small group sizes. Participants with the highest levels of social jetlag were primarily responsible for the greater late-night energy intake observed among women. Removing chronotype from the statistical models did not substantially change the results, although the cohort had limited variation in chronotype.
Conclusion
The findings showed that social jetlag was associated with changes in the timing of daily energy intake. Analyzes did not show whether total daily energy intake differed between groups. People with higher levels of social jetlag tended to consume more energy late at night, while people with lower levels of social jetlag tended to consume food earlier in the day.
These patterns differed somewhat between women and men, but remained broadly similar in supplementary statistical analyses, although the small subgroup of men warrants caution. Although the observed effects were modest and unlikely to fully explain the previously reported links between social jetlag and obesity or metabolic disease, the results highlight the importance of considering meal timing alongside sleep schedules when assessing metabolic health. However, the small, predominantly female, highly active sample and self-reported dietary data limit generalizability to the wider United Kingdom population.
