By Jeff Minerd. This article was published 18 November 2015 on Medpage Today.
People who are early to bed and early to rise during the work week but like to stay up late and sleep in on the weekends may be increasing their cardiometabolic risk, researchers said.
The difference between one’s naturally-preferred and socially-imposed sleep schedules — termed “social jetlag” — was associated with poorer lipid profiles, worse glycemic control, and increased adiposity in healthy adults, reported a research team led by Patricia Wong, a PhD candidate at the University of Pittsburgh, in the Journal of Clinical Endocrinology & Metabolism.
“If future studies replicate what we found here, then we may need to consider as a society how modern work and social obligations are affecting our sleep and health,” Wong said. “There could be benefits to clinical interventions focused on circadian disturbances, workplace education to help employees and their families make informed decisions about structuring their schedules, and policies to encourage employers to consider these issues.”
The study included 447 healthy adults ages 30-54 who worked either part- or full-time day shifts. They were 53% female and 83% white. Participants wore an actigraph wristband that measured their movement and sleep 24 hours a day for 7 days. The researchers collected blood samples for laboratory tests and assessed participants’ diet and exercise habits via questionnaire.
Wong and colleagues compared participants’ sleep schedules on their days off work, assumed to be their naturally-preferred circadian sleep cycle, with their sleep schedules on workdays. The difference between the midpoint of the two sleep schedules, measured in minutes, was defined as social jetlag. The investigators looked for associations between social jetlag and cardiometabolic risk factors.
A total of 111 study participants had a social jetlag of more than 60 minutes. Compared to the other study participants, these individuals had:
- Higher mean triglycerides: 107 mg/dL versus 91 mg/dL (P=0.009)
- Lower mean HDL-cholesterol: 54 mg/dL versus 57 mg/dL (P=0.014)
- Higher mean fasting insulin levels: 13.5 µU/mL versus 12 µU/mL (P=0.03)
- More insulin resistance as measured by homeostatic model assessment: 4.0 versus 3.7 (P=0.028)
- Greater mean waist circumference: 94 cm versus 89 cm (P=0.001)
- Higher mean BMI: 28 versus 26 (P=0.004)
All study participants had some degree of social jetlag. The majority (85%) stayed up later and slept in on their days off. A minority (15%) went to bed and woke earlier on their days off.
Those who stayed up later and slept in on their days off had a greater degree of social jetlag, Wong and colleagues noted. “The relatively later awakening time on free days may be perpetuating a cycle of circadian misalignment because it delays circadian timing, thus interfering with entrainment to workday schedules,” they wrote.
As far as potential biological mechanism to explain their findings, Wong and colleagues noted research has shown that fat accumulation in adipose tissue, insulin secretion in the pancreas and liver, and food absorption in the intestine are all affected by circadian rhythms.
“Our results in this study, in conjunction with recent research conducted throughout other countries, suggest that even healthy, nonclinical populations may be experiencing important, regular shifts in their sleep cycle that is unfortunately working ‘against’ their biological clock,” Wong told MedPage Today via email.
“Based on our findings and existing literature on social jet lag as well as circadian sleep disorders, clinicians may want to pay attention to any irregularity in sleep schedules and discrepancy between when people are sleeping compared to what their natural preference is,” Wong said. “It’s been shown that regulating sleep times can help treat insomnia, and this emerging evidence along with others suggest that perhaps doing so will have benefits in treatment and prevention of other diseases.”