People whose underlying biological clock does not match the sleep hours imposed by modern work schedules have metabolic risk factors that may predispose them to a higher risk for type 2 diabetes and heart disease, according to a new study published online November 18 in the Journal of Clinical Endocrinology and Metabolism.
The work is the first to link so-called "social jet lag" with increased metabolic risk in middle-aged adults. Social jet lag refers to the disconnect between a person's natural circadian rhythm and the restrictions placed on it by social and work obligations.
"Our results, 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," commented first author Patricia Wong, MS, a predoctoral student at the University of Pittsburgh, Pennsylvania.
"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," she added.
"It's been shown that regulating sleep times can help treat insomnia, and this emerging evidence along with other [work] suggests that perhaps doing so will have benefits in treatment and prevention of other diseases," she said.
Does Day-to-day Circadian Dysregulation Have an Impact?
Past research, including some conducted in shift workers, has indicated that extreme disturbances in the circadian rhythm can increase the risk for many diseases, including type 2 diabetes, obesity, and cardiovascular disease.
But so far, other types of sleep problems experienced more routinely as part of modern work schedules have received less attention.
For the current analysis, participants were recruited from a larger study called Adult Health and Behavior Project Phase 2 (AHAB-II), which is looking at psychosocial, behavioral, and vascular risk factors for preclinical vascular disease. Enrollment occurred between March 2008 and October 2011.
The study included 447 healthy adults who worked full- or part-time normal day shifts (53% female; 83% white; mean age, 42.7 years). Participants received up to $410 for taking part and were excluded if they had a history of schizophrenia, bipolar disorder, heavy alcohol consumption, less than eighth-grade reading level or were pregnant and/or had several medical illnesses that could affect sleep.
They wore a device (Actiwatch-16, Philips Electronics) that monitored their movements and could measure time spent sleeping, from which the researchers evaluated social jet lag, defined as the difference in minutes between the halfway point in their sleep cycle on workdays compared with free days.
This use of a device to quantify participants' sleep times, rather than relying on self-report, is a strength of the study, note Ms Wong and colleagues
They also used a validated scale to assess circadian chronotype, or naturally occurring variations in a person's preferred bedtime and times of peak alertness (ie, whether they were an owl [evening chronotype] or a lark [morning chronotype]). And they measured sleep and diet quality, physical activity, and depressive symptoms using self-reported validated questionnaires.
Can We Treat Social Jet Lag? More Studies Needed
Results showed that 84.8% of participants had later halfway points in their sleep cycles on free days compared with workdays. In contrast, 15.2% of participants had earlier halfway points on free days compared with workdays.
People who experienced social jet lag woke up earlier and slept less on workdays and woke up later and slept longer on free days (P < .05).
Having social jet lag was linked to lower HDL, higher triglycerides, higher fasting plasma insulin, insulin resistance, greater body mass index (BMI), and larger waist circumference. These associations remained even after researchers controlled for sleep quality and other sleep measurements, depressive symptoms, and health behaviors like physical activity, calorie intake, and alcohol consumption (P < .05).
People with evening chronotypes also had higher triglycerides and lower HDL levels, after researchers controlled for sleep characteristics and demographics (P < .05).
However, in the current sample, only 4.9% of participants met a conventional threshold for evening chronotype, as the researchers explain that "eveningness" tends to peak at around age 20, and individuals progressively demonstrate increasing "morningness" during midlife.
Evening chronotypes are more likely to experience social jet lag compared with morning types, and this may explain why the mean time of social jet lag was only 44 minutes in the current sample, the researchers say.
Nevertheless, "our results show that a mismatch in sleep timing between workdays and free days was linked to greater cardiometabolic risk, specifically with components of glycemic control, serum lipids, and adiposity," they note.
"To our knowledge, this is the first study to show social jet lag associated with numerous metabolic risk factors in community-dwelling, midlife adults, independently of poor sleep characteristics and health behaviors," they add.
Further research is needed, however, Ms Wong pointed out.
If the findings are confirmed, "then as a society we need to think strongly about how our modern-day work and social obligations are affecting us," she noted, adding that it will also be important to evaluate whether treating social jet lag somehow can help decrease associated health risks.
The authors report no relevant financial relationships.
J Clin Endocrinol Metab. Published online November 18 2015. Abstract
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Cite this: 'Social Jet Lag' Affects Risk of Type 2 Diabetes, Heart Disease - Medscape - Nov 19, 2015.