Irregular sleep patterns linked to metabolic disorders

Obesity, diabetes, high cholesterol more prevalent among irregular sleepers

June 5, 2019

Science Daily/NIH/National Heart, Lung and Blood Institute

A new study has found that not sticking to a regular bedtime and wakeup schedule -- and getting different amounts of sleep each night -- can put a person at higher risk for obesity, high cholesterol, hypertension, high blood sugar and other metabolic disorders. In fact, for every hour of variability in time to bed and time asleep, a person may have up to a 27% greater chance of experiencing a metabolic abnormality.

The results of the study, which was funded by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health, appear today in the journal Diabetes Care.

"Many previous studies have shown the link between insufficient sleep and higher risk of obesity, diabetes, and other metabolic disorders," said study author Tianyi Huang, Sc.D., epidemiologist of the Channing Division of Network Medicine at Brigham and Women's Hospital, Boston. "But we didn't know much about the impact of irregular sleep, high day-to-day variability in sleep duration and timing. Our research shows that, even after considering the amount of sleep a person gets and other lifestyle factors, every one-hour night-to-night difference in the time to bed or the duration of a night's sleep multiplies the adverse metabolic effect."

For the current study, researchers followed 2,003 men and women, ages 45 to 84, participating in the NHLBI-funded Multi-Ethnic Study of Atherosclerosis (MESA). The participants were studied for a median of six years to find out the associations between sleep regularity and metabolic abnormalities. To ensure objective measurement of sleep duration and quality, participants wore actigraph wrist watches to closely track sleep schedules for seven consecutive days. They also kept a sleep diary and responded to standard questionnaires about sleep habits and other lifestyle and health factors. Participants completed the actigraphy tracking between 2010 and 2013 and were followed until 2016 and 2017.

"Objective metrics and a big and diverse sample size are strengths of this study," said Michael Twery, Ph.D., director of the NHLBI's National Center on Sleep Disorders Research. "As is the study's ability to look not only at current factors, but to conduct a prospective analysis that allowed us to assess whether patterns of irregular sleep could be linked to future metabolic abnormalities."

The researchers' hypothesis that there were, in fact, such associations, proved correct. Individuals with greater variations in their bedtimes and in the hours they slept had a higher prevalence of metabolic problems, and these associations persisted after adjusting for average sleep duration. This was also the case when they looked at the participants who developed metabolic disorders during the 6.3 years of follow up.

The prospective results showed that the variations in sleep duration and bedtimes preceded the development of metabolic dysfunction. According to the authors, this provides some evidence supporting a causal link between irregular sleep and metabolic dysfunction.

Participants whose sleep duration varied more than one hour were more likely to be African-Americans, work non-day shift schedules, smoke, and have shorter sleep duration. They also had higher depressive symptoms, total caloric intake, and index of sleep apnea.

Increasing sleep duration or bedtime variability was strongly associated with multiple metabolic and simultaneous problems such as lower HDL cholesterol and higher waist circumference, blood pressure, total triglycerides, and fasting glucose.

"Our results suggest that maintaining a regular sleep schedule has beneficial metabolic effects," said study coauthor Susan Redline, M.D., senior physician in the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital. "This message may enrich current prevention strategies for metabolic disease that primarily focus on promoting sufficient sleep and other healthy lifestyles."

https://www.sciencedaily.com/releases/2019/06/190605133514.htm

Study links irregular sleep schedules to adverse metabolic health in women

Study is first to examine individual differences in habitual sleep timing in relation to indices of metabolic health

February 1, 2016

Science Daily/American Academy of Sleep Medicine

Frequent shifts in sleep timing may be related to adverse metabolic health among non-shift working, midlife women, new research shows. Results show that greater variability in bedtime and greater bedtime delay were associated with higher insulin resistance, and greater bedtime advance was associated with higher body mass index (BMI).

Results show that greater variability in bedtime and greater bedtime delay were associated with higher insulin resistance, and greater bedtime advance was associated with higher body mass index (BMI). In prospective analyses, greater bedtime delay -- for example, staying up 2 hours later than usual -- also predicted an increase in insulin resistance 5 years later. The cross-sectional and prospective associations between these measures were significant only when both weekdays and weekends were included in the analysis, suggesting that large deviations in bedtime between work days and free days contributed to impaired glucose regulation.

"Irregular sleep schedules, including highly variable bedtimes and staying up much later than usual, are associated in midlife women with insulin resistance, which is an important indicator of metabolic health, including diabetes risk," said senior author Martica Hall, PhD, professor of psychiatry at the University of Pittsburgh. "We found that weekday-weekend differences in bedtime were especially important."

Study results are published in the February issue of the journal Sleep.

"This study emphasizes the important health benefits of keeping a regular sleep schedule," said American Academy of Sleep Medicine President Dr. Nathaniel Watson, who was not involved in the study. "In addition to sleeping 7 or more hours per night on a regular basis, adults should strive to maintain a consistent schedule by going to bed and waking up at the same times on weekdays and weekends."

Led by Hall and lead author Briana J. Taylor, the research team analyzed data from the SWAN Sleep Study, an ancillary project to the Study of Women's Health Across the Nation (SWAN). The community-based sample comprised 370 Caucasian, African American and Chinese non-shift working women between the ages of 48 and 58 years. Daily diary-reported bedtimes were used to calculate four measures of sleep timing: mean bedtime, bedtime variability, bedtime delay and bedtime advance. BMI and insulin resistance were measured at baseline and again an average of 5 years later.

"The results are important because diabetes risk increases in midlife women," said Hall. "Our study suggests that irregular sleep schedules may be an important piece of this puzzle. The good news is that sleep timing is a modifiable behavior. Metabolic health was better in women who had more regular sleep schedules, including regular bedtimes across weekdays and weekends."

According to the authors, irregular bedtime schedules expose the body to varying levels of light, which is the most important timing cue for the body's circadian clock. By disrupting circadian timing, bedtime variability may impair glucose metabolism and energy homeostasis.

The authors suggest that future studies of sleep timing and metabolic health should examine potential mechanisms including melatonin as well as other hormones that are relevant to metabolic health and sensitive to circadian misalignment, including leptin, ghrelin and cortisol.

http://www.sciencedaily.com/releases/2016/02/160201125510.htm