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 Lack of sleep has long been linked to a wide range of so-called
metabolic abnormalities, including obesity, high blood pressure,
high cholesterol, and diabetes. But much of this research focused on
the effect of the average amount of sleep people get, and not on how
much sleep routines varied from one day to the next, said study
coauthor Tianyi Huang, of Brigham and Women's Hospital and Harvard
Medical School in Boston.
"In this study, we showed that high night-to-night differences in
sleep schedules (either duration or timing) are associated with
higher risk of developing metabolic problems, particularly multiple
metabolic abnormalities at the same time," Huang said by email.
"Importantly, this finding is independent of sleep duration/quality,
that is, more irregular sleep schedules are associated with higher
metabolic disease risk no matter one has short or long sleep
duration or has good or poor sleep quality," Huang added. "The
negative impact of short sleep duration on some nights cannot be
compensated for by extended longer sleep duration on other nights,"
Huang said by email.
As reported in Diabetes Care, the researchers had 2,003 patients do
home-based sleep studies for one week using devices known as
actigraphs, which assess nighttime movements and sleep-wake cycles.
On average, these people got about 7.15 hours of sleep each night
and went to bed at around 11:40 p.m. Roughly two-thirds of them had
more than one hour of variation in sleep duration, and 45% of them
had more than one hour of variation in their bedtime.
A total of 707 participants, or 35%, had so-called metabolic
syndrome, or multiple types of metabolic abnormalities that increase
the risk for heart disease, including increased blood pressure, high
blood sugar, excess body fat around the waist, and abnormal
cholesterol or triglyceride levels.
Compared to people who had less than one hour of variation in sleep
duration, people whose sleep duration varied by 60 to 90 minutes
were 27% more likely to have metabolic syndrome. The increased risk
rose to 41% for people with 90 to 120 minutes of variation in sleep
duration, and jumped to 57% with more than two hours of variation in
sleep duration.
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Compared with people with no more than a half hour of variation in
their nightly bedtime, people whose bedtime varied by 30 to 60
minutes had a similar risk for metabolic syndrome. But the risk was
14% higher when bedtimes varied by 60 to 90 minutes and 58% higher
when bedtimes varied by more than 90 minutes.
The study wasn't a controlled experiment designed to prove whether
or how shifts in sleep duration or bedtimes might directly cause
metabolic syndrome.
"The reason increased variability has a detrimental effect on
metabolic heath may have to do with our biological clocks," said
Kristen Knutson, a researcher at Northwestern University Feinberg
School of Medicine in Chicago who wasn't involved in the study.
"We have internal 24-hour rhythms of many processes that impact
metabolism and for optimal function these rhythms should be
synchronized with each other and with the environment," Knutson said
by email. "If we are sleeping at different times and different
amounts, our internal clocks may have difficulty staying
synchronized, which may impair function."
One limitation of the analysis is that researchers only assessed
sleep during that one week, and it's possible the week-long sleep
study didn't reflect sleep patterns over longer periods of time.
Researchers also lacked data on several factors that can impact
sleep regularity like breakfast consumption and meal timing, both of
which can also impact metabolic health.
Most adults need at least 7 hours of sleep a night, according to the
U.S. Centers for Disease Control and Prevention.
To get the ideal amount of sleep and avoid nighttime awakening and
sleep disturbances that make people wake up feeling unrested, the
CDC recommends setting a consistent bedtime, sleeping in a dark room
without any electronics around, and avoiding large meals, caffeine,
and alcohol before bedtime. (http://bit.ly/2xrHFTC)
SOURCE: http://bit.ly/2xpEtYH Diabetes Care, online June 5, 2019.
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