(RxWiki News) It's not just how much sleep you get that plays a part in your health - it's also when you sleep. An out-of-whack biological clock can mean poor health and higher risk of disease.
A new study reveals that insufficient sleep, and sleeping during shifting time periods that upsets a person's internal clock, can increase a person's risk of obesity and diabetes.
All people have an internal clock called their circadian cycle which helps regulate when it's time for them to sleep, eat and wake up.
Messing with the gears of this sleep clock can have serious health consequences.
"Get sufficient, consistent sleep every night at the same time."
Orfeu Buxton, PhD, a neuroscientist with the Division of Sleep Medicine at Brigham and Women's Hospital in Boston, led a controlled experiment to find out the physical effects of altering people's sleeping times and patterns.
Buxton's team recruited 21 healthy individuals to be a part of the study in a controlled environment for almost six weeks.
The research team controlled when and for how long the individuals slept and what their diet and daily activities included.
Initially, all the participants were given a 10-hour window for sleep each night for approximately a week.
Then, for three weeks, they were restricted to 5.6 hours of sleep per 24-hour period, but this block of sleep was moved to various times of day and night, just as a typical shift worker's sleep might move around from one week to the next.
Their sleep period was shifted by at least a few hours every day, intentionally disrupting their circadian clocks.
At the end of the study, participants spent nine days with recovery sleep during normal nighttime hours.
The data from the study revealed that the shifting schedule of lesser amounts of sleep decreased the individuals' resting metabolic rate.
During the three weeks of inconsistent, restricted sleep, the participants' blood sugar levels increased after eating as well because their pancreas was not producing adequate insulin to control their glucose levels.
During the three weeks of poor sleep, the participants also had slightly elevated levels of cortisol, a stress hormone that helps the body maintain blood sugar levels, blood pressure and immune system functions.
However, too much cortisol prevents the body from relaxing so that it can conduct normal physical activities at an appropriate rate.
"We think these results support the findings from studies showing that, in people with a pre-diabetic condition, shift workers who stay awake at night are much more likely to progress to full-on diabetes than day workers," Buxton said.
"Since night workers often have a hard time sleeping during the day, they can face both circadian disruption working at night and insufficient sleep during the day," he said. "The evidence is clear that getting enough sleep is important for health, and that sleep should be at night for best effect."
William Kohler, MD, director of the Florida Sleep Institute in Spring Hill, Florida, said this study supports past studies in providing evidence of the negative effects of poor quality or poor quantity of sleep. However, what can be learned form this study is limited by its design, he said.
"What's hard is to tell if it's from the circadian change or the insufficient sleep," Dr. Kohler said. Because the study altered the sleeping times (shift changes) and restricted sleep, he said it's not possible to separate the effects of each of these different changes.
Dr. Kohler also pointed out the small number of participants studied and the short amount of time for the study compared to other sleep studies. Also, the participants were provided with 10 hours to sleep initially, but the study does not state how much actual sleep each participant got in the beginning weeks.
The study appeared April 11 online in the journal Science Translational Medicine. Buxton has been a consultant and expert witness for an attorney in a case concerning sleep, circadian rhythms and diabetes in railroad workers.
Another author, Charles Czeisler, has several financial connections to pharmaceutical companies and has served as a consultant for a long list of medical and other companies.
The research was funded by the National Institute on Aging; National Heart, Lung and Blood Institute; National Center for Research Resources; Center for Clinical Investigation of the Harvard Clinical and Translational Science Center; Joslin Diabetes and Endocrinology Research Center Service Specialized Assay Core; the National Space Biomedical Research Institute; and Natural Sciences and Engineering Research Council of Canada.