12 April 2012

Sleep Patterns Inconsistent With Biological Clock May Lead to Diabetes and Obesity

The human biological clock is an internal mechanism that "schedules" regular body activities based on a 24 hour period.

Known as a circadiam rhythm, it covers any biological process which displays an endogenous, entrainable oscillation of one day or about 24 hours. The bio-clock is have been widely observed in living organisms like plants, animals and even in fungi and certain bacterium.

The circadiam rhythms are built in the body but can be adjusted to the local environment, the most common and most important being daylight.

Common processes influenced by the circadian rhythm are hunger, bowel movement, and sleeping and waking hours. For a process to be considered to be circadian, it should be repeated once every 24 hours, it should not be influenced by external factors (endogenous), the process is aligned to a schedule (entrainable), and that the process still holds true despite changing temperature conditions.

Disrupted sleep patterns that are inconsistent with the body's 'internal biological clock' may lead to diabetes and obesity

A study by researchers at Brigham and Women's Hospital (BWH) reinforces the finding that too little sleep or sleep patterns that are inconsistent with our body's "internal biological clock" may lead to increased risk of diabetes and obesity. This finding has been seen in short-term lab studies and when observing human subjects via epidemiological studies. However, unlike epidemiological studies, this new study provides support by examining humans in a controlled lab environment over a prolonged period, and altering the timing of sleep, mimicking shift work or recurrent jet lag.

The study is electronically published in Science Translational Medicine.

Video: Circadiam Rhythm and Sleep

Researchers hosted 21 healthy participants in a completely controlled environment for nearly six weeks. The researchers controlled how many hours of sleep participants got, as well as when they slept, and other factors such as activities and diet. Participants started with getting optimal sleep (approximately 10 hours per night). This was followed by three weeks of 5.6 hours of sleep per 24-hour period and with sleep occurring at all times of day and night, thereby simulating the schedule of rotating shift workers. Thus, during this period, there were many days when participants were trying to sleep at unusual times within their internal circadian cycle—the body's "internal biological clock" that regulates sleep-wake and many other processes within our bodies. The study closed with the participants having nine nights of recovery sleep at the usual time.

The researchers saw that prolonged sleep restriction with simultaneous circadian disruption decreased the participants' resting metabolic rate. Moreover, during this period, glucose concentrations in the blood increased after meals, because of poor insulin secretion by the pancreas.

According to the researchers, a decreased resting metabolic rate could translate into a yearly weight gain of over 10 pounds if diet and activity are unchanged. Increased glucose concentration and poor insulin secretion could lead to an increased risk for diabetes.

"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," said Orfeu M. Buxton, PhD, BWH neuroscientist and lead study author. "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. The evidence is clear that getting enough sleep is important for health, and that sleep should be at night for best effect."


Brigham and Women's Hospital
Science Translational Medicine
National Institute on Aging
National Heart, Lung and Blood Institute
National Center for Research Resources (Dissolved)
Center for Clinical Investigation of the Harvard Clinical and Translational Science Center
Joslin Diabetes and Endocrinology Research Center Service Specialized Assay Core
National Space Biomedical Research Institute
Natural Sciences and Engineering Research Council of Canada
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