Posted by Brigham and Women's Hospital April 23, 2012
Contributor: Dr. Orfeu M. Buxton is an associate neuroscientist at Brigham and Women’s Hospital (BWH). He studies the health consequences of chronic sleep deficiency, especially cardiometabolic outcomes.
You’ve often been told about the importance of getting enough sleep. But how often have you been told about the importance of when to sleep?
A Brigham and Women’s Hospital (BWH) Division of Sleep Medicine study showed that a combination of insufficient sleep and sleep patterns that disagree with our body’s biological clock (circadian rhythm) may lead to an increased risk of Type 2 diabetes and obesity. This is unwelcome news for rotating shift workers, a group particularly prone to not getting enough sleep, and, out of necessity, to sleeping at abnormal times.
A circadian rhythm is a biological process that regulates and coordinates many of your body’s functions, including metabolism. It tells your body when you should sleep and when you should eat. So, what would happen if you defied your body’s instinctive cues?
To address this question, researchers studied the impact of a rotating shift worker’s sleep schedule in a tightly controlled lab environment. At first, participants were getting an optimal amount of sleep at the optimal time – about 10 continuous hours each day, with each session starting after sunset. Next, participants were only allowed to sleep 5.6 hours each day, with the sleep occurring at varying times of day and night – to mimic the circadian disruptions that are experienced by a rotating shift worker (or someone with recurrent jet lag).
The researchers found that when the participants’ sleep, activity, and meal patterns were out of synch with circadian rhythms for three weeks, their resting metabolic rate decreased dramatically – translating into a yearly weight gain of about 10 pounds. During this same period of sub-optimal sleeping, participants’ blood sugar spiked and remained higher for hours after meals (because of poor insulin secretion by the pancreas), a telltale sign of developing diabetes.
By keeping the participants’ diet and activity levels constant throughout the study, researchers were able to determine that insufficient sleep and sleeping at abnormal times were directly responsible for lowering metabolism and raising blood sugar levels. This suggests that when our sleep schedule is dictated by factors that conflict with our body’s natural inclinations, our health suffers.
“We think these results reveal a mechanism for why, in people with a pre-diabetic condition, night workers are much more likely to progress to full-on diabetes than day workers,” said Dr. Orfeu M. Buxton, a neuroscientist at BWH and the study’s lead 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 results.”
– Chris P