A new study concludes that people whose irregular sleep habits disrupt the body’s natural, 24-hour internal clock are at increased risk for obesity and diabetes. Those at particular risk include shift workers with overnight jobs and travelers who experience recurrent jet lag.
The study by investigators at Brigham and Women’s Hospital in Boston was the first to simulate in the laboratory the health effects of long-term sleep deprivation.
At the beginning of the six-week experiment, 21 healthy volunteers enjoyed optimal sleep periods of 10 hours a night, reflecting the normal sleep-wake rhythm that is controlled by the human body's internal, or circadian, clock.
This was followed by a three-week period in which the participants slept only 5.6 hours in a 24-hour period during all times of the day and night, simulating shift work.
Throughout the study, the participants’ blood sugar or glucose was measured after each meal. Glucose is used by the body as fuel. It becomes elevated in people with diabetes, explains the study's lead author, Orfeu Buxton of the Division of Sleep Medicine at Harvard University.
“Glucose at high levels is toxic," said Buxton. "It causes hypertension, neurotoxicity and a bunch of other things that are hallmarks of the diabetes condition. And what we saw is that three of 21 of our subjects, they actually met clinical criteria that would be called pre-diabetic.”
In the final, restorative phase of the study, in which the participants returned to a regular pattern of night-time sleep for nine days, their blood sugar levels returned to normal.
Buxton says a previous study he conducted showed that a disruption of the circadian rhythm led to insulin resistance, in which the hormone insulin, produced by the pancreas, is unable to transport glucose efficiently into cells, leading to dangerous levels of glucose circulating in the bloodstream.
The findings, Buxton believes, provided new evidence that repeated interruption of the body’s normal sleep-wake cycle can lead to a decrease in so-called resting metabolism, or the rate at which the body burns calories to maintain itself. Buxton says the result could be a yearly weight gain of more than 4.5 kilograms, a risk factor for diabetes.
“In this study, we showed that resting metabolic rate decreased by about eight percent," he said. "That may seem like a small number but if diet and activity are unchanged, that corresponds to about 10 to 12 pounds of weight gain in a year.”
The study on disrupted sleep and the onset of diabetes by Orfeu Buxton and colleagues is published in the journal Science Translational Medicine.
