Lack of sleep or erratic slumber from working late-night shifts or travel may lead to diabetes and obesity, according to a Harvard study that is the first to tie abnormal sleep patterns to disease.
In a trial of 21 men and women observed in a sleep laboratory, those allowed only 5.6 hours of sleep in a 24-hour period over three weeks had a slowdown in their metabolism and a reduction in insulin production. Those changes can lead to weight gain and increased blood sugar, according to research published today in the journal Science Translational Medicine.
Sleeping, eating and being active at times that are at odds with the body’s internal clock, called circadian disruption, may raise the risk of diabetes and obesity as metabolic changes occur, said Orfeu Buxton, the lead study author. More research is needed to understand the results, he said.
“We disrupted not just the timing of sleep but the timing of meals, so it seems that eating meals at an unusual time may also play a role,” said Buxton, as assistant professor at Harvard Medical School and an associate neuroscientist at Brigham and Women’s Hospital in Boston, in an April 9 telephone interview. “If you’re going to work at night, you might want your biological clock to join you on shift and have your biological daytime be during that night shift.”
About 15 percent of full-time wage and salary workers in the U.S. work an alternative shift, 4.7 percent work evenings, 3.2 percent work nights and 2.5 percent work rotating shifts, according to 2004 data from the Bureau of Labor Statistics, the latest year for which data is available. Allowing workers to stay in the same shifts for longer periods rather than changing every few days may help them stave off health problems, Buxton said.
Researchers in the study followed healthy men and women who were kept in a controlled environment. The amount of sleep, when the sleep occurred, activities and diet were regulated. For three weeks they were only allowed to sleep for 5.6 hours in any 24-hour period. The sleep occurred at all times of the day and night to help copy the schedule of rotating shift workers.
Chronic sleep restriction and disruption to the body’s internal clock caused about a one-third decrease in insulin secretion after a standard meal, the researchers found. Too little insulin raises glucose levels in the body for longer periods of time, and may increase the risk of diabetes, Buxton said.
He speculated that the clock in the pancreas, which regulates insulin, similar to the circadian clock in the brain, might also be disrupted making it not ready to secrete enough insulin to the body at the new time, he said.
Change in Metabolism
Participants also experienced an 8 percent drop in resting metabolism, the amount of calories burned by the body’s muscle excluding exercise. The slowed metabolism could contribute to a 12.5-pound increase in weight over a year if there were no changes in exercise levels or food intake. That weight gain may lead to obesity and elevate diabetes risk, the authors said.
Buxton said changes in the body’s clock and lack of sleep may cause the body to conserve energy when it isn’t necessary. Those who don’t get enough sleep also don’t exercise, eat more and eat more inappropriate foods, he said.
The effects were reversible after nine days of recovery sleep and the readjustment of the body’s internal clock, the study showed.