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 Wednesday 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.

“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 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.

The effects were reversible after nine days of recovery sleep and the readjustment of the body’s internal clock, the study showed.