CHICAGO, June 14 (Xinhua) -- Sleeping with light on can raise the risk of diabetes, a recent study of Northwestern University (NU) shows.

NU researchers recruited 20 healthy adult volunteers aged 18 to 40, who spent two nights and three days at the lab. The first night, they slept in pitch black darkness; the second night, half of them slept in the dark again while the other half slept in a room with a bright overhead light on.

While the volunteers slept, the researchers tracked the volunteers' vital signs, brain wave activity, and leg and eye movements. They also took hourly blood samples to measure melatonin. In the morning, the researchers conducted glucose tolerance tests on the volunteers.

Results show that a single night of light exposure during sleep acutely impacts measures of insulin resistance, a risk factor for diabetes.

"These results are important given the increasingly widespread use of artificial light exposure, particularly at night," said lead author Ivy Cheung Mason, a postdoctoral fellow at NU's Feinberg School of Medicine.

"The effect we see is acute; more research is needed to determine if chronic overnight light exposure during sleep has long-term cumulative effects on metabolic function."

According to U.S. National Sleep Foundation's statistics for 2014, 35 percent of Americans report sleep quality as "poor" or "only fair", while 20 percent of Americans reported that they did not wake up feeling refreshed on any of the past seven days.

Overall, sleep disorder affects more than 25 percent of the general population and up to 50 percent of older adults worldwide.

The study has been published in an online supplement of the journal Sleep.