That fifth sugar-laden Coke of your all-nighter may be doing more harm than you think, a group of University researchers says. The recently released study demonstrates new links between sleep deprivation and blood-sugar control among people with diabetes.

Researchers looked at 161 black patients being treated for diabetes at the U of C Hospitals. The participants were given a questionnaire to assess sleep quality and duration. Researchers then tested the participants’ blood for glycosylated hemoglobin (HbA1c), a substance that shows a person’s average blood-glucose level over the last three months.

Only six percent of patients reported getting eight hours of sleep on a weeknight. The average was six hours. As for quality, measured using the Pittsburgh Sleep Quality Index (PSQI), 71 percent of participants received a “poor” rating.

A normal HbA1c level for a healthy adult is between four and six percent; diabetics are doing well if they keep their levels under seven. The median HbA1c score in the study was 8.3 percent.

“Our study showed that for those with diabetes, those with poor sleep quality, or insufficient sleep have on average worse blood sugar control,” said Kristen Knutson, an assistant professor and research associate in the department of health studies at the U of C and the study’s lead author.

The study, which appeared in the September 18 issue of the Archives of Internal Medicine, was co-authored by Eve van Cauter, a professor of medicine at the University; Armand Ryden, of the department of medicine at the University; and Bryce Mander of the Institute for Neuroscience at Northwestern University.

Scientists are still in the dark about why exactly a lack of sleep worsens diabetes, but Knutson believes the correlation is due to multiple factors. For example, sleep loss affects how the brain uses glucose and alters some hormone levels, both of which could cause higher blood-sugar levels. Despite this uncertainty, the practical implications of the study are real.

A general lack of sleep in society could be contributing to the current epidemic of the disease, scientists say.

“If sleep loss can lead to impairments in glucose metabolism, as many studies suggest, then the increase in the number of people with diabetes may be partially due to sleep restriction,” Knutson said.

But there’s good news, too. Knutson said that getting enough sleep could be a cheap and easy way for diabetics to help control their disease.

“Sleep need varies between individuals so there is no single number that applies to everyone…but studies have demonstrated that self-reported sleep between seven and eight hours is associated with the lowest risk of disease,” Knutson said.

The researchers say they’re not sure from their study whether a lack of sleep was causing poor blood-sugar control or the other way around.

“Future studies need to be designed with a sleep intervention,” where the effect of improved sleep quality on blood sugar in diabetics is measured, Knutson said.

For now, students planning all-nighters might want to consider switching to diet soda and bitter coffee to get their second wind.