A new study has revealed that middle-aged or older women who have insufficient sleep every night, or two hours above the normal, could develop type-2 diabetes, RapidNewsNetwork reports.

The results of the study showed that sleeping 2 or more hours extra above normal and sleep duration of 6 hours or less, both increased risk for type 2 diabetes.

A lack of sleep may increase the risk of diabetes by reducing the body's sensitivity to insulin. On the other hand, researchers believe that long sleep denotes a sleep disorder, depression, or ill health, which increase the risk of developing diabetes.

Women who overslept by at least two hours stood a 21 percent greater risk of developing diabetes. The team found that five hours of sleep per night resulted in a 20 percent reduced insulin sensitivity.

Although the study found an association between these factors, it isn't clear whether it is a causative relation.

"We found that when people get too little sleep it leaves them awake at a time when their body clock is telling them they should be asleep," the study's lead author Kenneth Wright Jr., PhD, professor of integrative physiology at CU-Boulder and also professor of medicine at the University of Colorado School of Medicine, said, according to 9news.

"And when they eat something in the morning, it impairs their ability to regulate their blood sugar levels."

The researchers looked at a small group of healthy men and women in their study, where half the participants slept for five hours a night for five days, NDTV reports.

Then they slept for up to nine hours a night for five days. The other half of the group completed the sleep conditions in the opposite order.

The study revealed that those who slept five hours a night had a reduced sensitivity to insulin, which in time could increase the risk of getting diabetes. When the same participants slept 9 hours a night, the sensitivity to oral insulin returned.

However, it was not enough time to return to the normal level of intravenous insulin sensitivity.

The study appeared in the journal Current Biology.