A new study found that middle-aged or older women who sleep six hours or less a night or oversleep by two hours or more are increasing their risk of developing type-2 diabetes.

Dr. Elizabeth Cespedes from Harvard T.H. Chan School of Public Health worked with her colleagues in a study involving 59,031 women aged 55 to 83. They reviewed the 14-year data that recorded the participants' self-reported sleep duration, diet, physical, activity and other factors every two to four years.

The researchers narrowed their analysis on 3,500 women who were diagnosed with type-2 diabetes between 2000 and 2012. Using a computer model, they were able to calculate the diabetes risk of the participants depending on sleep patterns.

The analysis showed that middle-aged and older women who sleep six hours or less are increasing their risk of developing type-2 diabetes by 15 percent while those who oversleep by at least two hours increased the risk by 21 percent.

"Chronic short sleep duration and increases in sleep duration are associated with increased risk of diabetes. Decreases in sleep duration have modest, adverse associations with diet quality and physical activity, while increases in sleep duration have modest, adverse associations with weight gain. Ongoing trials will provide further insight as to whether changes in sleep duration influence energy balance," the authors said in a news release.

The researchers clarified that their findings do not confirm a cause-and-effect connection between sleep pattern and type-2 diabetes, but rather an association.

"Some scientists argue that long sleep is a symptom of underlying sleep disorders, depression or ill health, and that it is these factors, and not long sleep, that increase the risk of diabetes," Cespedes said to HealthDay News.

The study was published in the Nov. 2 issue of the journal Diabetologia.