Young women with larger breasts may be at a higher risk of diabetes in adulthood, a Canadian study suggests.

The study, published in the Jan. 29 issue of the Canadian Medical Association Journal, found the larger a woman's bra cup size is at age 20, the greater her risk of developing Type 2 diabetes later in life.

Working with the U.S.-based Nurses' Health Study II, which started in 1989 and tracks 116,609 women from 14 states with biennial questionnaires on their health and lifestyles, the Canadian researchers assessed the onset of Type 2 diabetes between 1993 and 2003 in 92,106 participants. They excluded participants who did not include information about breast size or body mass index as well as those already diagnosed with diabetes.

They found the age-adjusted risk of developing Type 2 diabetes was two times higher for a B cup, four times higher for a C cup and five times higher for a D cup or larger than for women with the smallest cup size.

After adjusting for conventional risk factors such as family history, diet and exercise, they found the risk to be 1.3 times higher for women with a B cup at 20 compared to women who wore an A cup. For women with C and D cups, the risk was found to be 1.7 and 1.6 times higher respectively.

The study also suggests that women with the largest cup sizes develop diabetes on average about two years earlier, at age 44, than those with the smallest cup size, at 46 years.

Researchers say this is the first study to look at the link between breast size and diabetes.

"The scientific community has long cited the role of obesity as an established risk factor for Type 2 diabetes," said study lead Joel Ray, a physician at Toronto's St. Michael's Hospital, in a release. "While an elevated body mass index (BMI) and the distribution of fat around the abdomen are strongly linked to the onset of Type 2 diabetes, little is known about the impact of breast fat.

"Our study's significant findings suggest a fair correlation between the two, independent of other important factors such as BMI and waist size, and the need for further targeted research," he said.

He said follow-up research is planned to see if breast reduction surgery causes any change in insulin resistance.

Doctors question whether large breasts carry particular risks or whether it is another sign of being overweight, a risk factor for the disease.

Dr. Thomas Ransom, an endocrinologist with Halifax's Queen Elizabeth II Health Sciences Centre says bra cup sizes are a marker of obesity.

"It's not so much the big breast size of itself, but I think women who are overweight or obese should be concerned. And this is just another marker," he told CBC News. "It sort of correlates and it's really not a surprise."

He said waist circumference is a stronger indicator of Type 2 diabetes risk.