Measuring a woman's breast size at age 20 may help predict whether she will develop diabetes in middle age, according to new Canadian research.
The study, published in today's edition of the Canadian Medical Association Journal, suggests that women with a bra cup size of D or larger are almost five times more likely to develop diabetes than women with an A cup.
Even after adjusting for a number of other factors that influence the risk of diabetes, such as obesity, diet, smoking and family history, the D cup women were still 68 per cent more likely to develop diabetes than women with an A cup. (Women with B and C cup sizes - the most common - saw their risk increase concomitant to cup size.)
Joel Ray, a clinician-scientist in the department of obstetrics and gynecology at St. Michael's Hospital in Toronto, said the findings are not a complete surprise, but open up some intriguing avenues for further research.
Obesity is a key risk factor for diabetes and, because breasts are principally composed of fat, women who are overweight or obese tend to have larger cup sizes.
However, the research shows that cup size is not directly correlated to body mass index, or BMI (an approximation of body fat). This raises the intriguing possibility that fat that accumulates in the breast may, like fat that accumulates in the belly, be a sort of fat-producing factory that strongly influences insulin resistance, the underlying cause of diabetes.
In fact, the research suggests that a "woman's breast size in late adolescence reflects her predisposition to insulin resistance and Type 2 diabetes" that is independent of BMI, Dr. Ray said.
If that is true, doctors will likely measure breast size the way they do belly size and view it as a red flag for diabetes and heart disease.
Dr. Ray stressed, however, that the research is preliminary and should not be acted upon at this time.
"What should women and their caregivers do with this information? Absolutely nothing," the researcher said.
More specifically, Dr. Ray said women should not think that breast reduction surgery may reduce their risk of diabetes, though he intends to study that question.Alexander Sorisky, a senior scientist in the chronic disease program of the Ottawa Health Research Institute, offered up a similar analysis.
He said that breast size may eventually prove to be a "new anatomic predictor" of Type 2 diabetes but "it's too early to tell."
Data for the new research were derived from the Nurses Health Study II, a massive research project that has been tracking the health of a large cohort of nurses in 14 U.S. states since 1989.
There were a total of 92,106 participants in the study examining the link between breast size and diabetes. During the period from 1993 to 2003, a total of 1,844 of the nurses developed the disease.
Dr. Ray and his colleagues found that the larger their bra cup size at age 20, the more likely they were to develop diabetes.
(Bra cup size is traditionally determined by measuring the horizontal chest circumference just under the breasts, adding five inches and subtracting the total from the circumference at the fullest part of the breasts. A net difference of one inch is equivalent to an A cup, and four inches is a D cup. Cup size also provides a reasonable approximation of breast volume and hence amount of fat.)
The proportion of participants with a family history of diabetes was higher among women with larger cup sizes than those with smaller cup sizes. The larger-breasted women were also more likely to have smoked.
The women with large bra cup sizes at age 20 recalled being slightly heavier at ages 5 and 10 than their less-busty counterparts.
