Do Big Breasts Up Diabetes Risk?

It might be seen as a vindication for small-breasted women everywhere.

After suffering through decades of bra-cup envy, those with diminutive décolletages in their late teens and early 20s may enjoy a lower risk of developing type 2 diabetes later in life than their fuller-chested counterparts — or at least, that's what a new study suggests.

But many doctors caution that the conclusions of this new research may have more to do with obesity — and therefore bigger breasts — than they do with breast size alone.

Researchers at Harvard University and the University of Toronto surveyed 92,106 women who participated in the Nurses' Health Study, asking each of the participants to recall her bra size at the age of 20. The average age of the women participating in the study was 38.

Results showed that, compared with women who recalled having an A cup or smaller at the age of 20, women who recalled having a D cup or larger had about three times higher risk for developing type 2 diabetes.

The results also showed that women who reported wearing B cup and C cup bras experienced a higher risk for the development of diabetes than women who wore an A cup — even after figuring in age, body mass index (BMI), waist circumference, eating habits, family history of diabetes, physical activity level and pregnancies.

The findings were published Monday in the Canadian Medical Association Journal.

Although researchers involved with the study said it's still unclear how breast size could be tied to diabetes risk, lead study investigator Dr. Joel Ray, an assistant professor and clinician scientist in the division of endocrinology and metabolism at the University of Toronto, believes the correlation has something to do with how breasts develop during puberty.

"Breast development is a hallmark of puberty, and we know the onset of puberty occurs earlier in obese girls," Ray explained. "But in addition to puberty and breast development beginning earlier [in obese girls], we believe the overall effect of it may be more pronounced as well, in the sense that overall net production of breast is greater."

Supporting this idea is the fact that puberty, in addition to being a time for breast development, is also a period marked by raised insulin resistance, which corresponds with the infamous middle school growth spurt.

Ray said that just as breast development is both accelerated and more pronounced in obese girls, so may be their levels of insulin resistance — a cornerstone for the development of type 2 diabetes.

However, many experts remain unconvinced of the study's findings and question why they should be asked to abandon the tried-and-true methods of evaluating patients' type 2 diabetes risk simply by calculating their BMIs and evaluating their lifestyles.

"In reality, obesity is a major determinant of risk for diabetes," said Dr. Lewis Kuller, professor and chair in the department of epidemiology at the University of Pittsburgh. "Breast size, generally, is highly correlated with body size and body fatness, since what you're storing in the breast is mainly fat tissue."

And in light of this, Kuller said, breast size may simply tell us something we already know about diabetes risk.

"It's not like we don't already have a measure for how fat someone is," he added. "You can tell just by looking in the mirror. You're not gaining some new knowledge from evaluating your breast size 20 years ago that you couldn't already predict just by looking in the mirror."

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