Friday, October 30, 2009 10 Responses
Back in June, I discussed the results of a large epidemiological study in women that showed that women with larger breasts have an increased risk of developing type-2 diabetes.
As soon as Travis and I read this study, we knew we had to do a follow-up study of our own to see if this finding was simply spurious or if there was actually something to large breasts that indicated health risk – beyond that explained by obesity per se.
The project that Travis and I began over a year ago has culminated in both a hot-off-the-press publication in the journal Obesity, as well as my presentation at this year’s Obesity Society meeting in Washington D.C.
In the study, we used body composition data acquired through MRI on about 100 premenopausal women to directly quantify breast size. By using MRI data we significantly improved the methodology used by the authors of the original study on breast size and diabetes risk, who relied on over 20 year recall of cup size as their key measure.
First, we sought to examine if breast tissue volume was associated with any cardiometabolic risk factors, such as glucose tolerance (a known antecedent to type 2 diabetes) and various blood lipids. Since the original authors found an association between cup size and diabetes risk, we expected to find an association between breast volume and cardiometabolic risk factors.
What did we actually find?
Breast volume was not associated with any of the cardiometabolic risk factors measured in any of the statistical models used. However, in these analyses, visceral or intra-abdominal fat was a strong predictor of numerous risk factors – a finding reported in numerous studies.
Next we decided to examine the associations between breast volume and other body fat depots. Here is where the story got interesting. First off, as one would predict, women with larger breasts had more subcutaneous (under the skin) fat in their thighs, abdomen, as well as more visceral and inter-muscular (or ectopic) fat. That is, bigger breasted women tended to carry more fat everywhere.
However, once we controlled for their level of obesity (body mass index and waist circumference) bigger breasted women were no more likely to have more subcutaneous fat in either lower body or abdomen, but were much more likely to have excess fat deposition in the dangerous visceral and inter-muscular depots.
Specifically, our study found that given the same age, body mass index (total obesity), waist circumference (abdominal obesity), women with the highest breast volume had approximately 1.1 and 1.3 kg more visceral fat and intermuscular fat in comparison to women with the smallest breast volume.
In other words, large breasts appear to indicate a phenotype characterized by the augmented deposition of fat in ectopic depots, such as visceral and inter-muscular fat – each of which is independently associated with increased cardiometabolic risk. The extrapolation of our findings suggests that excess visceral or intermuscular fat may be the conduit which explains the previously documented association between breast size and type-2 diabetes.
While our findings are intriguing (someone at the Obesity Society conference suggested I should get an award from the most “unique” study), there exist a couple clinical examples which corroborate our findings.
For example, approximately 40-50% of women undergoing liposuction of subcutaneous adipose tissue from the hips, thighs, or abdomen present with a paradoxical enlargement of breast size of at least one cup as well as a relative increase in visceral fat post-surgery. Additionally, highly active antiretroviral therapy among HIV-positive women is associated with a peripheral loss of functional subcutaneous fat but a compensatory increase in visceral and intermuscular fat (well documented lipodystrophy), in association with a significant enlargement in breast size.
Now before women with large breasts head out to get breast reductions, it is key to consider that our findings are quite preliminary, and furthermore that breast size only appears to be a proxy for other factors which are more likely to be causally related to health risk. Thus, further research in this area is clearly warranted before we begin screening disease risk by breast size. Nevertheless, when explaining our study findings at the conference, I heard many sighs of relief from women who perceived themselves to have smaller breasts.
Have a great Halloween weekend!
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Janiszewski, P., Saunders, T., & Ross, R. (2009). Breast Volume is an Independent Predictor of Visceral and Ectopic Fat in Premenopausal Women Obesity DOI: 10.1038/oby.2009.336
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