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Skirt size is a better predictor of breast cancer risk than body mass index

Skirt size a better predictor of breast cancer risk than body mass index
At age 25, the average skirt size of the women in the study (as recalled and reported by them) was a U.S. 8 (U.K. 12).

Here’s yet another reason to be concerned about our expanding waistlines: A new study has found that women who gain a skirt size each decade after their mid-20s are at increased risk of developing breast cancer after menopause.

In fact, this study’s findings suggest that skirt size is a better predictor of breast cancer risk than body mass index (BMI).

For the study, which was published online this week in the journal BMJ Open, researchers analyzed three years of medical and lifestyle data collected from 93,000 women in England who were taking part in the U.K. Collaborative Trial of Ovarian Cancer Screening. Most of the women were white, had a university degree and lived in middle or upper socioeconomic areas. Most were also overweight at the start of the study, with an average BMI of 25-26. The average age at the start of the study was 64 — well past menopause.

During the period of the study, 1,090 women developed breast cancer, resulting in an absolute risk of breast cancer of 1.2 percent. As would be expected from previous research, women who had a family history of breast or ovarian cancer or who had undergone infertility treatment or menopausal hormone therapy were at increased risk of being diagnosed with breast cancer, while those who had a history of being pregnant for at least six months were at decreased risk.

Yet, even after taking into account all those known risk factors, the study found that increases in skirt size emerged as the strongest predictor of breast cancer risk.

A common experience

Three out of four of the women in the study reported that their skirt size had increased since their mid-20s. At age 25, the average skirt size of the women in the study (as recalled and reported by them) was a U.S. 8 (U.K. 12). At the start of the study, the average skirt size reported by the women was a U.S. 10 (U.K. 14).

But many of the women acknowledged that their skirt size had jumped more than one size over those four decades or so. And when the researchers analyzed the data, they found that going up a skirt size every 10 years between the age of 20 and 64 increased the women’s risk of breast cancer later in life by 33 percent. Going up two skirt sizes every 10 years increased the risk even more, to 77 percent.

Of course, those are relative risks. In absolute terms, an expansion in skirt size every 10 years increased the postmenopausal breast cancer risk from 1 in 61 to 1 in 51, the researchers explain. They also point out that putting BMI into the risk calculations did not significantly improve the prediction of risk. In other words, an increase in skirt size over a lifetime — not just skirt size at a particular point after menopause — was the better predictor of breast cancer risk.

The findings concur with other studies that have shown that an expanding midriff is associated with an increased risk of pancreatic, endometrial and ovarian cancer.

“Although the exact mechanisms of these relationships need to be better understood, there is a suggestion that body fat around the waist is more metabolically active than adipose [fat] tissue elsewhere,” the researchers write.

Caveats

Because this is an observational study — and one that relied on people’s self-reporting of past and current skirt sizes — no definitive conclusions can be drawn about cause and effect. Another major limitation of the study is the homogeneity of the participants. The findings might have been different if the study had included more racially, ethnically and socioeconomically diverse women.

Furthermore, as almost every woman knows (but doesn’t like to admit), clothing manufacturers have been quietly engaging in “size inflation” for decades in both the U.K. and the U.S. What was a U.S. size 12 in the 1980s or 1990s may now be a size 10 or 8, depending on the manufacturer.

The authors of this new study acknowledge such “vanity sizing,” but say it doesn’t affect their findings because the downsizing would have had an equal effect on the skirt-size reporting of all the women in their study — those who developed breast cancer and those who didn’t.

You can read the study in full on the BMJ Open website.

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