Factcheck: does increasing skirt size increase breast cancer risk?

Research on the relationship between breast cancer risk and weight gain (with skirt sizes used as an indicator) was reported extensively last week.

From the headlines you could be forgiven for thinking that going up a single size meant a higher risk of breast cancer  ("going up one skirt size increases risk of breast cancer in over-50's") or that larger skirt sizes were in themselves a risk factor ("the risk of breast cancer increases with skirt size").

What the research - from the Institute of Women's Health at University College London - actually found was that there was an increased risk of breast cancer associated with multiple increases to an individual's skirt size, not merely having a larger skirt size, and only when the increases were sustained over three or more decades. In practice this would mean  increasing from size 10 to size 16 between your mid-20s and mid-50s, or from size 14 to size 20.

Most of the articles did go on to explain this, but the range of headlines shows that the message was not as easily understood as the researchers had hoped.

Going up one skirt size every 10 years was associated with a 33% greater risk of developing breast cancer after the menopause. Going up two skirt sizes each decade over the same period was associated with a 77% greater risk.

While those are big increases, the absolute risk of developing breast cancer over a five year period post-menopause  - according to the study - remains small. The average woman goes up by barely a third of a skirt size every decade, and faces a 1% chance of developing breast cancer. That means women putting on a whole size each decade have a roughly 1.33% chance of developing it. The overall risk for women in the UK developing breast cancer at any point in their lifetime is 12%.

Image credit: Colin Charles