Urban Women Have Denser Breasts

This is curious.

Women who live or work in urban areas are more likely to have dense breasts than those who live in the suburbs, a finding that may suggest increased risk for breast cancer.

Women ages 45 to 54 who lived in central London were about 2.22 times more likely (95% CI: 1.05 to 4.68) to have very dense breasts than women who lived outside the city and, conversely, were less likely to have low breast density—21% versus 26% for non-city dwellers, Nicholas M. Perry, M.B.B.S., of the London Breast Institute, told attendees at the Radiological Society of North America meeting here.

“The difference between 21% and 26% may not seem like much, but it is more than a 25% increase based on the denominator figure,” Dr. Perry said.

Furthermore, 24% of women whose zip codes correlated with addresses in central London had extremely dense breasts (more than 75% fibrotic tissue) versus 19% of women living outside the city, he said.

The study doesn’t try to explain why there’s a difference - just that there is one.  But what could the “why” be?  My guess is either stress or diet.  Or… the study is flawed.