Nicholas M. Perry, director of The London Breast Institute at The Princess Grace Hospital in London, said that breast tissue in women may be fatty or glandular or both. Women with more glandular breasts show denser tissue on a mammogram and have nearly four times the risk of developing breast cancer than women with fatty breasts, Perry said.

The researchers analyzed digital mammograms of 972 women from urban, suburban and rural areas and found women who lived in London had significantly denser breasts than those living outside the city.

The findings, presented at the annual meeting of the Radiological Society of North America in Chicago, found the risk of increased density was twice as great in the 45- to 54-year-old group, but analyses suggest that overall differences by area were more pronounced in women under age 50. However, Perry cautioned more research is needed.

Women with dense breasts should be screened with digital mammography, which is more effective at detecting cancer in dense breast tissue, Perry advised.