In 2009, the U.S. Preventative Services Task Force raised the age for women to begin routine breast cancer screening to 50 from 40. The task force also found insufficient evidence to recommend for or against screening for women 75 and older.

Now, 14 years later, researchers at the Larner College of Medicine at The University of Vermont have discovered some unintended − and unwelcome − consequences from those loosened guidelines: A decline in mammography screening rates for every age group of women, including those aged 50-74 who are at the highest risk of developing breast cancer.

Sarah Nowak and Brian Sprague, who both hold doctorates, termed their findings a "spillover effect," since the revised guidelines were intended to reduce unnecessary screenings for groups less at risk, but spilled over to affect women who are at risk. Their findings were recently published in the American Journal of Preventative Medicine. 

Vermont had the second steepest decline in screenings of any state for all three age groups of women. The average decline nationwide was by 1.3% for women aged 40-49; .5% for women aged 50-74; and 1.7% for women 75 and older. In Vermont, those percentages were nearly doubled, with a 2.5% decline for women aged 40-49; a 1.2% decline for women aged 50-74; and a 2.9% decline for women 75 and older.

"While these percentages may seem small, the cumulative impact over 10 years translates to 2.4 million fewer women in the United States aged 50-74 being up to date with screening mammography," Sprague said in a news release. "The number of Vermont women aged 50-74 affected over the 10 years period is approximately 10,000 people."