Researchers documented what many doctors had reported anecdotally following the March 7, 2000, broadcast: that Couric succeeded in encouraging others to follow her.
In a survey of 400 gastroenterologists in 22 states, the number of colonoscopies rose from an average of 15 per month before Couric's test to 18.1 per month after, researchers at the University of Michigan Health System and the University of Iowa found.
Separately, a study of Midwestern HMO members found the number of colonoscopies rose from 1.3 per 1,000 people each month before Couric's test to 1.8 per 1,000 after.
The study was published in the Archives of Internal Medicine.
The researchers compared 20 months of data before Couric's test to nine months after, so they don't know how long-lasting the "Couric effect" was.
"This is obviously very gratifying to me because it's a subject I care deeply about," Couric said. "I was very pleased to see that it's having a positive impact. Of course, we have a long way to go."
Couric has advocated colon cancer screening since her husband, TV legal analyst Jay Monahan, died of the disease in 1998. Two years later, "Today" was showing viewers images of Couric's colon, or large intestine, taken from a long fiber-optic tube.
Although researchers would not estimate how many tests were taken with Couric in mind, the results indicate that celebrity messages can be extremely effective in promoting public health, said Dr. Mark Fendrick, a University of Michigan doctor who led the research team.
Public health campaigns should consider investing more into the kind of PR campaigns that work for soft drinks and tennis shoes, he said.
Couric hasn't taken another on-air test, but "Today" continues to air stories on colon cancer once a year. She founded the National Colorectal Cancer Research Alliance, and the Jay Monahan Center for Gastrointestinal Health in New York.
She said she continues to get heartbreaking e-mails from viewers who learned too late they have the disease.
"It's one of those cancers you can have when you're feeling perfectly healthy," she said. "So before you're symptomatic, that's when you need to be screened. So I'm hoping I can increase the percentage even more."