Uncomfortable patients might want to get their colonoscopies finished as quickly as possible, but it turns out there are hazards to rushing through these cancer screenings.

A gastroenterologist at the Minneapolis VA Medical Center has found a nearly threefold higher rate of colon cancer among patients whose doctors took less than six minutes to inspect their colons when compared with patients whose screenings lasted six or more minutes.

“The colon is a tube, but it’s folded up and it has a lot of turns and twists,” said Dr. Aasma Shaukat, the chief of the Minneapolis VA’s GI section, who led the study. “It folds up like an accordion. There are a lot of things that are very easy to miss.”

Shaukat’s research group reviewed 76,810 colonoscopies provided between 2004 and 2009 at Minnesota Gastroenterology, a large private practice, and tracked the cancer histories of patients in the five years after they were screened.

Colonoscopies involve threading lighted scopes into patients’ large intestines to search for abnormal lumps or other abnormalities. Most people are told to get them after turning 50, but anyone with a family history of colon cancer is encouraged to get a screening sooner.

The overall procedure takes less than a half-hour. But the length of the exam itself is measured by the time doctors spend inspecting the inside of the colon as they gradually withdraw their videoscopes back out of patients.

Advisory boards started recommending that colonoscopies last at least six minutes several years ago, but Shaukat said this is the first research to link longer screenings with lower colon cancer risks.

However, her July study found no benefit to a colonoscopy lasting more than eight minutes, she said. “There might be a point of diminishing returns.”