Nov. 6 (HealthDay News) -- Early morning colonoscopies detect more polyps than colon cancer screenings done later in the day, and the number of polyps found decreases by the hour as the day progresses, a new study has found.

Removing polyps is believed to reduce the risk of colon cancer by 60 to 90 percent.

Researchers from the University of California, Los Angeles, analyzed data on 477 people who had colonoscopies in a one-year span at a Veterans Affairs hospital. Colonoscopies that started at 8:30 a.m. or earlier detected 27 percent more polyps per patient than colonoscopies performed at a later time, according to the study.

The improved rate in the early morning may be due to improved bowel preparation the night before, according to the researchers. They also suggested that doctor fatigue might also play a role in declining detection as the day wears on.

"We may find that setting a cap on the duration of endoscopic work shifts or other types of adjustments may be helpful," Dr. Brennan M.R. Spiegel, director of the UCLA/Veterans Affairs Center for Outcomes Research and Education and a co-author of the study, said in a UCLA news release.

He emphasized that colonoscopy is an effective way to screen for colon cancer at any time of the day and said that people should not worry about getting early morning procedures.

"The impact of appointment time for any individual is very, very small," Spiegel said. "Patients should feel confident that colonoscopy is helpful regardless of time of day and should be more focused on the quality and experience of their doctor rather than the time of their appointment."

The study is in the November issue of Clinical Gastroenterology and Hepatology.

SOURCE: University of California, Los Angeles, news release, Nov. 3, 2009