A new study from Europe has found that the benefits of regular colonoscopies in helping reduce the risk of colorectal cancer and death may have been overestimated due to gaps in evidence.

The Nordic-European Initiative on Colorectal Cancer (NordICC) conducted a trial involving nearly 85,000 people between ages 55 and 64. The study sample included people from countries including Poland, Norway, Sweden, and the Netherlands and was conducted from 2009 to 2014.

The trial participants were randomly assigned to receive invitations to receive colonoscopies or standard care without the screening.

An 18 percent reduction in the risk of colorectal cancer over a 10-year period was observed among those who were invited to receive colonoscopies. However, the reduction for the risk of death due to colorectal cancer in this same group was found to be “not significant” by researchers.

The study noted that these results differ from previous estimates that have associated colonoscopies with a 40 percent to 69 percent drop in the risk of colorectal cancer and a 29 percent to 88 percent drop in the risk of death.

Researchers from the NordICC trial wrote that the results were “both surprising and disappointing.”

They cited several reasons for why the risk reductions offered by colonoscopies were so low in their trial, including the lower turnout among those invited to receive the screening — 42 percent. When the estimates were based on only those who were invited to receive colonoscopies the reduction risks for colorectal cancer and deaths rose by 31 percent and 50 percent, respectively.

Colon cancers are generally believed to be slow-growing and the five-year survival rate for cases that are detected before the disease spreads throughout the body is 91 percent, according to the American Cancer Society.

Current medical guidance advises that people begin getting colonoscopies at age 45, though some should start at a younger age if they have certain diseases like Crohn’s or if colon cancer runs in their family. If initial colonoscopies do not detect signs of cancer, then most people are advised to get screened every 10 years.

If the results of this trial truly reflected the real-world efficacy of colonoscopies, researchers said other colorectal cancer screening methods could be more justifiable, like a fecal immunochemical test, which tests for hidden blood in stools that could be early signs of cancer.

However, the researchers concluded that a larger degree of high-quality colonoscopies should still result in greater reductions in colorectal cancers and related deaths.