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Diagnosis of type 2 diabetes was associated with a higher risk for colorectal cancer (CRC) in a large, prospectively followed U.S. cohort of mostly Black adults with low socioeconomic status.

Among over 54,000 participants in the Southern Community Cohort Study, 66% of whom were Black and 53% of whom had an annual income less than $15,000, diabetes was associated with increased CRC risk (HR 1.47, 95% CI 1.21-1.79), reported Shaneda Warren Andersen, PhD, of the University of Wisconsin-Madison, and colleagues.

The associated risk was even higher in certain participants, they noted in :

• Those who had not undergone a colonoscopy (HR 2.07, 95% CI 1.16-3.67)
• Those with a history of smoking (HR 1.62, 95% CI 1.14-2.31)
• Those with recent diabetes diagnoses (diabetes duration <5 years compared with 5-10 years: HR 2.55, 95% CI 1.77-3.67)

"Our finding that shorter duration of diabetes is associated with elevated CRC risk may be partially attributable to increased interactions with the healthcare system after diabetes diagnosis, allowing for cancer screening opportunities," Andersen and team wrote. "The increase in CRC testing may initially increase CRC through the detection of prevalent CRCs and over the long term may result in reduced risk of CRC due to screening's preventive function against CRC."

"Increased interactions with the healthcare system following a diabetes diagnosis, including increased referrals to CRC screening, may be important for mitigating the harm of diabetes-related metabolic dysfunction, particularly in early diabetes, on CRC risk," Andersen and team concluded.

Previous have pointed to a link between diabetes and a greater risk of CRC, potentially due to diabetes-related hyperglycemia and hyperinsulinemia, which may support the growth of cancer cells. In addition, hyperinsulinemia may increase risk of CRC by "facilitating glucose uptake in tumor cells and by interacting with insulin receptors to activate proliferative signaling pathways," they noted.

In an email to MedPage Today, Robert Gabbay, MD, PhD, chief scientific and medical officer of the American Diabetes Association, wrote, "Sadly, this is not so surprising. People with diabetes, and in particular those with obesity, are at increased risk for a series of different cancers."

This study "highlights the importance of ensuring appropriate screening for colorectal cancer," he added. "Being able to identify precancerous lesions and ensure close follow-up is a very effective way to lower the risk of colorectal cancer."

This study used data on 54,597 people in the Southern Community Cohort Study, which recruited participants in 12 southeastern states from 2002 to 2009, who then completed three follow-up surveys by 2018. Most of the participants were recruited from community health centers. Median age at enrollment was 51 years, and 64% were women.

Participants self-reported physician's diagnosis of diabetes and racial identity. A diagnosis of CRC was identified via state cancer registries and the National Death Index.

Of the 25,992 participants with diabetes, 289 developed CRC compared with 197 of the 28,605 participants without diabetes.

Consistent with , the researchers did not observe effect modification by body mass index for the association between diabetes and CRC risk.

Andersen and team noted that "undiagnosed diabetes within the study population is a significant issue in diabetes research and may attenuate associations toward the null."

In addition, the study relied on self-reported diabetes diagnosis instead of medical records or blood testing, which is a limitation.

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