Compared with other populations, Black Americans face a greater risk when it comes to having diabetes and colorectal cancer.
The U.S. Office of Minority Health estimates that African American adults are 60 percent more likely than white adults to be diagnosed with diabetes. Black Americans are also 20 percent more likely than most other groups to get colorectal cancer (cancer of the colon or rectum), according to the American Cancer Society.
Now new findings show that this risk of developing colorectal cancer may be more than double for some who also have diabetes.
In a study where the majority of 54,000 participants were low-income African Americans, a diabetes diagnosis was linked to a 47 percent higher risk of developing colorectal cancer compared with participants without a diabetes diagnosis.
“Type 2 diabetes and colorectal cancer disproportionately burden individuals of low socioeconomic status and African American race,” wrote Shaneda Warren Andersen, PhD, an assistant professor of population health sciences in the School of Medicine and Public Health at the University of Wisconsin in Madison, and her study coauthors. “These findings suggest that given the emerging association between diabetes and elevated risk for colorectal cancer, screening via colonoscopy for individuals with diabetes may help to mitigate risk.”
Published November 14 in JAMA Network Open, the research involved 54,597 participants from the southeastern United States, ranging in age between 46 and 58. About two-thirds were Black and 64 percent were women. More than half had an income of less than $15,000 per year.
About 300 people in 26,000 with diabetes developed colorectal cancer, compared with about 200 in 28,600 participants without diabetes.
Screening Substantially Lowers Cancer Risk
Dr. Warren Anderson and her collaborators highlighted results showing how screening through colonoscopy dramatically reduced the chances of developing cancer.
Among those with diabetes who reported having had colonoscopies, the risk of developing cancer was 18 percent higher compared with those without diabetes. This risk, however, jumped to 100 percent higher among those who had never had a colonoscopy.
“Colonoscopy is the gold standard for colorectal cancer screening tests because it normally detects colorectal cancer cancer early,” says Christine L. Sardo Molmenti, PhD, an associate professor and cancer epidemiologist in the department of occupational medicine, epidemiology, and prevention with Zucker School of Medicine at Hofstra-Northwell in Hempstead, New York. “We can prevent cancer by removing precancerous polyps, which is really the key.”
The American Cancer Society emphasizes that if colorectal cancer is found at an early stage, the five-year relative survival rate is about 90 percent — but this can drop as low as 13 percent in later stages when the cancer has spread.
Other Colorectal Risk Factors to Consider
The scientists observed that cancer risk was greater in those who had diabetes for a shorter time period compared with those who’d had it longer. The likelihood of getting a cancer diagnosis was more than double in participants with a diabetes duration of two to five years compared with those who had diabetes 5 to 10 years.
Dr. Molmenti, who was not involved in the research, speculates that someone who has had diabetes for a longer period of time may be getting more care and seeing doctors more regularly.
“They may be getting more regular screenings, which prevents cancer in the later stages, while those more newly diagnosed with diabetes might not be fully into the healthcare system,” she says.
The link between diabetes and cancer risk was also greater among former and current smokers. “Cigarette smoking is inflammatory and may exacerbate the inflammatory mechanisms of diabetes hypothesized to contribute to colorectal cancer,” wrote Warren Anderson and her coauthors.
Past research suggests that high blood sugar levels due to diabetes may help fuel the proliferation of tumor cells. Higher amounts of insulin in the blood related to diabetes may also drive cancer cell growth, per other research.
The analysis did not find a relationship between body mass index (BMI) and increased cancer risk, which Molmenti called “surprising,” as previous research has suggested that obesity may be a contributing factor when it comes to cancer.
Steps Toward Reducing Disparities in Colorectal Cancer
Based on these findings, the study authors concluded that diabetes prevention and control may help reduce colorectal cancer disparities.
Because those with colorectal cancer had lower participation in screenings, researchers indicated that better education and access to colonoscopies in the Black community could help reduce disparity.
“Colorectal cancer is probably the most preventable cancer of all the cancers that are out there, but awareness about the importance of screening is really where we have a big deficit,” says Molmenti.
For adults wanting to explore their screening options based on their risk factors, Molmenti, who is a member of the Colorectal Cancer Alliance’s Medical Scientific Advisory Committee, recommends taking an online screening quiz created by the Alliance.