In a recent study published in JAMA Network Open, researchers determined the relationship between type 2 diabetes (T2D) and colorectal cancer (CRC) risk among low-income African-American individuals.
Study: Type 2 Diabetes and Colorectal Cancer Risk. Image Credit: Andrey_Popov / Shutterstock.com
T2D and CRC pose disproportionate burdens on African-American individuals with low household incomes. Metabolic dysregulations during diabetes could contribute to CRC cell development and proliferation by increasing oxidative stress and inflammation.
CRC shares several contributing factors with diabetes, including low economic status, smoking, obesity, and the Black race. However, modification of the relationship between diabetes and CRC risk by shared risk factors, including socioeconomic status and race, has not been extensively investigated.
About the study
The current study analyzed data from the Southern Community Cohort Study (SCCS) in the United States, which recruited individuals between 2002 and 2009. SCCS participants completed three follow-up survey-based assessments at five-year intervals through 2018.
Of 85,000 individuals, 86% were from community healthcare centers in 12 U.S. states, and 14% were recruited through telephone or email contact. At enrollment, the participants completed questionnaires concerning demographic parameters, family history of the disease, medical history, physical activity, and diet.
The participants self-documented their race and age at diabetes diagnoses. CRC was diagnosed using the International Classification of Diseases (ICD)-Oncology third edition codes.
Individuals with over two follow-up years of data, prior tumor diagnosis at recruitment, missing data on diabetes status, were diagnosed with diabetes before 30 years of age, and non-diabetics at recruitment without participation in the follow-up surveys were excluded from the study. The data analysis period was between January 2023 and September 2023.
The study exposure was a diabetes diagnosis by physicians. New-onset CRC was determined using the National Death Index linked to the cancer registries of the states.
Cox proportional hazards regression models determined the hazard ratios (HRs), adjusted for gender, education, recruitment source, CRC screening at recruitment, insurance coverage, alcohol intake, and body mass index (BMI). The relationship between diabetes and CRC risk was also assessed among subgroups based on income, sex, ethnicity and race, smoking history, and obesity.
Among 54,597 individuals, the median age at recruitment was 51 years, 64% of whom were women, 66% were African-American, and 53% had annual incomes below $15,000. Among the participants, 68% completed one or more follow-up visits, and 39% participated in the third follow-up visit. At enrollment, 20% and 28% documented new-onset and prevalent diabetes at follow-up, respectively.
Individuals with diabetes were older as compared to those with new-onset diabetes and without self-documented diabetes, with median ages of 54, 50, and 50 years, respectively. Diabetic individuals were more likely to be female, African American, less educated, obese, and have lower annual incomes as compared to non-diabetic individuals. As compared to non-diabetics, individuals with diabetes at study initiation were more likely to be heavy drinkers, current smokers, health-insured, and undergoing CRC screening.
Individuals with CRC were older, more likely to be African American, less educated, and had participated less in CRC screening as compared to those without CRC. A total of 289 diabetic individuals out of 25,992 developed CRC as compared to 197 out of 28,605 non-diabetic individuals.
Diabetes diagnosis increased CRC risk by 47%, with an HR of 1.5. These associations were more robust among individuals who did not undergo colonoscopy screening and had a history of smoking with HRs of 2.1 and 1.6, respectively.
The associations were more robust among women than men, with HRs of 1.6 and 1.3, respectively, and among individuals recently diagnosed with diabetes. As compared to five-to-ten-year diabetes duration, individuals with diabetes for two to five years were at a greater risk of CRC. CRC risk was lower among individuals with diabetes durations of 10 years or more.
Biological pathways, including hyperinsulinemia and hyperglycemia, may contribute to the association between T2D and an increased risk of CRC. CRC cells prefer a glycolytic metabolism; therefore, hyperglycemia may aid carcinogenesis by supplying the extra glucose required for cellular proliferation. Likewise, hyperinsulinemia may promote glucose absorption in cancer cells and interact with receptors for insulin to stimulate proliferative pathways and elevate CRC risk.
The study findings demonstrate that diabetes was associated with an increased CRC risk, thus indicating that glycemic control might lower CRC risk. This relationship was weaker for individuals who underwent colonoscopies, thus indicating that colonoscopy screening for diabetic individuals may help mitigate risk.