Association between the red blood cell distribution width-to-albumin ratio and risk of colorectal and gastric cancers: a cross-sectional study using NHANES 2005–2018

The red blood cell distribution width-to-albumin ratio (RAR) is a novel biomarker that concurrently reflects nutritional status and inflammation. Unlike traditional cancer risk markers that focus on either inflammation or nutrition independently, RAR provides a more integrated assessment of these interrelated processes, making it a promising tool for cancer risk prediction. This study aims to investigate the relationship between RAR and the risk of digestive tract tumors (DTT), with particular emphasis on colorectal cancer (CC) and gastric cancer (GC). This study explored the relationship between RAR and the risk of DTT using data from 32,953 participants in the 2005-2018 National Health and Nutrition Examination Survey (NHANES). Although weighted multivariate logistic regression models were used to adjust for potential confounders, residual confounding and selection bias may still affect the accuracy and generalizability of the findings, potentially influencing causal inferences. Additionally, subgroup analyses, interaction tests, and restricted cubic splines were performed to further examine potential associations. A two-sample Mendelian randomization analysis was also conducted to investigate the causal relationship between RAR and DTT. Among the participants, 234 were diagnosed with DTT, including 215 cases of CC and 19 cases of GC. Higher RAR levels were significantly associated with an increased risk of CC (OR = 1.48, 95% CI = 1.04-2.11, P < 0.027), but not with GC (OR = 1.33, 95% CI = 0.45-3.94, P = 0.60). A non-linear association between RAR and CC was also observed. Mendelian randomization analysis indicated that albumin was negatively associated with CC risk (OR = 0.84, 95% CI = 0.73-0.97), while erythrocyte distribution width (RDW) showed no significant association. This study reveals a significant association between RAR and colorectal cancer (CC) risk, indicating that RAR may serve as a valuable biomarker for risk stratification. For individuals with abnormal RAR values, the integration of supplementary screening tools-such as fecal occult blood testing, colonoscopy, or additional biomarkers-could enhance early detection rates for CC. This strategy would allow healthcare providers to more effectively identify high-risk individuals and tailor personalized prevention strategies.