Elevated Methylmalonic Acid, a Marker of Functional Vitamin B12 Deficiency, Is an Independent Predictor of Cardiovascular Risk in Beninese Taxi-Motorbike Drivers

Background: Taxi-motorbike drivers (TMDs) in Benin constitute an occupational group with significantly elevated cardiovascular disease risk. However, the relationships between nutritional status, metabolic biomarkers, and predicted cardiovascular risk in this population remain poorly characterized. Notably, functional vitamin B12 deficiency indicated by elevated methylmalonic acid (MMA) levels, rather than plasma vitamin B12 concentrations alone, may represent an important modifiable factor contributing to cardiometabolic dysregulation in this high-risk cohort. This study aimed to evaluate the association between MMA levels and predicted cardiovascular risk, as measured by the Framingham Risk Score (FRS) among TMDs in Cotonou, Benin. Methods: A cross-sectional cohort of 176 TMDs (mean age 39.3 ± 7.7 years) underwent clinical and biochemical assessments including blood pressure, glucose, lipids, uric acid, homocysteine, folate, vitamin B12, and MMA. Participants were stratified by MMA tertiles to evaluate relationships with cardiometabolic factors. The FRS was categorized into low-risk (<10%) and elevated-risk (≥10%) groups to enhance analytical clarity and clinical interpretability. Multivariable logistic regression models adjusted for demographic, metabolic, renal, and nutritional confounders investigated the association between MMA and elevated FRS. Results: The cohort exhibited elevated homocysteine levels, with a mean of 29.4 μmol/L, and had an average FRS of 7.4%. MMA levels were elevated (mean: 183.2 nmol/L) despite normal plasma vitamin B12 (mean:424.1 pmol/L). Stratification by MMA tertiles showed a significant graded increase in FRS (T1: 6.0%, T3: 8.6%, p = 0.003) and corresponding inverse vitamin B12 levels (T1: 456.7 pmol/L, T3: 349.7 pmol/L, p < 0.001). No significant differences were observed in other cardiometabolic parameters across MMA tertiles. In fully adjusted models, participants in the highest MMA tertile (>197 nmol/L) had nearly sevenfold greater odds of elevated FRS compared to the lowest tertile (aOR = 6.99; 95% CI: 1.20 - 30.67; p = 0.030). Conclusions: This study identifies a strong and independent association between elevated MMA levels and increased predicted cardiovascular risk among TMDs in Benin. This finding highlights elevated MMA as a significant and independent contributor to cardiovascular risk in this population and supports its potential as a valuable biomarker for improving risk assessment in underserved, high-risk groups like TMDs. Further investigation