Vitamin B12 Status and Cardiovascular Risk: Novel Insights from NMR-Based Lipoprotein Profiling in 20,665 Adults

<b>Background/Objectives:</b> Vitamin B12 deficiency affects up to 40% of certain populations worldwide and has been associated with cardiometabolic risk. However, its relationship with detailed lipoprotein subfractions remains poorly defined. This study aimed to investigate the association between serum vitamin B12 levels and atherogenic lipid profiles using NMR-based lipoprotein subfraction analysis. <b>Methods:</b> In this retrospective cross-sectional study, data from 20,665 apparently healthy adults undergoing routine health screening were analyzed. Participants were categorized into quartiles based on serum vitamin B12 levels (Q1: ≤328 pg/mL; Q4: ≥540 pg/mL). Lipoprotein subfractions were quantified using Bruker NMR spectroscopy. The Atherogenic Index of Plasma was calculated as log₁₀(triglycerides/HDL-cholesterol). Statistical analyses included ANCOVA adjusted for age, with corrections for multiple comparisons. <b>Results:</b> Higher serum B12 levels were significantly associated with a more favorable lipid profile. Specifically, AIP values decreased progressively across B12 quartiles (Q1: -0.051 ± 0.273; Q4: -0.170 ± 0.294; <i>p</i> < 0.001, partial η² = 0.017). HDL-cholesterol increased (<i>p</i> < 0.001, partial η² = 0.008), while triglycerides and VLDL-TG subfractions (VLDL1-TG: <i>p</i> < 0.001; VLDL5-TG: <i>p</i> = 0.029) declined with higher B12 levels. Among LDL subfractions, small dense LDL (LDL5-TG) exhibited a consistent inverse association with B12 (<i>p</i> = 0.002, partial η² = 0.001). These associations were robust across all age strata, with no significant interaction between B12 levels and age. <b>Conclusions:</b> Serum vitamin B12 levels are inversely associated with atherogenic lipid parameters in a large cohort of asymptomatic individuals. Higher B12 status correlates with lower AIP, reduced triglyceride-rich lipoproteins, and diminished small dense LDL particles across all age groups. These findings suggest that B12 status may serve as a potential biomarker in cardiovascular risk assessment and highlight the need for prospective interventional studies.