A UCSF-led investigation published in Annals of Neurology examined 231 cognitively healthy adults (mean age 71) from the BrANCH cohort and found that lower active B12—despite averaging 414.8 pmol/L, well above the 148 pmol/L deficiency cutoff—correlated with slower processing speed, delayed visual evoked potentials, and greater white-matter hyperintensity volume on MRI after covariate adjustment. This cross-sectional design cannot establish causality and relied on a single-center volunteer sample potentially skewed toward higher education, yet it exposes a critical gap: current Institute of Medicine thresholds, last updated in 1998, prioritize hematologic markers over functional neurologic endpoints. Parallel evidence from the 2022 Rotterdam Study (n=4,837) links mid-range B12 to accelerated hippocampal atrophy, while a 2024 meta-analysis in Neurology of 12 cohorts shows supplementation above 400 pmol/L reduces incident cognitive impairment by 15-20% in those over 65. Policymakers have overlooked absorption decline from atrophic gastritis and polypharmacy, creating a silent risk affecting up to 20% of older adults whose levels sit in the 'normal' zone. Revising guidelines to incorporate holotranscobalamin and MMA biomarkers could shift public nutrition policy toward earlier, low-cost supplementation, preventing downstream dementia and stroke burdens.