Chlorella vulgaris supplementation at 1g twice daily increased serum vitamin B12 levels from baseline to 214.4 ng/mL compared to 55.9 ng/mL in placebo controls after 12 weeks in 46 adults with deficiency. The algae treatment showed no adverse effects on liver or kidney function. This finding addresses a critical gap for vegans and vegetarians, who commonly develop B12 deficiency due to limited animal product intake. However, the results present a puzzle within established B12 research. Most studies indicate that algae-derived B12 exists primarily as pseudovitamin B12 analogs that don't function like true B12 in human metabolism. The study's failure to show improvements in functional B12 markers like methylmalonic acid or homocysteine—despite dramatic serum increases—suggests the measured B12 may include inactive analogs. This disconnect between serum levels and metabolic markers warrants scrutiny. As an unreviewed preprint, these findings require peer validation and replication before recommending Chlorella as a reliable B12 source for plant-based populations.