# item.guide
Side-by-Side Comparison Essential Vitamins & Minerals

Vitamin B12 (Cobalamin) vs. Vitamin D3 (Cholecalciferol)

Comparing 2 standards across 9 specifications. 9 key differences identified.

Comparing:
Vitamin B12 (Cobalamin)
Vitamin D3 (Cholecalciferol)
Vitamin B12 (Cobalamin) →

Vitamin B12 is a cobalt-containing water-soluble corrinoid synthesized exclusively by microorganisms. Adult RDA is 2.4µg/day (no Upper Limit established), required for DNA synthesis, methionine synthase homocysteine conversion, and myelin sheath maintenance.

View full Vitamin B12 (Cobalamin) spec sheet →
Vitamin D3 (Cholecalciferol) →

Vitamin D3 is a secosteroid prohormone synthesized endogenously in skin via solar UVB irradiation of 7-dehydrocholesterol. Adult RDA is 600–800 IU (15–20µg), with a Tolerable Upper Limit of 4,000 IU (100µg)/day, regulating systemic calcium absorption and immune gene expression.

View full Vitamin D3 (Cholecalciferol) spec sheet →

Specification Comparison Table

9 Parameters
Parameter / Spec
Vitamin B12 (Cobalamin)
Vitamin D3 (Cholecalciferol)
Nutrient Type
Water-Soluble Corrinoid Vitamin Fat-Soluble Secosteroid Prohormone
Adult RDA / RDI
2.4 µg / day (2.6µg pregnancy, 2.8µg lactation) 600 – 800 IU / day (15 – 20 µg)
Tolerable Upper Limit (UL)
None Established (Extremely low toxicity) 4,000 IU / day (100 µg) (Endocrine Society: up to 10,000 IU safe)
Chemical Forms
Methylcobalamin (Active), Adenosylcobalamin (Active), Cyanocobalamin (Stable synthetic) Cholecalciferol (D3 - Animal/Lichen), Ergocalciferol (D2 - Fungi)
Primary Biological Function
Methionine synthase cofactor, Methylmalonyl-CoA mutase cofactor, Myelin integrity, Erythropoiesis Calcitriol receptor (VDR) activation, intestinal calcium/phosphorus absorption, antimicrobial peptide synthesis
Deficiency Condition
Pernicious / Megaloblastic Anemia, Irreversible Neurological Peripheral Neuropathy Rickets (children), Osteomalacia (adults), Immune dysregulation
Top Whole Food Sources
Oysters, Beef Liver, Sardines, Salmon, Beef, Dairy, Eggs (Absent in unfortified plant foods) Sunlight UVB, Atlantic Salmon, Sardines, Egg Yolk, Fortified Milk
Absorption Mechanism
Requires Gastric Acid, R-Protein, and Intrinsic Factor (IF) via Ileal Cubam receptors —
Target Serum 25(OH)D Level
— 30 – 50 ng / mL (75 – 125 nmol / L)

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