Vitamin B12 Content in Milk
Cow's milk contains approximately 3 nM (nanomolar) of vitamin B12, with one 250 mL glass providing 23-40% of the recommended daily allowance of 2.4 μg for adults. 1, 2
Specific B12 Concentrations in Milk
- Cow's milk contains approximately 2,300-3,900 pg/mL (picograms per milliliter) of vitamin B12, with significant variability between herds and individual cows 2
- One 8-ounce (250 mL) glass of milk provides approximately 50% of the RDA (2.4 μg/day) for adults, making it a rich source of this essential vitamin 1, 3
- Among individual cows, one glass of milk can provide between 16-57% of the recommended daily allowance, demonstrating substantial variation 2
Bioavailability and Absorption
Vitamin B12 from cow's milk is substantially more bioavailable than synthetic cyanocobalamin supplements, with an intestinal absorption efficiency of 8-10% 3. This superior bioavailability occurs because:
- Vitamin B12 in cow's milk is bound to transcobalamin (TC) and casein proteins, which rapidly dissociate at stomach pH (pH 2) with a half-reaction time of less than 1 minute at body temperature 4
- The TC-vitamin B12 complex from cow's milk is readily susceptible to digestive enzymes (trypsin and chymotrypsin), facilitating transfer to human intestinal absorption carriers 4
- Net intestinal absorption (measured as portal-drained viscera flux) after milk ingestion is positive and significantly greater than after equivalent amounts of synthetic cyanocobalamin 3
Factors Affecting B12 Content
Vitamin B12 concentration in milk remains relatively stable across most variables but shows some important variations:
- Breed, season, stage of lactation, and parity (primiparous vs. multiparous) do not significantly affect milk B12 concentrations in Holstein cows 2, 5
- Jersey cows produce milk with the lowest vitamin B12 concentrations compared to Holstein cows 2
- Dietary factors influence milk B12 content: higher acid detergent fiber content correlates with increased milk B12, while higher crude protein content correlates with decreased milk B12 2
- Genetic selection could potentially modify milk vitamin B12 concentration, with heritability estimated at 0.23 2
Processing Effects
Thermal processing and other food preparation methods typically reduce vitamin B12 content in dairy products 6. However, the specific magnitude of loss varies by processing method.
Comparison to Other Sources
Milk and dairy products contain much lower quantities of vitamin B12 compared to organ meats (liver and kidney), which have the highest concentrations among ruminant foods 6. Despite this, milk remains an important dietary source because it is consumed regularly and in larger quantities than organ meats 1.
Clinical Significance
The Dietary Guidelines for Americans (DGA) recommend 3 cup-equivalents per day (710 mL) of fat-free or low-fat dairy for adults, which would provide substantial vitamin B12 along with other essential nutrients including calcium, phosphorus, vitamin A, vitamin D, riboflavin, potassium, zinc, choline, magnesium, and selenium 1.