Vitamin B12, also known as cobalamin, is a water-soluble nutrient essential for cellular metabolism. It serves as a cofactor in the synthesis of DNA and the metabolism of fatty acids and amino acids. The vitamin is also crucial for maintaining a healthy nervous system by supporting the formation of the myelin sheath that insulates nerve fibers. Since humans cannot synthesize cobalamin, it must be obtained through the diet. Milk has historically been a significant source of B12 for those who consume animal products.
Natural Occurrence in Dairy Milk
Traditional dairy milk is a natural source of cobalamin because ruminants, such as cows and goats, have a unique digestive process. Bacteria and archaea living in the animal’s rumen synthesize the vitamin, provided there is sufficient cobalt in the feed. This bacterially produced B12 is then absorbed by the animal and secreted into the milk.
The concentration of B12 in cow’s milk can vary significantly among different herds due to factors like the animal’s diet, genetics, and stage of lactation. Generally, a 250-milliliter glass of cow’s milk can supply a substantial portion of the recommended daily intake for an adult. Because cobalamin is water-soluble, its concentration is not significantly altered by the fat content, meaning whole, reduced-fat, and skim milk contain comparable levels. Other mammalian milks, such as those from sheep, also contain naturally occurring B12, as their digestive systems function similarly.
Fortification in Plant-Based Milks
Plant-based milk alternatives, including varieties made from soy, oat, almond, and rice, naturally contain virtually no vitamin B12. Since plants do not synthesize cobalamin, these beverages must be supplemented to serve as an equivalent nutritional source. Fortification makes these products nutritionally comparable to cow’s milk, especially for vegetarian or vegan consumers.
Manufacturers often add B12 in the form of cyanocobalamin, a stable and widely used synthetic version of the vitamin. The B12 levels in fortified plant milks are highly variable, ranging from 0.6 micrograms to over 5 micrograms per cup. Many brands aim to match or surpass the B12 concentration found in dairy milk, often providing 100% of the daily value in a single serving. Consumers must carefully check product labels, however, as many plant-based milks are still sold without any B12 fortification.
B12 Stability During Milk Processing
The nutritional value of milk is influenced by the heat treatments required for commercial safety and shelf life. Vitamin B12 is relatively heat-stable compared to some other water-soluble vitamins, but some loss occurs during processing. Pasteurization (heating milk to at least 72°C for about 15 seconds) causes minimal loss, typically less than 10% of the original B12 content. Ultra-high-temperature (UHT) processing uses much higher heat (often above 135°C) to create shelf-stable milk, leading to greater B12 losses, ranging from 10% to 20%. While initial processing losses are manageable, the vitamin can also degrade during long-term storage, with losses up to 50% reported in UHT milk stored for 90 days.