What Vitamins Are in Milk? B Complex, A, and D

Cow’s milk delivers a surprisingly wide range of vitamins, with its strongest contributions coming from three groups: the B-complex family (especially riboflavin and B12), vitamin A, and vitamin D. Some of these are naturally present in the milk itself, while others, particularly vitamin D, are mainly there because of fortification programs that began decades ago. How much of each vitamin actually ends up in your glass depends on fat content, how the milk was processed, how it was stored, and even what the cow was eating.

The B-Complex Vitamins in Milk

Milk is one of the richest everyday dietary sources of several B vitamins, and researchers have developed methods to measure more than 20 distinct B-vitamin forms in a single small sample of fresh milk from cows, goats, and buffalo.¹ The standout player is riboflavin (B2), which gives milk its faint yellowish-green tint under certain light. A single cup of whole milk covers roughly half a typical adult’s daily riboflavin needs, and because riboflavin is water-soluble, it stays in the liquid even when fat is removed. The concentration of vitamins B1, B2, and B7 can shift depending on whether cows graze on pasture or eat a mixed indoor ration, with grass-fed and clover-fed herds producing milk with higher levels of those three.²

Vitamin B12 deserves special attention. Milk is considered an abundant source of bioavailable B12, where the vitamin rides through your gut attached to a carrier protein called transcobalamin. Research has shown that this transcobalamin-B12 complex from cow’s milk can be absorbed by human intestinal cells, offering a natural alternative to free B12 supplements for people with certain absorption difficulties.³ Once milk hits your stomach’s acidic environment, the transcobalamin-B12 complex breaks apart quickly, and the freed B12 transfers to human carrier proteins within minutes.⁴ Some B12 also binds to the casein protein in milk, and both forms appear to be highly available for absorption in cow’s milk specifically. Interestingly, buffalo milk uses a different binding protein that may limit B12 availability somewhat.

Milk also supplies smaller but meaningful amounts of niacin (B3), pantothenic acid (B5), B6, folate (B9), and biotin (B7). None of these individually make milk the best dietary source for that particular vitamin, but together they contribute to the broad micronutrient package that makes milk nutritionally dense.

Vitamin A and the Fat Connection

Vitamin A in milk is a fat-soluble vitamin, and its location tells you a lot about how it behaves. Research has pinpointed that virtually all the vitamin A in milk sits within and on the surface of fat globules, with negligible amounts floating free in the watery serum.⁵ Some of it lodges in the fat globule core, and a portion associates with the membrane that surrounds each globule. This detail matters in a very practical way: when you skim the fat off milk, you strip out the vitamin A along with it.

That is why skim and low-fat milks sold in the United States and Canada are typically fortified with vitamin A after processing. The fat removal that creates 1% or skim milk would otherwise leave almost none of the original vitamin A behind. Whole milk retains its natural vitamin A, largely in the form of retinyl palmitate. In the U.S., a cup of whole milk provides roughly 5-10% of the daily value for vitamin A without any added fortification, though exact numbers vary with the cow’s diet, breed, and season.

Vitamin D in Milk Is Mostly Added

This is where many people’s assumptions fall apart. The natural vitamin D content of cow’s milk is very low. Detailed measurements using sensitive laboratory methods found that whole milk with about 3.8% fat contained only around 0.2 micrograms per liter of vitamin D3, and fat-reduced milks (0.1% and 1% fat) fell below detection limits entirely.⁶ An Italian study of high-quality cow’s milk found the vitamin D3 content ranged from undetectable to 17 micrograms per liter, but most samples were at trace levels or absent altogether.⁷ Raw farm milk samples in that study were also below the quantification limit. The amount of natural vitamin D correlates with the fat content of the milk, which makes sense given it is fat-soluble.

What made milk synonymous with vitamin D in most people’s minds is fortification. In the early twentieth century, rickets was widespread in northern cities where children had little sun exposure. The disease caused skeletal deformities, growth retardation, muscle weakness, and seizures. The introduction of sensible sun exposure advice combined with the fortification of milk with vitamin D nearly wiped out rickets in developed countries.⁸ Today, in the U.S. and Canada, most fluid milk is fortified to contain about 100 IU (2.5 micrograms) of vitamin D per cup.

But fortification is not always as precise as you might expect. A survey of retail milk in Ontario found that only about 20% of skim milk and 20% of whole milk actually contained the recommended vitamin D levels, with 2% fat milk doing somewhat better at 40%. Vitamin A fortification compliance was also uneven, with 46% of skim and 77% of 2% fat milk meeting targets.⁹ This variability means that what the label promises and what ends up in the carton are not always identical.

What Breed, Season, and Feed Change

The vitamin profile of milk is not fixed. It shifts with environmental and genetic factors. Evidence shows that breed differences among dairy cows affect milk’s vitamin D concentration, and dietary sources of vitamin D fed to the cow also play a role.¹⁰ Cows with more sun exposure or those fed vitamin D-enriched diets tend to produce milk with slightly higher natural levels. Seasonal variation is real: summer milk from pastured cows generally contains more fat-soluble vitamins than winter milk from housed animals, though the magnitude of the difference is usually modest enough that fortification still dominates the final vitamin D content in retail cartons.

The B vitamins respond to diet as well. Cows grazing on grass or clover pasture produced milk with significantly higher concentrations of vitamins B1, B2, and B7 compared to cows on a total mixed ration fed indoors.² These differences can carry through into dairy ingredients derived from the milk. If you are buying milk labeled “grass-fed” and wondering whether it is nutritionally distinct, the B-vitamin profile is one area where the answer appears to be yes, at least in some measurable way.

How Processing Affects What Reaches Your Glass

Most milk undergoes heat treatment before it reaches the store. The good news is that standard pasteurization, the kind labeled HTST (high-temperature, short-time, typically around 75-77°C for 15 seconds), does not cause significant losses of vitamins B1, B2, B12, or E.¹¹ Higher-temperature pasteurization is where you start to see damage: so-called high pasteurization caused a loss of about 6% in B1, roughly 4% in B2, and a more substantial 23% in B12. UHT (ultra-high temperature) processing had more variable results depending on the method used. Direct UHT and ESL (extended shelf life) treatments caused small but significant drops in B2, while indirect UHT showed no significant loss in any of the vitamins measured.

The takeaway is straightforward. If you are buying standard pasteurized milk from the refrigerator case, its B-vitamin content is essentially the same as raw milk’s. If you prefer shelf-stable UHT milk, you might lose a small fraction of riboflavin, but the difference is minor. The one processing method that genuinely dents your B12 is high pasteurization, which some specialty or organic brands use for extended refrigerated shelf life.

Light Exposure Is a Bigger Threat Than Heat

Here is something most people do not think about: the lights in your grocery store’s dairy case can degrade milk vitamins faster than pasteurization does. Riboflavin acts as a photosensitizer, meaning it absorbs light energy and kicks off oxidation reactions that break down both itself and other compounds. Vitamin A and riboflavin are both easily degraded by UV light, and the fluorescent lights common in retail dairy displays accelerate these reactions.¹² Switching to LED lighting, which many stores have done, helps: one study found no significant reduction in riboflavin or vitamin A from LED exposure compared to the non-light-exposed control, whereas fluorescent light caused measurable losses.

The fat content of milk also influences how fast light destroys its vitamins. When researchers exposed milks of different compositions to fluorescent light, vitamin A and riboflavin disappeared faster in skim milk than in whole milk.¹³ Higher light intensity accelerated the loss of both vitamins, and riboflavin degraded at a greater rate than vitamin A. Higher-color-temperature LED lights, which emit more blue-spectrum wavelengths that overlap with riboflavin’s absorption range, also led to lower retention of both riboflavin and vitamin A.¹⁴

The practical lesson: opaque containers protect vitamins better than translucent jugs. If your milk comes in a clear plastic container, storing it toward the back of the fridge where less light hits it makes a real difference. And the longer milk sits under bright lights at the store, the more riboflavin and vitamin A it loses before you even bring it home.

What Happens to Vitamins in Yogurt, Kefir, and Cheese

Fermenting milk changes the vitamin picture in ways that depend on the microbes doing the work. A classic Swedish study found that fermented milk products showed an increase in folic acid content, with ropy milk (a traditional Scandinavian product) exhibiting a twofold increase, while B12 decreased slightly.¹⁵ Other B vitamins were affected only slightly by fermentation. The drop in B12 makes sense: some of the bacterial cultures used in fermentation consume B12 as they grow.

Kefir is an interesting case. Research has measured high levels of B12 in kefir, with concentrations ranging from 412 to 640 micrograms per 100 mL, where the highest amount was found in kefir containing a B12-producing bacterial strain.¹⁶ These numbers are exceptionally high compared to plain milk, suggesting that certain kefir-specific bacteria actively synthesize B12 during fermentation. However, the specific strains used matter enormously, and not all kefir will deliver the same results.

Adding probiotic cultures before fermentation can also influence the B-vitamin profile of yogurt. Research found that probiotics increased the concentration of one form of vitamin B6 (pyridoxal) by about 14%, and milk from grass-based systems yielded fermented products with about 16% more folate (B9) than milk from indoor systems.¹⁷ The bottom line is that fermentation generally preserves most B vitamins and can boost some, particularly folate, while B12 may dip slightly unless the culture specifically produces it.

Milk’s Vitamins Compared to Alternatives

With the rise of plant-based milks, it is worth asking how cow’s milk stacks up. The short version: unfortified plant milks fall well short of cow’s milk in several key vitamins. If cow’s milk is replaced with non-fortified plant drinks, consumers risk deficiencies in calcium, zinc, iodine, and vitamins B2, B12, D, and A, a concern that is most acute for infants and toddlers who rely heavily on milk as a food source.¹⁸ While soy milk can approach cow’s milk in protein content, the biological value of its protein and the presence and bioavailability of vitamins and minerals generally do not match up.

A comparison of specific products found that folate and B12 were most notably decreased in goat’s milk and almond milk, while soy milk contained almost double the folate and B12 of cow’s milk, likely because of heavy fortification.¹⁹ This highlights a key distinction: many plant milks are fortified to close the gap, and the fortification levels vary wildly between brands. Checking the label matters more than assuming any category of plant milk is inherently equivalent or inferior.

Goat’s milk is sometimes marketed as nutritionally superior to cow’s milk, and the picture is genuinely mixed. One comparative analysis found goat milk had higher concentrations of several minerals and polyunsaturated fatty acids compared to cow’s milk, but lower levels of some important nutrients including calcium and zinc.²⁰ For B vitamins specifically, goat’s milk tends to be lower in folate and B12 than cow’s milk, which is a real consideration for people switching entirely from one to the other.

Bioavailability and the Milk Matrix

Knowing what vitamins are in milk is only half the story. What matters is how much of each vitamin your body can actually absorb, and milk’s food matrix appears to be unusually good at delivering its nutrients. The B12 in cow’s milk, bound to transcobalamin and casein, transfers efficiently to human carrier proteins during digestion. Whey proteins in milk have also been shown to stabilize B12: when tested in simulated gastric juice for two hours, one form of B12 was about 20% more stable in the presence of whey proteins than without them.²¹

For vitamin D, milk’s fat globules play a delivery role. Researchers investigating nanostructured lipid carriers made from milk fat globule membrane phospholipids and anhydrous milk fat found that vitamin D3 loaded into these carriers achieved about 88% bioaccessibility in simulated digestion, with good chemical stability.²² While that study was testing an engineered delivery system rather than plain milk, it underscores that the natural lipid structures in milk are effective vehicles for fat-soluble vitamins. Vitamin A, similarly anchored to the fat globule and its membrane, benefits from the same fat-mediated absorption pathway, which is one reason why drinking milk with a meal that contains some fat can help you get more out of the fat-soluble vitamins.

When Fortification Falls Short

Fortification programs transformed milk into a reliable vitamin D and vitamin A source at a population level, but the assumption that every carton hits the label’s target is shaky. The Ontario survey mentioned earlier found widespread inconsistency, with a majority of samples undershooting the intended vitamin D levels.⁹ Mixing and metering during processing, variations in the raw milk’s starting composition, and quality control differences across dairy plants all contribute. Regulatory oversight catches the worst offenders, but spot-checks have repeatedly shown that the vitamin content of retail milk is more variable than the neat numbers printed on the nutrition facts panel.

This matters most for people who rely on milk as a primary vitamin D source, which includes many children, older adults, and populations at higher latitudes with limited sun exposure. If you are counting on two or three glasses of milk per day to cover your vitamin D needs, the actual delivery might range from adequate to well below expectations depending on the specific carton. Combining milk with other vitamin D sources or occasional sun exposure provides a buffer against that variability.

Organic, Raw, and Specialty Milks

Raw milk advocates sometimes claim that unpasteurized milk is nutritionally superior because heat treatment destroys vitamins. The evidence on this is more nuanced than either side tends to acknowledge. Standard HTST pasteurization preserves B1, B2, B12, and E with no significant losses.¹¹ The vitamin differences between raw and standard pasteurized milk are too small to measure reliably in most studies. Where you start to see real losses is in higher-heat treatments like high pasteurization, which can cut B12 by nearly a quarter. The vitamin argument for raw milk over standard pasteurized milk is weak; the argument against UHT or high-pasteurization products has a bit more to it, at least for B12.

As for organic milk, its vitamin profile depends more on how the cows were fed than on the organic certification itself. Organic standards that require pasture access tend to produce milk with higher fat-soluble vitamin levels in summer months, mirroring the grass-fed effect seen in B-vitamin studies. But an organic cow fed mostly grain indoors is not going to produce meaningfully different milk from a conventional cow on a similar diet. The label alone does not tell you much about vitamin content without knowing the farming system behind it.

1
PubMed. Quantification of B-vitamins from different fresh milk samples using ultra-high performance liquid chromatography mass spectrometry/selected reaction monitoring methods
2
PubMed Central. Effect of Diet on the Vitamin B Profile of Bovine Milk-Based Protein Ingredients
3
PubMed. Transcobalamin derived from bovine milk stimulates apical uptake of vitamin B12 into human intestinal epithelial cells
4
PubMed. Vitamin B(12) and its binding proteins in milk from cow and buffalo in relation to bioavailability of B(12)
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PubMed. Vitamin A distribution among fat globule core, fat globule membrane, and serum fraction in milk
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7
PubMed Central. Vitamin D3 in High-Quality Cow Milk: An Italian Case Study
8
PubMed Central. Resurrection of vitamin D deficiency and rickets
9
PubMed. A survey of vitamin A and D contents of fortified fluid milk in Ontario
10
Proceedings of the Nutrition Society. Environmental and genetic factors influence the vitamin D content of cows’ milk
11
International Dairy Journal. Impact of thermal processing on micronutrients and physical stability of milk and cream at dairy production scale
12
PubMed. Comparison of milk oxidation by exposure to LED and fluorescent light
13
PubMed. Influence of milk fat, milk solids, and light intensity on the light stability of vitamin A and riboflavin in lowfat milk
14
PubMed. Interaction effect of LED color temperatures and light-protective additive packaging on photo-oxidation in milk displayed in retail dairy case
15
Journal of Dairy Science. Effect of Fermentation on B-Vitamin Content of Milk in Sweden
16
Food Bioscience. Determination of some physicochemical, microbiological, sensorial properties and vitamin B12 contents in kefirs by using biopreservative cultures
17
International Dairy Journal. B-vitamin concentrations in raw milk from dairy cows receiving diets differently by their forages and grassland contents and the resulting fermented milk products (cheese and yogurt)
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PubMed. Stability of vitamin B12 with the protection of whey proteins and their effects on the gut microbiome
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International Dairy Journal. Potential of milk fat globule membrane’s phospholipids and anhydrous milk fat based nanostructured lipid carriers for enhanced bioaccessibility of vitamin D3