Is the Casein in A2 Milk Healthier?

The casomorphins—breakdown products of casein, a milk protein, with opiate-like activity—in bovine milk appears to have opposite effects than those from human breast milk on infant development, but what about A2 cow’s milk?

“One of the main sources of opioid peptides”—that is, protein fragments with opiate-like activity—”in the autism patients diet are dairy products.” As I discuss in my video Does A2 Milk Carry Less Autism Risk?, casein, the main dairy protein, breaks down into casomorphins, which “are considered to be factors involved in etiology [the cause] and exacerbation of symptoms in food allergy and atopic dermatitis [eczema], diabetes, schizophrenia, postpartum psychoses, sudden infant death syndrome (SIDS), and autism.” According to this opioid-excess idea, the development of autism includes a genetic predisposition and early exposure to some kind of environmental stressors that affect the gut, which may cause more of these casomorphins to leak into the blood and then the brain, where they may play a role in the development of autism. You don’t know, though, until you put it to the test.

First of all, do these bovine casomorphins form in the human digestive tract when we drink milk? Researchers decided to insert tubes down into subjects’ intestines to find out and, indeed, “considerable amounts” of casomorphin were found. Do they get absorbed into the bloodstream, though? Yes, apparently so, but the study was on infants who naturally have leakier guts. Do fully intact casein protein fragments make it into the bloodstream after infancy? Yes, as you can see at 1:24 in my video. In fact, they can get into the bloodstream even into adulthood, elevating levels in the blood for at least eight hours after consumption.

And, those with autism may have an especially leaky gut at significantly higher risk for abnormally high intestinal permeability, which may explain why the vast majority of children with autism may have antibodies in their blood to wheat and dairy proteins, compared to a small minority of children without autism, as you can see at 1:44 in my video. And, based on allergy studies, even if infants are strictly breastfed, they may still be exposed to bits of bovine milk proteins if their mothers drink milk, as the bovine protein fragments can get into the mother’s blood, then her breast, and then into her baby’s body. But, do the cow proteins also get into the baby’s brain?

Those with autism are more likely to suffer from leaky gut, but the “opioid excess theory” depends on casomorphins not only getting into the bloodstream, but also up into the central nervous system, which includes the brain. There’s something called the blood-brain barrier, which helps cordon off the brain, but when you examine the brain tissues of those with autism, their blood-brain barrier seems leakier, too. Indeed, evidence for the presence of casomorphins within the brains of infants has since been confirmed. If you think about it, it just makes sense. Presumably, the whole point of casomorphin opioids is to affect the brains of babies so they crave the milk and cry out for the milk, strengthening the mother-infant bond and, similarly, the cow-calf bond. That’s what’s supposed to happen. It’s normal and natural. In that case, why are casomorphins associated with disease? Well, such a bond between a human mother and her human infant is natural, whereas one between a cow and a baby or a human mom and a calf isn’t.

As you can see at 3:24 in my video, human infants with evidence of higher baseline levels of bovine casomorphins in their blood seem more likely to be suffering from psychomotor delay, which is a measure of muscle, language, and mental function development, but the reverse was found for human infant exposure to human casomorphins, meaning human casomorphins appeared to be beneficial in humans. Just as bovine casomorphin levels in human babies’ blood appear to rise after feeding them cow’s milk formula, human casomorphin levels rise in babies after breastfeeding, which is what’s supposed to happen. “The greatest basal irHCM [baseline human casomorphins] was revealed in breastfed infants with normal psychomotor development and muscle tone. In contrast, elevated basal irBCM [baseline bovine casomorphins] was found in [cow’s milk] formula-fed infants showing delay in psychomotor development,” as well as, more rigid, muscle tone.

“The explanation of opposite effects of human and bovine CM [casomorphins] on infants’ psychomotor development and muscle tone probably lay in their species-specificity.” Cow’s milk is good for calves, and  breastmilk is good for babies. Indeed, the structures of bovine casein and human casein are dramatically different, and the bovine and human casomorphins themselves are different molecules, differing by two amino acids, which results in greatly different potencies. Compared to human casomorphin, bovine casomorphin “is highly potent and similar to morphine in its effects.”

A difference of two amino acids may not seem like a lot, but casomorphins are only seven amino acids long. This difference of about 30 percent “likely defines a difference in their biological properties. Both human and bovine CMs [casomorphins]…interact with opioid and serotonin receptors which are known to be of great importance for CNS [central nervous system, including the brain] maturation,” but cow casomorphin binds more tightly to these receptors, so it has more of an effect. As such, this can help explain not only why breast is best, but also why the psychomotor delay linked with higher bovine casomorphin levels in the blood supports this concept that cow casomorphins may play a role in a disease such as autism.

This is why bovine casomorphins have been called “the devil in the milk,” but are they formed from all cow’s milk? What about “A2” milk? The A2 Corporation points out there are different variants of casein: Some cows produce milk with a kind of casein dubbed A1, while other cows produce milk with A2 casein. A2 differs from A1 by only single amino acid, but one that is strategically located such that A1 casein breaks down into casomorphin, which acts like morphine and is “implicated in digestive, immune and brain development changes.” Supposedly, A2 milk does not do the same. As you can see at 6:18 in my video, if you put A1 milk in a test tube with some digestive enzymes, the A1 casein breaks down into casomorphin. But, because of that one amino acid difference, the A2 casein breaks down at a different spot and no casomorphin is formed.

That study, however, used digestive enzymes from pigs or cows, which are cheaper and easier to buy for laboratory experiments. Human digestive juices are different, so what happens in a pig’s stomach or a cow’s stomach may not necessarily be what happens in the human digestive tract. 

When the A1 versus A2 breakdown experiment was finally performed with human enzymes, what was discovered? Human stomach and intestinal juices were collected, and the devil was found in both. The opioid casomorphin was produced from both A1 milk and A2 milk. So, A2 milk may be better for pigs or cow, but not necessarily for humans. 

This article discusses the second video in a six-part series on the role of gluten- and dairy-free diets in the treatment of autism. If you missed the first video, see Autism and Casein from Cow’s Milk. 


Stay tuned for: 

Keep abreast of all of my videos on autism here.

I previously touched on A1 vs. A2 milk in Does Casein in Milk Trigger Type 1 Diabetes? and Does Bovine Insulin in Milk Trigger Type 1 Diabetes?.

In health, 

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Do Casomorphins from Cow’s Milk Contribute to Autism?

Casomorphins—breakdown products of casein, a milk protein, with opiate-like activity—may help explain why autism symptoms sometimes improve with a dairy-free diet.

In my last video series on autism and diet, I talked about the benefits of broccoli sprouts, but the most commonly studied nutritional and dietary interventions for autism and diet involve variations of gluten-free and casein-free diets. Why?

In the 1980s, a team of respected Norwegian researchers reported a peculiar finding. They were comparing the urine of children with and without autism in the hopes of teasing out any differences that could lead to hints to the cause of autism. As you can see at 0:42 in my video Autism and Casein from Cow’s Milk, a urine profile shows spikes for each of the various components. Normally, the urine’s peptides region is pretty quiet. Peptides are like small pieces of proteins, and, normally, we shouldn’t be peeing out much protein. But, in the urine profiles from children with autism, there were all sorts of peptide spikes.

This difference raised a question: “Can the pathophysiology”—that is, the dysfunction—“of autism be explained by the nature of the discovered urine peptides?” But, first: “Where do the peptides come from?” They didn’t know, but there was a clue: Most of the parents of kids with autism reported that their children’s disorder got worse when they were exposed to cow’s milk. In fact, two proteins—gluten, a protein in wheat, and casein, a protein in milk—break down not only into peptides, but also into exorphins.

Exorphins, opioid peptides derived from food proteins, “are called exorphins because of their exogenous [that is, from outside of the body] origin and morphine-like activity,” as opposed to endorphins, which are morphine-like compounds we produce inside our bodies. Perhaps some of these food peptides represent a new class of hormones?

Well, is that what the kids were peeing out? Apparently so, as some of those peptides had opioid activity. Maybe the researchers were on to something. 

Two types of opioids have been found in milk: casomorphins, “in view of their morphine-like activity and their origin—they represent fragments of the milk protein β-casein,” and the actual opiate, morphine. There appears to be actual morphine in milk. This can’t just be a coincidence. “It is difficult to believe that these, or other types of opioids found in the milk, can be devoid of physiological, or nutritional, significance.” If you think about it, it makes total sense. “Morphine and the opioid peptides may also have an important role in the mother-infant bonding mechanism, because the infants may be ‘addicted’ to their own mother’s milk.” But, what about the milk of another species?

“Human milk is markedly different from that of other mammalian species” in that it has the lowest casein content. Further, human casein is a markedly different protein in terms of its sequence of amino-acid building blocks.

As you can see at 3:40 in my video, human breastmilk has about 15 times less casein than cow’s milk and differs in its amino acid sequence by about half, so it breaks down into peptides differently. “Twenty-one peptides were identified from cow casein proteins,” including multiple casomorphins, compared to only five active peptides identified in human milk and just one casomorphin. What’s more, “those [casomorphins] from bovine casein are more potent than β-casomorphins from human milk.” At 4:08 in my video, you can see a graph of opioid activity, where lower means more potent. Bovine casomorphin was shown to be significantly more potent than the weak opioid peptide from gluten, a substance more comparable to the casomorphin from human breastmilk.

Indeed, when you expose human nerve tissue to bovine casomorphin, it acts more like morphine than the casomorphin from human breastmilk in terms of epigenetic changes, changes in gene expression, not only providing “a molecular rationale for the recommendation of breastfeeding vs. [cows’ milk] formula feeding,” but also providing a possible explanation why “casein-free, gluten-free diets have been reported to mitigate some of the inflammatory gastrointestinal and behavioral traits associated with autism…” 

“What is good for the goose may be good for the gander, but what is good for the cow could be harmful to the human.” 


This article discusses the first video in a series on the role of gluten- and dairy-free diets in the treatment of autism. Stay tuned for the other five videos in this six-part series: 

My previous series on autism explored the amazing story of broccoli sprouts put to the test for the treatment of autistic boys. See: 

Keep abreast of all of my videos on autism here.

You may also be interested in these videos on milk and child and infant health:

In health, 

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Lead in Seafood and Wild Game

Most hunters may not be aware of the health risks related to consuming meat from animals shot with lead ammunition.

I’m often asked in lectures whether microwaves are safe. Not if you drop them on your foot! But, otherwise, it matters what you’re putting in them—sweet potatoes and broccoli, or hot pockets and pop tarts? Similarly, when I was exploring the safety of hot sauces in my video Flashback Friday: Lead Contamination in Hot Sauces, given their potential for lead contamination, I had a similar reaction: It matters what you’re putting them on.

When I think about toxic pollutants, the first thing I think of is the aquatic food chain. We know, for example, that giving people a seven-ounce portion of a fish high in mercury, like tuna or swordfish, just once a week, which is about a can and a half of tuna a week, can quadruple mercury levels in the blood within a few months. What about lead?

A dietary intervention with not one but five portions a week significantly increased blood concentrations of toxic metals, including lead. Even though “the background intake of lead was already disturbingly high,” the seafood intake “increased the intake of lead by approximately 25%.” From a public health perspective, it is important to recognize that the amount of seafood researchers used in the study “far exceed[ed] the intake of most populations.”

Lead can also bioaccumulate in other animals, but half of our dietary exposure to lead probably comes from plant foods. Animals shot with lead ammunition, though, may present a special case. I explore this in my video Lead Contamination in Fish and Game.

We know lead is toxic and banned from most household items in developed countries—except for lead ammunition, which “is now likely the greatest, largely unregulated source of lead that is knowingly discharged into the environment in the USA.” But, it is not just discharged into the environment. It’s also discharged into the meat itself. “People generally reject the idea of injecting toxic substances into food, except when it involves hunting wild game.”

Eighty percent of ground venison was found to contain lead, which isn’t surprising given the hundreds of metal fragments that end up in deer carcasses after being shot with standard lead-based rifle bullets—“an impossible number of fragments to pick out by hand, especially because some of these fragments are microscopic.”

As you can see at 2:23 in my video, researchers have shown using x-rays that during penetration, expanding lead core bullets typically release hundreds or thousands of fragments—or even millions or tens of millions of microscopic lead particles per gram. So, one serving could have a billion particles, though they are nanoparticles, extremely tiny, about the size of viruses. 

The only good lead, though, is no lead. Even very low levels of lead exposure can result in brain and nerve damage, yet most hunters may not be aware of health risks related to consuming meat from animals killed with lead ammunition.

Children may be at risk of losing IQ points, which could reduce their future prospects. “Often when I explain to hunters the risk associated with lead exposure, especially when considering their children,” writes a physicians, “their response is, ‘I have been hunting for years and I am fine.’ My response to them is, “but just imagine how smart you could have been.”

Bone broth is another issue, which I cover in Lead Contamination in Bone Broth.


I recently did a deep dive into lead if you’re interested in a comprehensive overview:

In health, 

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: