Thousands of years ago, all milk was A2.
All the cows in the world only made A2 milk. Then, a few thousand years ago, there was a genetic change, a mutation that changed the milk that some cows were making into A1 milk. From a structural, molecular level, it's a very small change, but this small change may have a big impact on your health.
More likely than not, all the milk you drink has always been A1 milk. Cows producing A1 milk tend to have higher production, so most dairy farms use A1 cows. The milk they produce contains varying ratios of the two proteins, but it's usually mostly A1. Cows genetically tested and certified to be producers of A2 milk, get to label their milk as such. The potential negative effects of A1 milk are thought to be fairly wide reaching (autoimmunity, allergies, diabetes, and autism). How a small change can have such a big impact comes down to how the digestive system breaks down proteins.
So here's the nitty gritty.
Humans, goats, and sheep all make A2 milk, but in some breeds of cows there was a genetic mutation, like said above, thousands of years ago which changed the milk these cows made into A1 milk. The A1 vs A2 differ in the structure of a protein found in milk called beta-casein. A protein is a long string of amino acids, like beads of a necklace, all strung together. In A2 milk the 67th position in that chain is a proline amino acid, while in A1 milk, it was changed into a histadine. That seemingly insignificant difference changes a lot. Your digestive system is very good at cleaving protein strands at specific bonds, depending on the types of amino acids located there. The histadine in A1 beta-casein makes a weak link in the chain and an easy spot for the digestive juices to chop that protein down, producing a 7 amino acid long chain called beta-casomorphin 7 (BCM-7). BCM-7 is the culprit here and the compound responsible for the damage that A1 milk is thought to cause. If BCM-7 makes it across the intestinal membrane intact, it is able to bind to opioid receptors, trigger the immune system, reduce neurological antioxidant status, and is likely the cause of the allergic reactions many people experience when they drink milk.
There is fairly robust evidence for the damage caused by A1 milk and BCM-7. Correlational studies have connected consumption of A1 milk to autoimmune conditions, milk allergies, autism, type 1 diabetes and milk intolerance. Schizophrenic and autistic patients tend to have higher circulating blood levels of BCM-7. Anecdotally, in my practice, patients who cannot tolerate cow's milk, often do well on goat's milk (which is exclusively A2). BCM-7 is especially problematic in patients who have compromised gut integrity, aka: leaky gut. When leaky gut is present the BCM-7 is able to cross the intestinal membrane and enter the blood stream, where it can significantly impact health. This may explain why many people can spend most of their lives happily enjoying dairy with no problems then suddenly develop an intolerance (after the gut integrity has been compromised). This is also a big problem for infants, who start out with a permeable intestinal membrane. It has been long known that cow's milk is dangerous for infants, implicated in sudden infant death syndrome, asthma, allergies and type 1 diabetes. BCM-7 may be the culprit.
Despite relatively robust evidence of the harms from A1 milk, the medical community is far from in consensus on the subject. Studies on the negative effects of A1 milk are not always consistent, and lively critiques of the A1 vs A2 distinction have been published in various nutrition journals. Any time a large industrial interest exists in a health debate the evidence has to be evaluated with more caution and there are financial interests on both sides of the A1 vs A2 debate. The final word should always be your own experience. While I personally believe that there is sufficient evidence to chose A2 over A1 milk, I think the importance of that decision is dependent on your gut health, your immune system and your overall health status.
Here's the bottom line:
Milk can still be problematic for reasons besides BCM-7. It can be the lactose, the whey, the casein, or various other proteins that you are reacting to. If you do fine with goat products, but can't do cow's milk, then you are more likely to do well with A2 milk. If you are suffering from mild symptoms like nasal congestion or skin reactions when you consume milk then, by all means, try A2 milk. If you are suffering from a severe autoimmune condition and you have eliminated milk from your diet because it impacts how you feel, it would be safest to continue to abstain from consuming dairy. Why? Well, when there is one immune activating agent present, the compounds around it are also more likely to develop immune recognition. In other words, it's guilt by association. While A2 milk may not have BCM-7, it still has whey, and other protein fragments, that your body may have become sensitive to while reacting to BCM-7. In your case, the stakes are likely too high.
Want more information?
"The Devil in the Milk", written by Keith Woodford in 2007
This Mother Jones Article
Here's a good review in the European Journal of Clinical Nutrition countering many of the arguments from the A2 camp.
I'm Kieran, clinician and founder at The Parani Clinic. I'm an acupuncturist, herbalist, and functional medicine practitioner for the past 10 years. I have a deep curiosity in health, biology, culture, medicine, history, and a healthy obsession with the pursuit of the perfect state of health.