Cow Milk and Human Breast Cancer

September 28, 2015

Cow Milk and Breast Cancer 

 Reference: Plos1 Sept 2015 

 Sept 28, 2015 

 Bovine leukemia virus (BLV) is widespread in cows. When you test milk from large dairy farms (where all the milk is mixed together) you get 100% of milk samples containing the virus. When you test milk from farms with 100 cows or less, you will find that 83% of samples have the virus.   It should be cleared with pasteurizing.   Only 5% of cows infected with it show any evidence of illness, so it’s not exactly a dangerous virus for cows.   

Up till now, it was believed that the virus is not transmitted to humans. So when the authors of this study from Berkeley looked at samples of 239 cancers of the breast, they found that 59% had BLV antibodies.   Women with premalignant changes had the virus detected 38% of the time and breast samples from women with no cancer only showed the virus 28% of the time.   That makes a gradated level of risk that adds to the plausibility of an association. Considering that most cancers take 20-30 years to emerge, it would not be surprising that 29% of controls with no evidence of cancer showed signs of cancer, only lifetime observation will prove whether they develop cancer over a lifetime. 

 How does the virus get from cows to humans? That is not known. Pasteurizing should work – but on occasion may not. Raw milk would certainly be one means. Raw hamburger might also be. The virus might be in humans for generations, being passed on in humans. There is currently no known route of transmission. But there it is.  And populations that drink milk have much more breast cancer than those who don’t. 

 The means by which the BLV virus causes cancer has been studied and is fairly well understood. Just like the HPV virus, which is also a “retrovirus”, it inserts itself into the DNA of the cell and breaks up the ability of the cell to repair its own DNA.   Mutations begin to occur and over a lifetime gradually accumulate. In the right environment, the emergence of a cancer is possible. 

 Does this prove that the virus causes cancer? No, no! Don’t jump to that just yet. The women in this study might be very different populations. The authors took breast tissue from women who already had cancer and women with reduction mammoplasties. They might be very different populations. This association, though, is now stronger than any other for risk of breast cancer other than age and Brca1 gene. (Diabetes, non-human hormone therapy, smoking, etc). That gives it the possibility of being a screening function for breast cancer risk that might be more sensitive for future risk than what we currently employ. 

In cows with a persistent high white count, only 1 in 50,000 white cells show evidence of the virus, so it’s not exactly an easy thing to screen for, but then again, nothing is at first until you figure out methods by which to improve. And we do have retroviral drugs now for HIV. Might they work on this virus? 

 WWW. What will work for me?   Well, I’m not doing anything at the moment.   It does make me a bit more cautious about raw milk. I might cook my hamburger a bit more done, but I should be doing that anyway considering e. coli and company.   But this is a tidbit of information I want to keep knowing, and being aware of.   

 Pop Quiz

  1. Cow leukemia virus causes breast cancer. T or F.            Answer:   Whoa Nellie. Not so fast. But it may be part of the picture. Not proven yet.
  1. The association of BLV and breast cancer is stronger than most risk factors, like family history which is only 2% of risk. T or F                       Answer:   Perfect.
  1. Altered human hormones represent a greater risk for breast cancer than this virus. T or F. Answer:  Yup
  1. It takes 20-30 years for a cancer to emerge from its first mutation. T or F              Answer:   True
  2.  Very likely I should stop drinking milk because of this finding.  T or F               Answer. Well, probably not. This is still just in the form of information. Hang in there.  But it might color your opinion of milk just a bit.  
  3. We have good tests to screen for BLV. T or F                        Answer:   False. Nothing yet. This is all research material.