37% of breast cancer cases can be attributed to exposure to bovine leukemia virus.
Breast cancer incidence continues to increase worldwide. In the United States, this represented a 40% increase in incidence by the beginning of this century. Currently, the main approach to preventing death is early detection and treatment. That’s important, but why not focus more on primary prevention, which protects people from risk factors so they don’t develop breast cancer at all?
“Overall, it is estimated that 20% of human cancers are infectious.” Viruses can cause cancer by turning on oncogenes or turning off tumor suppressor genes, but they can also contribute to tumorigenesis simply by causing chronic inflammation. Oncogenic viruses are now considered “the leading hypothesis for the direct cause of human breast cancer.” How did we get here?
It all started about 40 years ago, when a professor of virology at the University of California, Berkeley, learned how mammary tumor viruses were discovered in mice. When the scientists swapped pups from mothers with high rates of breast cancer with those from strains of mice with low rates of breast cancer, they found that the cancer rates in the offspring were not biological, but matched those of their adoptive mothers, and were not genetic. “I thought that humans were raised on cows,” the professor said.
Bovine leukemia virus (BLV) had just been identified as a bovine virus that causes cancer. At the time, the infection rate among dairy cows in the United States was only about 10%; today it is nearly half that rate. Initially, 66% of the herd was affected. And based on milk testing results for the virus, nearly 80% were positive, compared to 100% in herds from large industrial farms. And now more than 94% of the U.S. dairy herd is affected, continuing the historic trend of persistent proliferation of BLV within the U.S. dairy herd.
It has long been known that people in countries that consume the most milk have the highest incidence of breast cancer. But as you can see below and at 2:32 in my video “Bovine Leukemia Virus as a Cause of Breast Cancer,” the association between dairy intake and breast cancer incidence is not just at the national level.Women who are lactose intolerant and consume less dairy also appear to have a reduced risk of breast cancer. Milk contains many things that can contribute to cancer risk, including saturated fat and the presence of carcinogenic growth hormones such as IGF-1.
Yes, we know that bovine leukemia virus is present in beef and dairy products. About half of the milk and meat samples tested positive for the virus. In fact, we can sample viruses directly in the air, on surfaces, and in the milk itself in dairy farms. Most milk is pasteurized, but many dairy products, such as raw aged cheese, are not. And who hasn’t had a burger with a pink center at some point in their life?
Yes, there is evidence that people are being exposed to the virus. Yes, there is evidence that people are actively infected with the virus. However, it wasn’t until 2015 that we discovered that infection rates were highest in cancerous breast tissue, as seen below and at 3:30 in my video.
So much so that 37% of breast cancer cases can be attributed to exposure to bovine leukemia virus.
That was enough to create a series of videos about the role the virus plays in breast cancer and how the meat and dairy industries responded to the news. What’s the latest update? We’ll talk about it next.
doctor’s note
You may remember that I previously discussed “The Role of Bovine Leukemia in Breast Cancer and Industry’s Response to Bovine Leukemia Virus in Breast Cancer.”
Stay tuned for the next video, “Breast Cancer and Bovine Leukemia Virus in Meat and Dairy.”
