Cow Cancer Virus Implicated in Breast Cancer

Up to 20 percent of all cancers in general are linked to infections, particularly viruses, and the list of potentially carcinogenic infectious agents is growing. It would be great if we could find a virus that contributed to breast cancer risk, because then we might have new ways to prevent and treat it. Currently, the dietary link between breast cancer and consumption of meat and dairy is considered a saturated fat effect, but there is a cancer-causing bovine virus that infects the mammary gland cells of cows. The infectious virus is then released into the milk supply. Since most U.S. dairy herds are infected, scientists posit that Americans are often exposed to this bovine leukemia virus (BLV), which I discuss in my video The Role of Bovine Leukemia Virus in Breast Cancer.

We didn’t have proof of this until 2003, 34 years after the virus was first identified. Early on, our best available tests failed to find antibodies to BLV in human blood. When our immune system is exposed to a virus, it creates antibodies to attack it. No antibodies, no exposure. “This led to the prevailing opinion that…the virus is not a public health hazard.” Though those tests “were state of the art at that time, they are extremely insensitive compared to more modern techniques.” As a result, researchers decided to re-examine the issue now that we have better tests. They took blood from about 250 people simply to address the question: “Do any humans have antibodies to BLV?” The answer? Yes, 191 of them did––74 percent. That shouldn’t have come as a surprise, however: By then, nearly 90 percent of American dairy herds were infected, and, according to the latest national survey, 100 percent of the big factory dairy farms were infected, as determined by testing the milk coming from those operations. Given this, why isn’t there an epidemic of cancer of the udder? Dairy cattle are slaughtered so young that there isn’t a lot of time for them to develop gross tumors, but that’s how most women may be getting infected. Although pasteurization should knock out the virus, who hasn’t eaten a rare, pink-in-the-middle burger at some point?

The bottom line is that the “long-held assumption that BLV is not a public health hazard…is no longer tenable…” This whole field of investigation needs to be reopened, with the next step determining whether humans are actually infected. “The presence of antibodies to particular viruses in human sera is generally interpreted as an indicator of a present or past infection with the virus.” But, theoretically, we might have developed antibodies to the dead viruses we ate, viruses that had been killed by cooking or pasteurization. Just because three-quarters of us have been exposed doesn’t mean we were actively infected by the virus.

How do we prove this? We would need to find the retrovirus actively stitched into our own DNA. Well, millions of women have had breast surgery, so why not just look at the tissue? Researchers finally did just that and published their findings in the Centers for Disease Control and Protection’s emerging infectious diseases journal: Forty-four percent of samples tested positive for BLV, proving for the first time that humans can be infected with bovine leukemia virus. The final step? Determine whether the virus is actually contributing to disease. In other words, are the bovine leukemia viruses we’re finding in human breast tissue cancer-causing or just “harmless passengers”?

One way to make that determination is to see whether the virus is more often present in those with breast cancer. No one had ever looked for the virus in breast tissue from people with cancer…until now. The “[p]resence of BLV-DNA in breast tissues was strongly associated with diagnosed and histologically confirmed breast cancer…” As many as 37 percent of human breast cancer cases may be attributable to exposure to bovine leukemia virus.


For some historical background leading up to these shocking findings, see my video Is Bovine Leukemia Virus in Milk Infectious?.

I couldn’t wait to read the meat and dairy industry journals to see how they’d try to spin this. Find out what I discovered in my final video in this series Industry Response to Bovine Leukemia Virus in Breast Cancer.

In health,
Michael Greger, M.D.

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

Concerns About Bone Broth

There are toxicological issues associated with production and processing of meat, such as the presence of various toxic contaminants—from dioxins and PCBs to cooked meat carcinogens. Carcinogenesis, the development of cancer, may be the main concern, but there are a number of other toxic responses connected with the consumption of meat products. Lead, for example, can be toxic to the nerves, gastrointestinal tract, bone marrow, and kidneys.

Where is lead found in the food supply? In general terms, the highest levels of lead, as well as arsenic and mercury, are found in fish. Sardines have the most arsenic, but tuna may have sardines beat when it comes to mercury and lead.

The problem is that “fish-consumption advisories related to human health protection do not consider the fish by-products fed to farmed animals,” like farmed fish. If some tilapia are fed tuna by-products, they could bioaccumulate heavy metals and pass them onto us when we eat them. Researchers found the highest levels in frozen sole fillets, averaging above the legal limit for lead.

Lead exposure has been shown to have adverse effects on nearly every organ system in the body. Symptoms of chronic exposure range from memory loss and constipation to impotence and depression. These symptoms present after pretty hefty exposure, though. However, we now know that “[b]lood lead levels in the range currently considered acceptable are associated with increased prevalence of gout and hyperuricemia” (elevated levels of uric acid in the blood). According to the Centers for Disease Control and the World Health Organization, a blood lead level needs to be less than 25 micrograms per deciliter to be “non-elevated.” You’d assume that at values under 25, there’d be no relationship with health outcomes, but even throughout this “acceptable” range, lower lead means lower uric acid levels and lower gout risk. So, even blood lead levels 20 times below the acceptable level can be associated with increased prevalence of gout. “These data suggest that there is no such thing as a ‘safe’ level of exposure to lead.” 

Once lead gets into the body, it tends to stay in the body. It builds up in the bones such that it may take 30 years just to get rid of half. The best strategy? Don’t get exposed in the first place.

If lead builds up in bones, though, what about boiling bones for broth? As I discuss in my video Lead Contamination in Bone Broth, we know bones sequester lead, which can then leach from the bones. So, researchers suggested that “the bones of farmyard animals will sequester lead, some of which will then be released into broth during its preparation.” Who eats bone broth? Bone broth consumption is encouraged by many advocates of the paleo diet. Online, you can learn all about purported “benefits” of bone broth, but what they don’t tend to mention is the theoretical risk of lead contamination—or at least it was theoretical until now. Broth made from chicken bones was to have markedly high lead concentrations, up to a ten-fold increase in lead. Researchers concluded, “In view of the dangers of lead consumption to the human body, we recommend that doctors and nutritionists take the risk of lead contamination into consideration when advising patients about bone broth diets.”

But what if you only use bones from organic, free-range chickens? They did use only bones from organic, free-range chickens.


For more on the paleo diet, see:

Other products contaminated with lead include Ayurvedic supplements, protein powders, wild animals shot with lead ammunition, dairy products, and tea from China:

In health,
Michael Greger, M.D.

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

Does Smoking Really Protect Against Parkinson’s Disease?

The Centers for Disease Control and Prevention recently celebrated the 50-year anniversary of the landmark 1964 Surgeon General’s report on smoking, considered one of the great public health achievements of our time and the first of 30 other such reports from the Surgeon General on smoking. Internal tobacco industry memos, which you can see in my Is Something in Tobacco Protective Against Parkinson’s Disease? video, document their response. Major criticisms of the report include a “[c]avalier treatment of costs of smoking”: The Surgeon General argued that smoking costs the United States billions, but the tobacco industry noted that “smoking saves the country money by increasing the number of people dying soon after retirement,” so we don’t have to pay for Social Security, Medicare, and the like. In fact, the industry argued, if we were truly patriotic, maybe we should encourage smoking to help balance the budget!

The tobacco industry also criticized the Surgeon General for a “[l]ack of balance regarding benefits of smoking,” asserting that “[o]ne has to search pretty hard to find any concession anywhere in the Report that smoking is not all bad.” This is something the tobacco industry liked to bring up when testifying before Congress, saying that health benefits include “the feeling of well-being, satisfaction, and happiness and everything else.” But beyond just all the happiness the Surgeon General was trying to extinguish, he failed to even mention that smokers appear protected against Parkinson’s disease.

“Quite unexpectedly…[m]ore than 50 studies over the last half century consistently demonstrated reduced prevalence of Parkinson’s disease among smokers compared with never-smokers.” Now there are more than five dozen studies.

But smokers are probably dying before they even have a chance to get Parkinson’s, so is that the explanation? No, that didn’t seem to be it. Researchers found a protective effect at all ages. Maybe it’s because smokers tend to be coffee drinkers, and we know coffee consumption alone appears protective. But, no. The protective effect of smoking remained even after carefully controlling for coffee intake. Well, maybe we inherit some propensity to not smoke and to get Parkinson’s. If only we could clone someone to have the same DNA. We can! They’re called identical twins. And still, the relationship remained, suggesting “a true biologic protective effect of cigarette smoking.”

Not so fast. Maybe finding unusually low rates of Parkinson’s among smokers is an example of reverse causation. That is, maybe smoking doesn’t protect against Parkinson’s—maybe Parkinson’s protects against smoking. Could there be something about a Parkinson’s brain that makes it easier to quit? Or perhaps failure to develop a smoking habit in the first place is an early manifestation of the disease.

To put that to the test, researchers studied children exposed to their parents’ smoke. If they grew up to have less Parkinson’s, that would confirm the protective link—and indeed they did. So, smoking really does seem to be protective against Parkinson’s disease, but who cares? How does that help us? “More than 20 million Americans have died as a result of smoking since the first Surgeon General’s report…” Even if we didn’t care about dying from lung cancer and emphysema, even if we only cared about our brain, we still wouldn’t smoke because smoking is a significant risk factor for having a stroke, as well.


Is there a way we could get the benefits of smoking without the risks through our diet? I discuss this in my Peppers and Parkinson’s: The Benefits of Smoking Without the Risks? video.

Other Parkinson’s videos include Preventing Parkinson’s Disease with Diet and Treating Parkinson’s Disease with Diet.

Diet may play a role in other movement disorders. For example:

Surprised about the potential benefits of coffee? See:

In health,
Michael Greger, M.D.

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