Does casein -- the main protein in milk -- cause cancer? No, that's not true: casein is not listed as a carcinogen by the International Agency for Research on Cancer or the U.S. National Toxicology Program.
The claim originated from a video (archived here) published by the Dr. McDougall Health and Medical Center YouTube channel on February 29, 2016, under the title "
This is what the video looked like on YouTube at the time of writing:
At 2:43 in the 9-minute, 24-second video, Campbell says:
Casein is the most relevant chemical carcinogen ever identified, make no mistake about it ..."
Casein is not identified as a carcinogen by the International Agency for Research on Cancer (IARC) nor the U.S. National Toxicology Program (NTP). According to cancer.org, the two function independently as registries of known cancer agents.
Campbell describes in the video how he came to his conclusion after doing an experiment on rats. The experiment was to see how different levels of protein would affect a living organism. In his study, there were two groups of rats, one was given a diet of low protein (casein) and the other, a diet of high protein. The conclusion that Campbell came to at the end of the experiment was that the rats with the low-protein diet did not develop cancer and were healthy, while the rats with the high-protein diet developed cancer and were unhealthy.
What Campbell failed to mention in his non-peer reviewed book, "The China Study" was that the rats that developed cancer after eating casein may have already had cancer cells present in their bodies.
Other research calls into question his conclusion casein should be classified a carcinogen. A peer-reviewed article in the World Journal of Men's health describes a study that found that casein can increase the growth of prostate cancer cells. In this study, casein did not affect lung cancer cells, stomach cancer cells, breast cancer cells, immortalized human embryonic cancer cells, and immortalized normal prostate cells. The study was cited 24 times, while Campbell's study has only been cited by himself (twice). Citations are considered a measure of acceptance of findings by the scientific community.
Further research showed that the rats and mice tested already had cancer cells present. The articles based on Campbell's studies, make it clear casein was being given to rats and mice with cancer. In his two scientific papers published in the 1990s, the conclusion found no evidence that a high diet of casein resulted in cancer. Instead, the mice had already been exposed to risk factors that have a high chance of starting the growth of liver cancer cells (aflatoxin and hepatitis B virus) before getting introduced to a high casein diet.
What Campbell found casein could do was influence tumor growth and incidence in mice that had already been given the risk factors for liver cancer, but there is no evidence in his studies that suggest cancer growth began in mice that were not already injected with the risk factors for liver cancer.
The World Cancer Research Fund and the American Institute for Cancer Research started a Continuous Update Project (CUP) tracking milk studies. In 2018, the CUP Panel concluded that, "the evidence was generally consistent for dairy products, milk, cheese, and dietary calcium, and showed a decrease risk of colorectal cancer with higher consumption."
Lead Stories reached out to Dr. Scott Rankin PhD, a professor and chair of the University of Wisconsin-Madison's Department of Food Science. Dr. Rankin described himself as a chemist, with experience in dairy foods.
When asked what advice he would give to people who are afraid animal protein and dairy will give them cancer, Rankin responded:
We take a lot of steps to avoid the growth of that mold and cancer causing agents to be present in our food. For instance, the beer industry does that a lot with grains they use for beer because they use a lot of grains and if it's moldy, it'll have a certain amount of what's called aflatoxins, so they take means to control it.
Aflatoxins are potent carcinogens, according to the World Health Organization (WHO), and may affect many organ systems, including the liver and kidneys. The WHO goes on to say, "...[aflatoxins] cause liver cancer, and have been linked to other types of cancer...the potency of aflatoxin to cause liver cancer is significantly enhanced in the presence of infection with hepatitis B virus (HBV)".
All the experiments that milk has displayed over these eons that we've been evaluating it, continue to suggest that it's a very healthy part of a balanced diet. So I wouldn't have any hesitancy endorsing milk to anybody, including my own family.