Got Dairy?

Welcome to Nutrition Facts.  I’m your host, Dr. Michael Greger, and I’m here to ask you, what is the most important decision you’ll make today, is it how you’ll get to work, who you’ll set up a meeting with, what friend you’ll call for lunch?  Well, as it turns out, probably the most important decision you’ll make today is what to eat.  What we eat on a day-to-day basis is the number one determinant of our health and longevity—literally.  Most premature deaths in the United States are preventable and related to nutrition.  So, we’re going to explore some smart nutrition choices based, naturally, on facts.  Here, we refer to the science, the research, the available data published in the peer-reviewed medical literature right now.  That’s why I wrote my book, “How Not to Die”, and why I created my nonprofit site NutritionFacts.org and, now, this podcast.

Today, we look at the nutritional value of dairy products.  The first U.S. dietary guidelines were issued in 1980 and recommended limits on saturated fat intake (found primarily in dairy), was fought tooth and nail by the dairy industry.  

But, that’s not the only concerning component.  “Fear of consumer reaction” led the U.S. dairy industry to try to suppress the discovery in retail milk of live paratuberculosis bacteria, a pathogen linked to a number of autoimmune diseases, including type 1 diabetes.

Type 1 diabetes “arises following the autoimmune destruction” of the insulin-producing cells of the pancreas.  It’s “often diagnosed in children and adolescents,” who usually present with “a classic trio of symptoms”—excessive thirst, hunger, and urination—as their blood sugars spike and, they need to go on insulin for the rest of their lives, since their own immune system attacked and destroyed their own ability to produce it.  What would cause our body to do such a thing?   Whatever it is, it’s on the rise around the world, starting after World War II.  “Understanding why and howthe current pandemic of childhood diabetes” was produced “would be an important step toward reversing it.”  A plausible guess is that of so-called “molecular mimicry,” whereby a foreign antibody generator (like a bacterium or virus) “provokes an immune response, which cross-reacts with a similar”-looking protein on our own pancreas—such that when we attack the bug, our own organ gets caught in the crossfire. 

Okay, so, what pancreatic proteins are type 1 diabetics self-attacking?  In the ‘80s, a protein was identified, which, in the ‘90s, we realized looked an awful lot like a certain mycobacterial protein.  Mycobacteria are a family of bacteria that cause diseases like tuberculosis and leprosy.  And, all newly diagnosed type 1 diabetic children were found to have immune responses to this mycobacterial protein but, that didn’t make any sense.  I mean, type 1 diabetes is going up in the industrialized world, whereas, you know, TB and leprosy rates are going down.  Well, there is one mycobacterial infection in livestock that’s shot up with the industrialization and globalization of animal agriculture—called paratuberculosis—which causes Johne’s disease in animals, now recognized as a global problem for the livestock industry.

Huh, weren’t there like a dozen studies suggesting that exposure to cow’s milk may be “an important determinant of subsequent type 1 diabetes” in childhood?  Putting two and two together, an idea was put forward in 2006.  Could Mycobacterium paratuberculosis be a “trigger” for type 1 diabetes?  It was a compelling enough idea that researchers decided to put it to the test.

They attempted to test the association of MAP, the full name for the bug—Mycobacterium avium paratuberculosis—with type 1 diabetes, by testing diabetics for the presence of the bacteria in their blood.  And, lo and behold, most of the diabetic patients were found positive for the bug, compared to only a minority of the healthy control subjects.  This evidence of MAP bacteria in the blood of patients with type 1 diabetes “might provide an important foundation in establishing an infectious” cause for type 1 diabetes.  “These results might have implications for countries that have the greatest livestock populations and a high incidence” of both MAP and diabetes, like the United States.  Johne’s disease is what you call the disease when livestock get infected by the bug.  The reason the diabetes researchers chose Sardinia, an island off the coast of Italy, is because “paratuberculosis is present in more than 50% of Sardinian herds.”

If they think that’s bad, though, the last national survey of dairy herds in the U.S. shows 68% are infected with MAP, especially those big industrial dairies; 95% percent of operations with more than 500 cows came up positive.  It’s estimated the disease costs the U.S. industry more than a billion dollars a year.

How do people become exposed?  “The most important routes of access of MAP into the human food chain appear to be contaminated milk, milk products, and meat from infected cattle, sheep, and goats.  MAP or MAP DNA has been detected in both raw milk and pasteurized milk, infant formula, cheese, ice cream, muscle and organ tissues, and retail meat.”

How do we know paraTB bacteria survive pasteurization?  Because Wisconsin researchers bought hundreds of pints of retail milk off store shelves from three of our top milk-producing states, and tested for the presence of viable (meaning living) MAP bacteria in retail milk and 2.8% came back positive for live paraTB bacteria, with most brands yielding at least one positive sample.  So, it can survive pasteurization.

If paraTB does end up being a diabetes trigger, then “these findings indicate that retail milk in the United States would need to be considered as a transmission vector.”  Why hasn’t the public heard about this research?  Perhaps, because the industry isn’t too keen on sharing.  This is from the Journal of Dairy Science: “Fear of consumer reaction can impede rational, open discussion of scientific studies.”

The galactose sugar in milk may explain why milk consumption was associated with significantly higher risk of hip fractures, cancer, and premature death.  Here is the research. 

Milk is touted to build strong bones, but a compilation of all the best studies found no association between milk consumption and hip fracture risk, so drinking milk as an adult may not help bones.  But what about in adolescence?  Harvard researchers decided to put it to the test.

Studies have shown that greater milk consumption during childhood and adolescence contributes to peak bone mass, and is therefore expected to help avoid osteoporosis and bone fractures in later life.  But that’s not what they found.  Milk consumption during teenage years was not associated with a lower risk of hip fracture and, if anything, milk consumption was associated with a borderline increase in fracture risk in men. 

It appears that the extra boost in total body bone mineral density you get from getting extra calcium is lost within a few years, even if you keep the calcium supplementation up.  This suggests a partial explanation for the long-standing enigma that hip fracture rates are highest in populations with the greatest milk consumption.  Maybe an explanation why they’re not lower, but why would they be higher?

This enigma irked a Swedish research team, puzzled because studies again and again had shown a tendency of a higher risk of fracture with a higher intake of milk.  Well, there is a rare birth defect called galactosemia, where babies are born without the enzymes needed to detoxify the galactose found in milk, so they end up with elevated levels of galactose in their blood, which can cause bone loss even as kids.  So, maybe, the Swedish researchers figured, even in normal people that can detoxify the stuff, it might not be good for the bones to be drinking it every day.  And galactose doesn’t just hurt the bones, that’s what scientists use to cause premature aging in lab animals.  They slip them a little galactose and you can shorten their lifespan, cause oxidative stress, inflammation, brain degeneration, just with like the equivalent of, you know, one to two glasses of milk’s worth of galactose a day.  We’re not rats, though—but given the high amount of galactose in milk, recommendations to increase milk intake for prevention of fractures could be a conceivable contradiction.  So, they decided to put it to the test, looking at milk intake and mortality, as well as fracture risk, to test their theory.

A hundred thousand men and women followed for up to 20 years; what did they find?  Milk-drinking women had higher rates of death, more heart disease, significantly more cancer for each glass of milk.  Three glasses a day was associated with nearly twice the risk of death and they had significantly more bone and hip fractures too.

Men in a separate study also had a higher rate of death with higher milk consumption, but at least they didn’t have higher fracture rates.  So, a dose-dependent higher rate of both mortality and fracture in women, and a higher rate of mortality in men with milk intake, but the opposite for other dairy products like soured milk and yogurt, which would go along with the galactose theory, since bacteria can ferment away some of the lactose.  To prove it though, we need a randomized controlled trial to examine the effect of milk intake on mortality and fractures.  As the accompanying editorial pointed out, we’d better figure this out soon, as milk consumption is on the rise around the world. 

Does the hormonal stimulation of human prostate cancer cells by cow’s milk in a Petri dish translate out clinically in studies of human populations?  Let’s, look at the facts. 

“Concern has been expressed about the fact that cows’ milk contains estrogens and could stimulate the growth of hormone-sensitive tumors”—concern that the “consumption of dairy products could both promote the conversion of precancerous lesions or mutated cells to invasive cancer and enhance the progression of hormone-dependent tumors.”

This was initially postulated based on suggestive population-scale data:  25-fold increase in prostate cancer in Japan since the war.  What was happening to their diets during that period?  A 5-, 10-, 20-fold increase in eggs, meat, and dairy consumption, whereas the rest of their diet remained pretty stable.  But, diet wasn’t the only major change in Japanese lifestyles over the latter half century.  Similarly, even though countries with higher milk consumption tend to have more prostate cancer deaths, and countries with lower milk consumption fewer deaths, there could be hundreds of confounding variables.  But, it certainly does spur interest in studying the possibility.

Controlling for as many factors as possible by just isolating prostate cancer cells out of the body in a Petri dish, and dripping cows’ milk on them directly.  They chose organic cows’ milk because they wanted to exclude the effect of added hormones, and just test the effect of all the growth and sex hormones found naturally in all milk. 

They found that “cows’ milk stimulated the growth of human prostate cancer cells in each of 14 separate experiments, producing an average increase in cancer growth rate of over 30%.  In contrast, almond milk suppressed the growth of these cancer cells by over 30%.”

But, just because something happens in a Petri dish, or a test tube, doesn’t mean the same thing happens in a person.  It’s just suggestive evidence that can be used in a grant application or something to get money to study actual people.  There’s kind of two main ways that’s done—retrospective studies looking back, where you take prostate cancer patients, and figure out what they ate in the past, and prospective studies looking forward, where you look at people’s diets first, and then follow them for a few years, and see who gets cancer.  The looking-back kind are called case-control studies, where they look at cases of cancer, and compare their diets to controls.  And the forward-looking kind are called cohort studies, because you’re following a cohort of people forward.  Then, if you want to get fancy, you can do a so-called meta-analysis, where you combine all the best studies done to date into one, and see what the balance of available evidence shows.  Okay, so, here we go:

The latest meta-analysis of all the best case control studies ever done on the matter concludes that milk consumption is a risk factor for prostate cancer.  And the latest meta-analysis of all the best cohort studies ever done also concludes that milk consumption is a risk factor for prostate cancer.  An even newer study suggests that milk intake during adolescence may be particularly risky in terms of potentially setting one up for cancer later in life. 

Despite hormone-related cancers being among our top killers, as pointed out in the Journal of the National Cancer Institute, “We simply do not know which hormones, and how much, are in the food we ingest.  More effort has been directed at the investigation of illicit use of designer steroids by Olympians and ballplayers than to the investigation of the effect of dietary hormones on cancer, and other diseases that affect millions.”  A proposal is therefore made “to monitor levels of steroid and other hormones and growth factors in all dairy and meat-containing foods”—though, to date, this has not been done.

To see any graphs charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need plus links to all the sources we cite for each of these topics.

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Thanks for listening to Nutrition Facts.  I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.