I’ve been reserving judgment on dairy products for 55 years now–since Grade 1, when my mom lied to the school authorities and told them I was allergic to milk. Truth was: it made me gag.
But now that Dr. Walter Willett, chairman of the Department of Nutrition, Harvard’s School of Public Health, and an esteemed panel of scientists have opined on the subject and we’ve had time to reflect, I can say this with certainty about whether or not dairy products have any place in an anti-cancer diet:
The US and Canadian guidelines suggesting at least 3 servings a day of dairy products, especially low or fat-free ones, are clearly wrong. At that level, dairy products may be driving cancers of the reproductive organs, no matter what the fat content. And this is the number 1 puzzle that nutritional scientists need to solve–now!
Yes, some dairy products (milk, not cheese) may protect against colorectal cancer, says the World Cancer Research Foundation and American Institute of Cancer Research (WCRF/AICR), whose international team of scientists have been evaluating the studies on diet and cancer since the 1990s. But what’s the point in eating foods that may promote cancer in other organs?
Dairy and Prostate Cancer
For men, the studies in human populations are quite clear. High calcium–more than 1500 mg a day– is probably associated with prostate cancer, says WCRF/AICR. (Some studies have also found an association with testicular cancer.)
“(T)he evidence that milk consumption is related to prostate cancer risk is actually very strong, specifically for aggressive and fatal prostate cancers,” Willett said in 2006 during a symposium at McGill University.
Have scientists learned anything since that time that would change his view? “(W)e don’t have any substantial new data on this topic,” he said.
Dairy and Female Cancers
For women, while the studies in breast cancer are mixed, what’s particularly troublesome are studies linking dairy to ovarian cancer, specifically three large studies showing an association with even small amounts.
● In Sweden, where dairy product consumption and ovarian cancer rates are high, researchers followed more than 60,000 women over an average 13 1/2 years—and found that compared to women who never or seldom drank milk, women who consumed more than 1 glass of milk a day had double the risk of a very common and aggressive type of ovarian cancer typically not found until late stage.
Those results were consistent with two earlier studies.
● Harvard’s Nurses’ Health Study, an ongoing look at various issues in women’s health that Willett has been spearheading, found that women who consumed one glass or more a day of skim or low fat milk had a 69 percent increase in that same deadly ovarian cancer compared to women who almost never drank milk. And compared to women who almost never ate yogurt, women who consumed five or more servings a week were more than twice as likely to develop that cancer.
●And the Iowa Women’s Health Study of postmenopausal women found that those who drank more than 1 glass of skim milk a day had a 73 % greater risk of ovarian cancer than those who drank less or none of it.
While “the evidence is not as firm or as robust as it is for prostate cancer risk,” Willett said at that symposium, “it has to make one worried about recommending three servings of milk a day,” especially since ovarian cancer is so deadly.
Is it the calcium?
Scientists aren’t totally sure what mechanisms are at play.
High calcium intake can disturb your production of Vitamin D, the sunshine vitamin, which, in animal and cell studies, keeps cancer cells from proliferating and helps them revert to their non-cancerous states. The current US recommendations for dietary calcium may be too high, Willett suggested.
But calcium might not be the–or the only–culprit.
The Swedish and Harvard studies in women both found an association with lactose, or milk sugar. For each 10–11 grams of lactose a day (equivalent to a glass of milk), there was a 20 percent greater risk. One component of that sugar, molecules of galactose, may be particularly harmful to ovaries.
Or is it the proteins sending signals?
A German dermatologist who has found that dairy products are linked to both acne and prostate cancer says that the problem is milk’s amino acids. Milk proteins trigger a cascade of signals that tell all cells to grow.
“Sustained proliferation is the most critical hallmark of cancer. That is what milk is doing, a program of mammalian evolution intended to be operative only in the postnatal nursing period and not for life-long abuse!” said Dr. Bodo Melnik.
Ever wonder why body builders flock to whey protein supplements after workouts?
Dairy products contain two types of protein: casein, abundant in the amino acid methionine, and whey, rich in the amino acid leucine.
Leucine triggers muscle growth. It helps build muscle by directly activating a compound in muscle called the mammalian target of rapamycin (mTOR). In conjunction with other compounds, mTOR functions as a molecular switch, a hub for coordinating the complex signaling system involved in sending messages within cells. Leucine flips the switch, turning on the machinery that tells your cells to manufacture muscle proteins.
The problem is: Cancer cells also take advantage of this continually open switch—constant mTOR signalling—in order to keep proliferating.
Casein, according to T. Colin Campbell’s decades of research (“The China Study”), has demonstrated a “remarkable ability to promote cancer growth in test animals when consumed in excess of protein needs,” and in animal and cell studies, dietary restriction of methionine inhibits and reverses tumor growth.
Both proteins, Melnik says, stimulate the production of hormones that indirectly activate more mTOR signaling–insulin and Insulin Growth Factor-1 (IGF-1). These hormones also send messages that signal cells, including cancerous ones, to grow and that lead to reductions in your Sex Hormone Binding Globulin, leaving estrogen and testosterone to circulate in your blood.
High levels of IGF-1 have been associated with many cancers, including prostate and estrogen positive breast cancer. Cancers driven by androgens may be particularly susceptible to dairy, suggests Melnik. (Yes, androgens are traditionally considered male hormones but they’ve been implicated in breast and ovarian cancer; the enzyme aromatase turns androgens into estrogens.) IGF-1 stimulates a very potent form of testosterone that activates mTOR signaling, and in what scientists call “cross-talk,” overactive mTOR signaling may then drive production of even more testosterone, he explains.
The female hormones in milk from pregnant cows may also play a part, he says.
He’s particularly concerned about dairy products during puberty. During this sensitive time period, the pituitary gland is already secreting large amounts of growth hormone, which stimulates the liver to produce IGF-1. In one study, daily milk consumption during adolescence more than tripled the risk of aggressive prostate cancer later in life.
(Leucine also stimulates the oil-producing glands, and dairy products during puberty have also been linked to teenage acne. Another study found an association between severe long-lasting acne and increased risk of prostate cancer later in life. )
To read more about Melnik’s work on dairy and prostate cancer, see this review and this one . For his diet and acne work, see this article and this one. For a discussion of insulin and IGF-1, see this.
What about your bones?
Don’t we need milk for strong bones?
That’s a myth, Willett said. “Every large study that has looked at this issue has found that there is no reduction in fracture risk with higher dairy consumption, very consistent findings, all the way up to over 4 glasses of milk a day,” he told the symposium. He’s just published a study showing that milk consumption in adolescence may actually increase fracture risk.
Are all dairy products created equal?
The US government has been urging consumers to switch from full to low or non fat dairy, but if the calcium or sugars/lactose or proteins/amino acids are driving cancer, then low fat products are not any better—and perhaps even worse.
The fat content of milk doesn’t alter its lactose content. In fact, two percent, low and nonfat cow’s milk actually have more leucine and more calcium than whole. And sheep’s milk has around twice as much leucine as bovine secretions.
So what’s the dairy product that’s lowest in proteins? Butter. It’s virtually all fat.(But high intakes of saturated animal fats may be associated with some cancers, so treat it like Brylcreem–a little dab ‘ll do ya.)
How much is too much?
That’s hard to say, Willett told the symposium. With adults, “ probably one serving a day is the level where we don’t really see much evidence of harm,” he said. “(W)e start to get concerned about two or three servings a day because it looks like there is some strong potential for harm, particularly for men and maybe for women. For children, of course, everything is much more complicated, and we also have much less data.”.
Talk about complicated!
The few studies on dairy consumption after cancer diagnosis suggest that it may depend on your diagnosis–for women with breast cancer, whole but maybe not low fat products may drive progression; for men with prostate cancer, avoiding all dairy may be the most prudent:
- breast cancer: High but not low fat dairy related to higher risk of dying.
- breast cancer: Lower intake of saturated and trans fats linked to survival.
- prostate cancer: Dairy, both high and low fat, linked to higher risk of dying.
The bottom line, for us adults, for now
Thank goodness for plant milks!
When it comes to IGF-1, of all foods dairy products appear to be the largest contributor —more so than animal muscle. In contrast, the hormone is substantially lower in people on plant-based diets. Plants contain large amounts of IGF-1 binding proteins, and according to Melnik, many have components that can naturally inhibit mTOR signaling–
- green tea
- whole soy
- resveratrol and–get this–
(Metformin, a drug commonly used to control insulin levels in type 2 diabetics, also lowers mTOR signaling, he says, but I’ll save that success story for another day.)
It looks like my gut was right in rejecting cow’s milk way back when. Until the science becomes more certain, I’ll be practicing the precautionary principle of anti-cancer diets and sipping an almond milk latte in the sunshine. Thanks, mom. I won’t tell anyone else about your little milky lie.
© 2014 Harriet Sugar Miller