OVERVIEW
· What’s happened to the reputation of milk, the staple drink of our childhood?
· Why do so many people shy away from dairy products, believing them to be the cause of two of our most common cancers, prostate and breast? We uncover the evidence, which paints a rather different picture of milk.
· Rather than cancer causer, could milk be a cancer protector?
‘Milk has gotta… lotta bottle, milk has gotta… lotta bottle, milk has gotta… lotta bottle, nice cold, ice cold milk!’ went the slogan of the UK Milk Marketing Board’s 1980s TV commercial, which put milk back on the map. Promoted as a health food, milk was suddenly cool to drink. ‘It’s got minerals and vitamins, to keep a body fit’ we were told, and if the ads were to be believed, it was the favourite drink of sky divers, astronauts, racing drivers, and, for reasons unknown to us, women who enjoyed writhing around in shiny catsuits. But it seems the tide has turned in recent years, with our penchant for milk and dairy products undermined by the popular ‘health’ press. The anti-milk brigade tell us that milk is the cause of a whole host of diseases, with breast cancer and prostate cancer topping the list.
We weren’t so sure it all stacked up, so we went on a mission to take a closer look.
‘The China Study’
Let’s kick off with a classic example, The China Study. This highly influential and bestselling book indicts animal-based foods as being the root cause of our so-called Western diseases. Its message is clear: avoid all animal-based products or face the consequences. The most persuasive (or should that be terrifying?) argument for avoiding animal-based foods is their purported effect of increasing the risk of developing cancer. To cut a long story short: if cancer were a fire, animal products would be the matches, the kindle and the fuel.
Well, that got our ears pricked up and we imagine yours too. There are no prizes for knowing that our modern-day diets lack plant foods: fruit, vegetables, wholegrains, legumes, nuts, and so on. Nor for thinking that if we dropped some of the meat products we consume with such gusto in favour of more plant foods, we would reap the benefits from ingesting more beneficial phytochemicals. We’ve no bones to pick with any of that.
But this wasn’t the message being promoted. It was that animal products themselves, especially dairy products, were in the dock and charged with causing cancer. Yet, since 2004, when The China Studywas published, there’s been a raft of scientific research on this subject. So we took it upon ourselves to examine the three main cancers discussed in The China Study – prostate, breast and colorectal – to see if the evidence really stacked up. Next time we opened the fridge and laid eyes on the milk, cheese and yoghurt, would we recoil from it in the knowledge that we were staring at the source of our demise?
The dairy industry is massive in the USA, and valued in excess of a colossal $35 billion for the dairy farmers. In California, one fifth of the entire state’s gross income is from milk production. The top dairy processors (Dean Foods, Kraft Foods, Land O’Lakes, Schreiber Foods, The Kroger Co. and Dairy Farmers of America) alone boasted sales of $26.5 billion in 2005.
You do the maths
Dairy products have been singled out as a primary culprit in the inexorable rise of prostate and breast cancer in the modern world, and it seems as if pretty much every ‘alternative’ health practitioner has got it in for the white stuff. This is fuelled by the massive variation seen in the rates of these diseases across different countries. For prostate cancer, the incidence is about 80 times greater in the USA than in China1. It’s not quite as extreme for breast cancer, but still somewhere in the region of four times higher in the USA compared with Asian countries2. The anti-dairy contingent put these differences down to the fact that dairy products are consumed in large amounts in the West, but are practically non-existent in traditional Asian diets. To put it bluntly, we may as well be ingesting poison.
If you take a look at some of the science, it’s not all that difficult to find studies to back up the anti-dairy soothsayers. Let’s take prostate cancer, which shows the most extreme variation between West and East. In a study of 42 countries, milk consumption was closely correlated to prostate cancer occurrence3. That basically means the countries that guzzle the most milk get the highest rates of prostate cancer. Likewise, when we look at evidence from a number of case control studies, the risk of prostate cancer was cited to be 70% higher in those who consume milk4.
So, if you just looked at these associations and nothing else, you’d be right to suspect dairy as the most heinous of foods. And you’d have little trouble constructing an almost identical argument when it comes to breast cancer, too. The stats look even more incriminatory when you look at what happens when people migrate from an area of low risk to an area of high risk (say, moving from Asia to the USA). The risk shoots up and within just one or two generations, Asians adopt the high risk of their host country. This tells us that it’s the environment, not genetics, that’s driving the stats up.
However, it’s simply bad science to compare and contrast countries in this way. Do we actually think that we can take two totally different cultures and pin the differences in disease onto one single isolated dietary factor? Sure, it does have some intuitive appeal. China’s dairy consumption is more than seven times less than that of the USA5. And even these low intakes for China still represent almost a doubling of dairy consumption in the last decade, with the greatest increases seen in the rapidly expanding urban population (urban intakes are five times that of rural intakes)5. And the idea is bolstered when we see that at the same time as this increased dairy intake, there was a 20–30% increase in reported rates of breast and prostate cancer6. But does it really all add up?
The thing is, we’re talking about very different ways of life here, and far more differs than just dairy intake (better screening programmes, earlier detection, starting menstruation at a younger age, delaying having children, obesity rates and use of hormonal medications are just some of the things that might differ in the USA compared with China). But, while it seems ridiculous to blame the whole disparity on dairy products, it is still very possible that they have some role to play. So let’s shed some real light on this and see what the studies have to say.
Dairy consumption started about 7,500 years ago in Central Europe and, as a result, Europeans have evolved to maintain the lactase enzyme, which digests milk sugar, throughout life. In contrast, many ‘nouveau’ dairy cultures, such as Asians and Africans, haven’t made this adaptation and are generally lactose intolerant in adulthood.
Genetic factors may account for up to 10% of breast cancer cases in the developed world – a figurer far too low to explain the large variation in risk seen across different countries1.
Prostate cancer
It’s time to broaden our net and see what else is out there. In 2007, a major review of the evidence on diet and cancer was reported by the World Cancer Research Fund7. Comprehensive in scope, this would proffer some seriously authoritative facts and figures when it came to assessing the risk of dairy products in relation to prostate cancer. The report found an average increased risk of 6% per serving of dairy products (a serving being about 250ml milk) per day, so while apparently modest, the finding was surely enough to strike concern into the hearts of the dairy-gorgers.
The reason for this, it was suggested, is the high calcium content of milk. In support of this, a meta-analysis found that the highest calcium consumers had a 39% increased risk of prostate cancer compared with the lowest calcium consumers8. Results of the EPIC study published in 2008 proffered further support for this finding. While it found that just yoghurt intake, not milk or cheese, was associated with prostate cancer, when you added up all the calcium derived from dairy foods, those with the highest intakes had an increased risk of prostate cancer of 18% compared with those who had the lowest intakes9.
So, it seems it’s not milk per se that increases the risk of prostate cancer, but the fact that it’s laden with large amounts of calcium. The evidence appears to point to a threshold for calcium intake. Hit about 1,500mg or more per day and the risk of prostate cancer starts to really take off7,10.
And is that really so surprising? Time and time again, the nutritional literature shows us that an over-reliance on very large amounts of a single nutrient can end up being harmful. As for calcium, there’s never any need to ingest 1.5g or more a day, regardless of the source. Indeed, the increased risk isn’t likely to be caused by high amounts of calcium itself, but the imbalance these mega amounts create within the body. What we need to do is keep our calcium intake in balance with our vitamin D levels, and taking masses of calcium can start to unravel that delicate equilibrium. Considering we are already a vitamin D-deficient population, the high calcium intake simply puts the balance further out of whack, which is not good news when it comes to prostate cancer risk.
It’s estimated that 43% of the US population (and a majority aged over 70) takes a supplement containing calcium11.
While a typical adult male in the USA consumes about 1,250mg of calcium a day11, in China the estimated intake is a meagre 388mg and dairy contributes only 4.3% to the average daily calcium intake5. In China, the primary sources of calcium are vegetables, beans and bean products, wheat and rice5.
Men concerned about prostate cancer should avoid consuming more than 1.5g calcium per day. That amount of calcium would be found in just over 1 litre of milk (or equivalent servings of other dairy foods). But remember that calcium is also found in other foods, and in some supplements, too.
THE SCIENCE BLAST: CALCIUM, VITAMIN D AND PROSTATE CANCER
There’s an interesting subplot to all of this. Those consuming the greatest amount of dairy products, associated with an increased risk of prostate cancer, tend to live at higher latitudes. With less sunshine, that also means they are a population with the lowest vitamin D levels. This lack of vitamin D results in reduced formation of the active form of the vitamin (known as 1,25(OH)2D) by the kidneys. In this situation, ingesting large amounts of calcium sets off a signalling system that reduces the active 1,25(OH)2D even further, reducing the body’s defences against cancer and increasing cell proliferation in the prostate. This was borne out in a study that observed that calcium, which reduced active vitamin D formation, increased prostate cancer occurrence, whereas fructose, which increases active vitamin D formation, reduced prostate cancer risk13.
Intriguingly, a US study published in 2005 found an association with increased prostate cancer risk only with low-fat milk consumption and not full-fat milk14. We should also point out that milk in the USA is often fortified with vitamin D, which is fat-soluble. That means the low-fat version will have more calcium, but less vitamin D availability; more evidence for the importance of vitamin D in this whole debate.
So, it looks like it could be the low vitamin D levels, rather than the milk or calcium, that are the real problem. If you’re already deficient in vitamin D (which, as we know, is all-too common) a high intake of calcium will just exacerbate the problem. It all boils down to getting enough vitamin D.
To illustrate the point, we’ll look at a study that gave a pretty high dose of calcium supplements (1,200mg per day) to men already consuming 900mg calcium a day from the diet15. Based on what we know so far, we might expect this to increase prostate cancer risk. But it didn’t. What you need to know about the subjects in this study is that they already had ideal vitamin D levels (at 30ng/ml). Vitamin D was in plentiful supply, which negated any harmful effects of a high calcium intake. So while the researchers found that the subjects given the calcium supplements had lower levels of the active form of vitamin D, made by the kidneys, the prostate would still have been able to make its own active vitamin D because the body stores were ample. If they’d started off with much lower vitamin D stores, it would probably have been a different story altogether.
Nutrients work together. Taking calcium as an isolated supplement is linked with around a 30% increase in heart attacks12.
Hidden hormones
Time and time again, we hear that milk is bad for us because of the hormones it contains. Specifically, it is insulin-like growth factor (or IGF-1 for short) that’s taken the rap for increasing cancer risk. IGF-1 causes cancer cells to grow, and raised levels are associated with a 47% increase in prostate cancer in men16 and a 233% increase in breast cancer in premenopausal women17. With milk raising IGF-1 levels by about 10%18, it’s no wonder that dairy products are eyed with such suspicion by some.
But the evidence just doesn’t stack up. Studies support the idea that soy can help reduce the risk of prostate cancer19, and evidence suggests that consumption of soy throughout life may offer some protection against breast cancer20. Indeed, it is invariably the anti-dairy contingent who vociferously urge that we dump the dairy in favour of soy-based products. Yet ironically, soy protein actually increases IGF-1 levels significantly more than dairy does, with the magnitude of difference more than twofold21.
In reality, IGF-1, made in the body from Growth Hormone, is essential for health and is dubbed an anti-ageing hormone. The problem is that IGF-1 doesn’t discern between healthy cells and cancer cells, so if cancer is present it will promote its development. Once again, this underlines why prevention is better than cure. The job of preventing cancer formation in the first place is down to factors such as eating an optimal diet, getting enough phytonutrients, selenium and vitamin D, staying physically fit and maintaining a healthy weight.
Breast cancer
Of all the popularized diets for combating breast cancer, going dairy-free is easily the most widely propagated. As is the case with prostate cancer, the soothsayers cast dairy products as some sort of demonic perpetrator in causing breast cancer. If you want to stay free of breast cancer, you’re told to ditch the witch.
Again, we turn to results from the EPIC study to shed some much-needed light on this. Studying the dietary habits of well over a quarter of a million women, the results found no consistent link between dairy products and breast cancer risk22. Then we have some fascinating results from a meta-analysis of 18 prospective cohort studies published in 2011, which found that overall, dairy products reduced breast cancer risk by 15% in those consuming the highest amounts, compared to those consuming the lowest23. This effect appeared stronger for low-fat rather than high-fat dairy products.
What’s pretty clear is that dairy products, especially the low-fat varieties, have unnecessarily been given a bad rap. We simply don’t think the science justifies it. It gets even more intriguing when we look specifically at calcium, which is found abundantly in dairy products. Lab studies have shown that calcium has anti-proliferative and pro-differentiation effects on mammary cells (so basically, anti-cancer effects), and in rats it inhibited the development of breast tumours24.
Obviously we need data from human studies too, and when 15 studies on calcium intake and breast cancer were pooled together, there was a 19% decrease in breast cancer occurrence in those with the highest levels of calcium intake compared to those with the lowest25. There we have it. One of the key nutrients found in dairy products actually seems to protect against breast cancer.
When we also consider the strong association of vitamin D with breast cancer, it reinforces the importance of ensuring that calcium intakes are balanced with sufficient vitamin D levels25.
Milk – an anti-cancer food?
Which brings us nicely to our final point. Why is it we only ever hear about the bad stuff? You could be forgiven for envisaging dairy as a digestive death sentence, so vociferously is it denounced. The dairy-bashing crusade is unrelenting, and its disciples are unwilling to give dairy any kudos. Well, for once, we’re going to give you the positive spin. When it comes to breast cancer, instead of causing harm, we’ve seen that low-fat dairy, if anything, appears to exert a beneficial effect. The case for colorectal cancer is stronger still, with little doubt that it does a power of good. Studies consistently show evidence of protection from dairy intake. A meta-analysis of 19 cohort trials, published in 2012, found a 17% reduction in colorectal cancer from a 400g per day intake of dairy products26. The association was strongest for milk, with a 200g serving per day reducing the risk by 9%.
When we add in evidence from RCTs, the case gets even stronger. These show that the calcium in low-fat dairy reduces colon cancer risk by decreasing epithelial cell proliferation and improving cellular differentiation27,28. Calcium can also bind fats and bile, preventing their irritating actions on gut cells.
THE PARTING SHOT
When it comes to cancer, it’s pretty apparent that dairy has earned an undeservedly negative reputation. It seems that mother knew best when she said, ‘milk does a body good’. So, next time the fear-mongers inform you that you’re downing gasoline for the cancer fire, just turn and give them that white-moustached smile. Not only does the evidence fail to stand up, but dairy products, especially the low-fat variety, can actually reduce our cancer risk. As with everything, there is no need for extremes. If intakes are balanced, we can only conclude that dairy should reclaim its place as part of a healthy diet.
Got milk? Yes, please…
SUMMARY AND RECOMMENDATIONS
· There shouldn’t be a blanket ban on dairy products for fear of increasing cancer risk.
· For men concerned about prostate cancer, it would be wise not to exceed 1,500mg of calcium per day (remembering that calcium is found in a diverse range of foods, not just dairy products).
· Maintaining an optimal level of vitamin D (20–32ng/ml), as described in Chapter 7, will further reduce any adverse consequences of dairy products on prostate cancer risk.
· There is no evidence that dairy products have an adverse effect on breast cancer risk; if anything, low-fat dairy products look likely to be protective.
· The most promising finding is that dairy products, especially milk, protect against colon cancer.